Chapter 3. Radiology

Diagnostic imaging is an essential component of the evaluation of many otolaryngologic problems. Computed tomography (CT) and magnetic resonance imaging (MRI) are the most commonly used imaging modalities, with positron emission tomography (PET) playing an ever-increasing role.

Computed Tomography

CT scanning uses ionizing radiation to generate cross-sectional images based on differences in the X-ray attenuation of various tissues. Modern scanners are typically helical, meaning that X-ray source rotation and patient translation occur simultaneously; this results in the acquisition of a “volume” of data that is then partitioned and reconstructed into individual slices. Helical scanning is significantly faster than traditional slice-by-slice acquisition, thereby diminishing artifacts related to motion (eg, breathing, swallowing, and gross patient motion). The rapid data acquisition also allows a larger number of thinner slices to be obtained, which facilitates diagnosis by decreasing partial-volume averaging effects and allows for improved quality of multiplanar reconstructions. The most recent advance in CT imaging has been the introduction of “multislice” scanners. Multislice scanners have a variable number (typically 8–64, though scanners with 320 are now available) of parallel arcs of detectors that are capable of simultaneously acquiring volumes of data. The increased speed that results from multislice sampling can be traded for improved longitudinal resolution, an increased volume of coverage, or an improved signal-to-noise ratio.

CT scanning of the head and neck is ideally performed with thin sections, usually ≤3 mm, in the axial plane; with multislice scanners, 0.625- or 1.25-mm slices are typically acquired and then combined for ease of viewing into slightly thicker 2.5- to 3-mm slices. Direct coronal imaging or coronal reformations are useful in many situations, notably in imaging of the paranasal sinuses and the skull base, and sagittal reformations can also be useful. Because of growing concerns over medical radiation, coronal reformations are generally preferred to a second acquisition if axial images are also acquired. CT scanning of the neck is generally performed following injection of iodinated contrast material because opacification of vessels helps to separate them from other structures such as lymph nodes and also helps to delineate and characterize pathology. If bony anatomy is the focus of the imaging study, as in imaging of the paranasal sinuses or temporal bones, then intravenous contrast material is not required. If a patient has a contrast allergy or renal insufficiency, then contrast administration should be avoided; premedication with steroids and antihistamines can be useful if a patient has a history of a contrast reaction, but contrast administration is necessary.

Magnetic Resonance Imaging

MRI exploits differences in relaxation characteristics and spin density of protons in different tissue environments to produce an image that is exquisitely sensitive to soft tissue contrast. Depending on the parameters that are selected, variable tissue characteristics and contrast are produced. At least two different types of sequences in two planes are generally necessary to characterize lesions of the head and neck. The slice thickness should be no more than 5 mm. A gadolinium-based contrast agent is generally used to enhance the detection of pathology and improve tissue characterization, and also to aid in the generation of a differential diagnosis. In some circumstances, thinner sections covering a smaller anatomic area may be necessary for more precise diagnosis.

In the head and neck, the following imaging sequences are typically obtained: (1) sagittal, axial, and coronal T1-weighted images; (2) axial fast spin-echo T2-weighted images with fat saturation; and (3) axial and coronal postgadolinium T1-weighted images with fat saturation.

Additional planes may be useful in some circumstances, such as coronal fast spin-echo T2-weighted images with fat saturation for the assessment of paranasal sinus and anterior skull base pathology. Additional sequences such as magnetic resonance angiography (MRA) may be useful in certain circumstances (eg, paragangliomas and dural fistulas), but are not necessary for evaluating most processes of the head and neck. MR venography may be useful in the assessment of patients with pulsatile tinnitus and in the assessment of the patency of the sigmoid sinus in patients with adjacent neoplastic or inflammatory disorders. Sequences such as FIESTA (fast imaging employing steady-state acquisition) or CISS (constructive interference in the steady state) allow heavily T2-weighted, thin-section imaging that is particularly useful in assessing the basal cisterns and fluid-filled inner ear structures and will generally be included in temporal bone-imaging protocols. Advanced modalities in widespread use in the brain (eg, MR spectroscopy, diffusion-weighted imaging, functional MRI) have for the most part not found a place in routine head and neck imaging, with the exception of diffusion-weighted imaging, which is particularly useful in the evaluation of the skull base and temporal bone for epidermoid cysts and cholesteatomas.

On a T1-weighted image, fat is bright and fluid (eg, cerebrospinal fluid [CSF]) is relatively dark. Muscle and most pathologies are of intermediate signal intensity. The large amount of fat in the head and neck provides intrinsic tissue contrast, which makes the T1-weighted image very sensitive to infiltrative processes that obliterate tissue planes or that replace marrow fat (Figure 3–1). Some hemorrhagic or proteinaceous lesions cause shortening of T1 relaxation time and appear bright on a T1-weighted image. On a T2-weighted image, fluid is very bright and most pathologies are relatively bright, whereas normal muscle is quite dark. The fast spin-echo technique is very useful in limiting artifacts related to motion and magnetic susceptibility compared with conventional spin-echo T2-weighted imaging. Because fat remains bright on a fast spin-echo image, however, fat saturation should ideally be applied when imaging the head and neck or skull base. In the nasal cavity and paranasal sinuses, T2-weighted images are particularly useful in distinguishing neoplastic masses from polyps, thickened mucosa, and retained secretions (Figure 3–2). Gadolinium is very useful for demonstrating pathology and tailoring a differential diagnosis based on the enhancement characteristics of a lesion. In a patient with head and neck cancer, postgadolinium imaging is also very useful in assessing cavernous sinus invasion, meningeal infiltration, and perineural spread of tumor (Figure 3–3). Fat saturation should ideally be applied on a postgadolinium T1-weighted image; otherwise, the contrast between an enhancing lesion and the high signal intensity of surrounding fat may actually be reduced compared with the pregadolinium image. Because low-field scanners often do not have fat saturation capability, high-field imaging (1.5 T or higher) is generally preferred for assessing the head and neck and skull base. If a patient is severely claustrophobic, then sedation may be necessary to accomplish the scan on a high-field system.

It should be kept in mind that MRI requires more time and more patient cooperation than does CT, and therefore, it is not necessarily suitable for acutely ill or uncooperative patients. In addition, there are certain absolute contraindications to MRI, including ferromagnetic intracranial aneurysm clips, cardiac pacemakers, and many cochlear implants. Therefore, patients must be carefully screened for these and other contraindications before undergoing MRI. Also note that gadolinium administration should be avoided whenever possible in patients with renal insufficiency due to concerns regarding nephrogenic systemic fibrosis (NSF), a progressive syndrome that involves fibrosis of skin, joints, eyes, and internal organs and that has been associated with exposure to gadolinium in the setting of renal dysfunction.

Positron Emission Tomography

PET provides a functional view of tissues rather than simply depicting anatomy. In the head and neck, it is used primarily for oncologic diagnosis and evaluation and is performed with the radiopharmaceutical 18F-fluorodeoxy-glucose (FDG). FDG is taken up into tissues in proportion to the glycolytic rate, which is generally increased in neoplastic processes. Focal asymmetric uptake is suggestive of a tumor but is nonspecific, since FDG is also concentrated in areas of inflammation. FDG PET scanning is particularly helpful in the following situations: (1) the search for an unknown primary lesion in a patient presenting with metastatic neck disease (Figure 3–4A), (2) the assessment of residual or recurrent disease after primary therapy, and (3) the search for synchronous or metachronous primary lesions or distant metastases. FDG PET scanning can also be useful for staging the neck, but there may be a significant number of false-negative studies in patients with clinically N0 necks because small tumor deposits (<5 mm) are generally not detectable on an FDG PET scan. These small tumor deposits are found if a neck dissection is performed. FDG PET scanning may also be used to assess response to organ-preserving therapy: if a short-interval PET scan demonstrates a marked decrease in metabolic activity, then the patient will continue to be treated with an organ-preserving regimen. If the metabolic activity of the tumor is not decreasing as expected, however, then the patient may be triaged to surgical resection at an earlier point in time. At present, most FDG PET scanning is done on dedicated PET-CT scanners; this allows fusion of the metabolic and anatomical information such that precise anatomic localization of regions of FDG uptake can be achieved (Figure 3–4B and 3–4C). PET-MRI scanners are currently being developed but are not yet available for clinical use outside of a few select research centers.

Spatial Anatomy of the Head & Neck

The spaces of the suprahyoid head and neck are defined by the three layers of the deep cervical fascia: the superficial, middle, and deep layers. The spaces so defined include the pharyngeal mucosal space (which includes the nasopharynx, oropharynx, and hypopharynx), the parapharyngeal space, the masticator space, the parotid space, the carotid space, the retropharyngeal space, and the perivertebral space. The infrahyoid neck has traditionally been clinically defined by a series of surgical triangles, but can also be described as a series of fascia-defined spaces, which facilitates the understanding and interpretation of cross-sectional imaging modalities such as CT and MRI.

The spaces of the infrahyoid neck are also defined by the three layers of the deep cervical fascia and include the superficial space (external to the superficial layer of the deep cervical fascia), the visceral space (including the thyroid gland, the larynx, and the esophagus), the carotid space, the retropharyngeal space, and the perivertebral space. The nasal cavity, paranasal sinuses, skull base, and temporal bone are considered unique subregions of the head.

Mucosal Disease of the Head & Neck

For mucosal disease of the head and neck, of which squamous cell carcinoma (SCC) is by far the dominant lesion, the traditional subdivisions are the nasopharynx, oropharynx, oral cavity, larynx, and hypopharynx. The pharyngeal mucosal space includes the nasopharynx, oropharynx, and hypopharynx.

Nasopharynx

Anatomy

The nasopharynx is bounded anteriorly by the posterior nasal cavity at the posterior choana; posterosuperiorly by the lower clivus, upper cervical spine, and prevertebral muscles; and inferiorly by a horizontal line drawn along the hard and soft palates (Figure 3–5). The lateral wall of the nasopharynx is composed of the torus tubarius, the eustachian tube orifice, and the lateral pharyngeal recess, also known as the fossa of Rosenmüller (Figure 3–6). In addition to squamous mucosa, the contents of the nasopharynx include lymphoid tissue (adenoids), minor salivary glands, the pharyngobasilar fascia, and the pharyngeal constrictor muscles. The pharyngobasilar fascia represents the aponeurosis of the superior constrictor muscle and attaches it to the skull base. A gap in the upper margin of the pharyngobasilar fascia is known as the sinus of Morgagni. The distal eustachian tube and levator palatini muscle normally pass through this gap, which also serves as a potential route of spread for nasopharyngeal carcinoma to access the skull base.

Pathology

Lesions that may be encountered on imaging studies of the nasopharynx are listed in Table 3–1. Adenoidal hypertrophy (Figure 3–7) is commonly seen in children, young adults, and patients who test positive for the human immunodeficiency virus (HIV), although in the latter group, lymphoma must be considered in the differential diagnosis. Nasopharyngeal carcinoma is the most common malignant lesion of the nasopharynx, and the spectrum of imaging findings that may be encountered with nasopharyngeal carcinoma is illustrated in Figure 3–8. Important issues to consider in the imaging assessment of a patient with nasopharyngeal carcinoma include the presence of extension to the parapharyngeal space and pterygopalatine fossa, the presence of skull base invasion, and the presence of extension to the cranial nerves or the cavernous sinus.

Key Imaging Points

• The lateral pharyngeal recesses may be asymmetric owing to mucosal coaptation rather than a true mass lesion. This “pseudomass” can be diagnosed when the clinician or radiologist identifies the “kissing” mucosal surfaces rather than a true mass lesion (Figure 3–9).
• The nasopharynx should be carefully scrutinized for a mass lesion obstructing the eustachian tube orifice in any adult patient with unilateral middle ear or mastoid fluid (Figure 3–10).
• Asymmetrically or unusually prominent nasopharyngeal soft tissue that is seen on an imaging study should prompt a clinical evaluation for neoplasm, especially lymphoma (particularly in the setting of HIV) or nasopharyngeal carcinoma (particularly if the patient is of southern Chinese descent) (Figure 3–11).
• Patients with nasopharyngeal carcinoma should undergo MRI rather than CT scanning for the most complete staging. In patients with nasopharyngeal carcinoma, the skull base should be carefully assessed on T1-weighted images for evidence of invasion, with particular attention to the clivus on a sagittal T1-weighted image. Postgadolinium, the cavernous sinuses and cranial nerves (notably V2 and V3) should be assessed for tumor involvement.
• Radiation necrosis of the temporal lobes may occur following high-dose radiation therapy for nasopharyngeal carcinoma, as may osteoradionecrosis of the skull base and cranial neuritis. These may mimic tumor recurrence on imaging studies (Figure 3–12).
• A patient with nasopharyngeal carcinoma may present with massive cervical lymphadenopathy yet a relatively small primary lesion. The nasopharynx should be carefully scrutinized in a patient presenting with noninfectious cervical lymphadenopathy, particularly when she or he is of southern Chinese descent.

Oropharynx

Anatomy

The oropharynx (Figure 3–13) is bounded anteriorly by the circumvallate papilla of the tongue, the soft palate, and the anterior tonsillar pillars, posteriorly by the superior and middle constrictor muscles, and superiorly by the soft palate. Inferiorly, it is separated from the larynx by the epiglottis and the glossoepiglottic fold and from the hypopharynx by the pharyngoepiglottic folds. In addition to squamous mucosa, contents of the oropharynx include the faucial and lingual tonsils, minor salivary glands, and pharyngeal constrictor muscles.

Pathology

Lesions that may be encountered on imaging studies of the oropharynx are listed in Table 3–2. Commonly encountered entities include tonsillar hypertrophy and tonsillar inflammatory processes, especially peritonsillar abscess. In a patient with inflammatory disease, it is important to look for underlying predisposing factors, such as an unsuspected foreign body, and also to look for potentially clinically occult complications, such as septic thrombophlebitis of the jugular vein (Figure 3–14). SCC of the faucial tonsil or base of tongue may present as a bulky exophytic mass lesion or an infiltrative mass lesion, or may have both infiltrative and exophytic components (Figure 3–15). In some cases the primary lesion may be very subtle (Figure 3–16). The margins of the lesion are often poorly defined, and there may be infiltration of adjacent normal fat planes. SCC is typically intermediate in signal intensity on both T1- and T2-weighted images and shows moderately intense enhancement postgadolinium. In a patient with known oropharyngeal SCC, the level II lymph nodes should be carefully scrutinized for evidence of metastatic involvement. Imaging of lymph nodes is discussed in more detail in a later section.

Key Imaging Points

• Lymphoid hyperplasia of the palatine or lingual tonsils, especially if asymmetric, may mimic an aggressive process such as SCC, but no invasive or infiltrative component will be identified (Figure 3–17).
• In a patient with a prior unilateral tonsillectomy, the remaining contralateral tonsil may appear to represent a mass lesion but is really a pseudomass (Figure 3–18).
• CT imaging is generally the modality of choice for the assessment of infectious and inflammatory processes because of its sensitivity to calcification, foreign bodies, and gas within soft tissues; it is also rapid and widely available. In the setting of peritonsillar abscess, CT scanning may show extension of the process beyond the confines of the pharyngeal constrictor muscles into adjacent deep spaces.
• Lingual thyroid tissue is seen as a rounded, midline soft tissue mass at the level of the foramen cecum. The lesion is intrinsically dense on a noncontrast CT scan because of its iodine content and enhances intensely postcontrast (Figure 3–19). In a patient with lingual thyroid tissue, the lower neck should be carefully scrutinized to assess whether any thyroid gland is present in the normal location.
• A well-circumscribed mass of the soft palate most commonly represents a pleomorphic adenoma, although a low-grade minor salivary gland malignant neoplasm may have an identical imaging appearance (Figure 3–20).
• The palatine tonsil and the base of tongue are common sites for “unknown” primary lesions in patients who present with metastatic cervical lymphadenopathy but with no obvious primary site lesion on careful head and neck examination. In some of these cases, CT scanning or MRI may demonstrate a primary site. FDG PET/CT scanning has also been shown to play a role in the search for the unknown primary.
• The possibility of perineural spread of tumor should be evaluated. Tonsillar SCC may invade the masticator space and access V3, whereas SCC of the base of tongue may access cranial nerves (CN) IX and XII (the glossopharyngeal and hypoglossal nerves, respectively), as well as the lingual nerve. Tumors of the palate may access the palatine nerves and the pterygopalatine fossa, from which they may spread intracranially via the vidian canal and foramen rotundum.

Oral Cavity

Anatomy

The oral cavity (Figure 3–21) is bounded superiorly by the hard palate, the superior alveolar ridge, and the maxillary teeth, laterally by the cheek, posteriorly by the circumvallate papilla and anterior tonsillar pillars (which separate it from the oropharynx), and inferiorly by the mylohyoid muscle, the inferior alveolar ridge, and the mandibular teeth. The mucosal area of the oral cavity includes the oral tongue and mucosa-covered surfaces, which are readily accessible to clinical examination. The oral mucosa has buccal, gingival, lingual, sublingual, and palatal surfaces. In addition to the ubiquitous squamous epithelium, minor salivary glands are located throughout the oral cavity.

Two other major spaces are also considered in any discussion of the oral cavity: the sublingual and submandibular spaces (Figure 3–22). These spaces are separated from each other by the mylohyoid muscle, which defines the muscular floor of mouth. The sublingual space is not a true fascia-defined space; rather, it is located in the oral tongue between the mylohyoid muscle inferolaterally and the genioglossus–geniohyoid complex medially. It freely communicates with the submandibular space around its posterior edge, and its important contents include the sublingual glands and ducts, the submandibular (Wharton) duct, the lingual artery and vein, the lingual nerve, and CN IX and XII. The submandibular space is located inferolateral to the mylohyoid muscle and superior to the hyoid bone. It is partly defined by the superficial layer of deep cervical fascia, but communicates freely with both the sublingual space around the back edge of the mylohyoid muscle and also the inferior parapharyngeal space. Important contents of the submandibular space include the submandibular gland, the level I lymph nodes, the facial artery and vein, and CN XII.

Pathology

The oral cavity is readily accessible to direct visualization and palpation, but imaging studies can be very helpful in assessing the deep extent of processes and guiding surgical management. In the mucosal area and oral tongue itself, the most common pathologies encountered are SCC (Figure 3–23) and extension of odontogenic infections. Benign or malignant minor salivary gland lesions may also be seen, as may congenital lesions such as venolymphatic malformations (Figure 3–24) and dermoids and epidermoids. In the setting of injury to or a lesion of CN XII, denervation change may be seen in the ipsilateral hemitongue, which may mimic a mass lesion to the unsuspecting observer.

Within the sublingual space, lesions that may be encountered on imaging studies are most frequently masses of congenital, inflammatory, or malignant neoplastic etiology. As in the mucosal space, venolymphatic malformations and dermoids and epidermoids may occur. A dilated submandibular duct due to stenosis, calculus, or neoplastic obstruction may be seen (Figure 3–25), as may a ranula (Figure 3–26). Changes due to cellulitis (Ludwig angina) and frank abscess formation may also be present. Finally, SCC extending from the mucosal surface of the oral cavity (Figure 3–27) or due to deep anterior extension from the tongue base may be encountered. A similar list of diagnostic considerations can be applied in the submandibular space, with a few important additions: notably, a second branchial cleft cyst (see Cystic Neck Masses later in this chapter) and lymphadenopathy, which may be reactive, inflammatory, or neoplastic, with nodal lymphoma and metastatic SCC accounting for most cases of neoplastic submandibular lymphadenopathy. Neoplastic lesions of the submandibular gland itself most commonly represent pleomorphic adenoma, but on imaging studies alone, these are often indistinguishable from carcinomas. The more common pathologies of the oral cavity and associated spaces are summarized in Table 3–3.

Key Imaging Points

• Because so much of the oral cavity is readily accessible to inspection and palpation, imaging studies must focus on addressing specific issues: submucosal and deep extension of neoplastic or inflammatory processes, bone involvement, and perineural spread of disease (Figure 3–28).
• Level I and II lymph nodes should be carefully assessed bilaterally in patients with oral cavity carcinoma, as bilateral nodal spread is common.
• The mucosal area of the oral cavity, particularly the buccal mucosa, can be better assessed on imaging examinations if the patient is asked to “puff out” his or her cheeks during a CT or MRI study to separate the buccal mucosa from the underlying teeth and gums (Figure 3–29).
• MRI is generally the study of choice to assess neoplasms of the oral cavity because it is less sensitive to dental artifact than CT scanning and provides superior soft tissue contrast for most processes (Figure 3–30).
• MRI is less sensitive to calcification than CT scanning; therefore, CT imaging is the study of choice for assessment of calculus disease, as well as for most infectious and inflammatory processes (Figure 3–31).
• In some cases, cellulitis and phlegmonous changes can be difficult to distinguish from an abscess. An abscess has a well-defined enhancing rim and a nonenhancing pus-filled center, and it exerts mass effect on local tissues rather than infiltrating along and obscuring fascial planes.
• A denervated hemitongue due to palsy of CN XII can mimic a mass lesion in the acute and subacute phases of denervation, when the tongue may be bright on a T2-weighted image and show enhancement postgadolinium (Figure 3–32). Denervation changes respect the midline perfectly, unlike most mass lesions. In addition, the lingual septum deviates toward rather than away from the “lesion,” and the tongue flops back into the oropharynx owing to atrophy and loss of muscle tone.
• A pedunculated mass of the parotid tail (Figure 3–33) may present clinically as a mass in the posterior submandibular space.

Hypopharynx

Anatomy

The hypopharynx represents the inferior continuation of the pharyngeal mucosal space, distinct from the oropharynx above and the larynx anteroinferiorly. Three major subsites of the hypopharynx are recognized: the pyriform sinus, the postcricoid area, and the posterior pharyngeal wall (Figure 3–34). The pyriform sinuses are bilaterally symmetric spaces marginated by the aryepiglottic folds anteromedially, the posterior thyroid cartilage ala laterally, and the most lateral aspect of the posterior hypopharyngeal wall posteriorly. The pyriform sinuses are shaped like inverted pyramids such that the tip of the sinus, also known as the pyriform apex, lies at the true vocal cord level. The postcricoid area forms the anterior wall of the lower pharynx at the level of the pharyngoesophageal junction, extending from the level of the arytenoid cartilages above to the inferior border of the cricoid cartilage below. This area is difficult to delineate on imaging studies because mucosal surfaces are usually coapted. The hypopharyngeal segment of the posterior pharyngeal wall extends from the bottom of the vallecula above to the esophageal inlet below. The hypopharynx contains only squamous mucosa, minor salivary glands, and the inferior constrictor muscles.

Pathology

The dominant pathology of the hypopharynx is SCC. Other lesions include retention cysts, benign and malignant tumors of minor salivary origin, and extranodal lymphoma. The pyriform sinus is the subsite most commonly involved with SCC, and these lesions are usually advanced at presentation and have a high incidence of nodal metastases (Figure 3–35).

Key Imaging Points

• The walls of the pyriform sinus are frequently coapted during imaging studies. Certain maneuvers, such as the Valsalva or “trumpet” maneuver, may help dilate the pyriform sinus and improve the imaging assessment.
• The pyriform sinus is a site where a small primary lesion may not be readily apparent in a patient who presents with metastatic cervical lymphadenopathy and no evidence of a primary lesion (“unknown primary”). It must therefore be carefully assessed on imaging studies performed in patients with metastatic cervical lymphadenopathy of unknown primary.
• A lesion of the pyriform apex approaches the upper margin of the cricoid cartilage and may erode cartilage even when relatively small. Cricoid erosion may also be secondary to a primary tumor of the postcricoid region (Figure 3–36).
• Symmetric lesions of the posterior pharyngeal wall may be subtle and difficult to detect on imaging studies. A sagittal T1-weighted image can be very helpful in these cases.
• Lesions of the hypopharynx have a propensity to spread to retropharyngeal nodes, so these nodes should be carefully scrutinized in patients with hypopharyngeal cancers (Figure 3–37).

Larynx

Anatomy

The soft tissues of the larynx (ie, the mucosa, the submucosa, and muscle) are draped over and attached to a supporting framework of cartilage, which gives the larynx its form. The endolarynx is divided into three subsites: the supraglottis, the glottis, and the subglottis (Figure 3–38). The supraglottis extends from the tip of the epiglottis above to the level of the laryngeal ventricles below and includes the epiglottis, the preepiglottic space, the aryepiglottic folds, the false vocal cords, the paraglottic space, and the arytenoid cartilages. The preepiglottic space is a fat-filled space bounded by the hyoid bone anteriorly and the epiglottis posteriorly, and halved by the hyoepiglottic ligament. The preepiglottic space communicates laterally with the paraglottic space, which is a bilateral, fat-filled space deep to the true and false vocal cords. The glottis includes the true vocal cords as well as the anterior and posterior commissures, whereas the subglottis extends from the undersurface of the true vocal cords above to the inferior surface of the cricoid cartilage below. The fibroelastic membrane known as the conus elasticus defines the lateral margin of the subglottis and extends from the cricoid cartilage below to the medial margin of the true vocal cord above.

The laryngeal cartilages include thyroid, cricoid, and arytenoid cartilages. The thyroid cartilage is composed of two anterior laminae that meet in the anterior midline. Posteriorly, the laminae elongate and form superior and inferior cornua; the superior cornua provide attachment to the thyrohyoid ligament, while the inferior cornua articulate medially with the cricoid cartilage and the cricothyroid joint. The cricoid cartilage is a complete ring that has a narrow arch anteriorly and a wide posterior lamina. The paired, pyramidal arytenoid cartilages sit atop the posterior cricoid lamina and provide attachment for the posterior margins of the vocal cords at the level of the vocal processes. The laryngeal cartilages progressively calcify and eventually ossify with age; in children and young adults they are of soft tissue density on CT scanning.

Pathology

Lesions that may be encountered on imaging studies of the larynx are listed in Table 3–4. SCC is the most common pathology of the larynx that requires an imaging assessment. Small lesions may not require imaging assessment and may in fact not even be visible on imaging studies, but CT scanning or MRI is useful in staging larger lesions. Involvement of preepiglottic and paraglottic spaces is well assessed on CT and MR scans, as is subglottic extension (Figure 3–39). Involvement of the laryngeal cartilages, notably the thyroid cartilage, may not be appreciated clinically but can be identified on imaging studies and has significant implications for therapy. MRI is more sensitive than CT scanning to neoplastic infiltration of the laryngeal cartilages, although neither technique is entirely reliable for detecting subtle invasion and both techniques may lead to overinterpretation of reactive changes as neoplastic infiltration. CT scanning or MRI is also useful in staging the neck, and both can detect pathologic lymphadenopathy that may be missed by clinical palpation.

Lesions primary to the laryngeal cartilages are classically chondroid in nature—for example, chondroma and chondrosarcoma. These lesions are centered on the cartilage, usually the cricoid cartilage, and appear as submucosal masses on direct inspection. A calcified matrix is typically present on CT scans, and these lesions are usually extremely bright on T2-weighted MRI. Ossified laryngeal cartilages may also be involved with systemic malignant processes such as lymphoma, leukemia, multiple myeloma, and hematogenously disseminated metastases from any primary site.

Trauma to the larynx is usually assessed clinically and endoscopically, but imaging may be useful when fracture of the laryngeal cartilages or deep tissue injury is suspected. Blunt trauma to the anterior neck compresses the larynx against the cervical spine. The thyroid cartilage most commonly fractures along its anterior margin (Figure 3–40), whereas the cricoid ring, like any complete ring, tends to fracture in two or more places.

The laryngocele results from functional obstruction (eg, increased intraglottic pressures) or true anatomic obstruction (eg, post-traumatic or postinflammatory stenosis, or neoplasm) of the laryngeal ventricle or its more distal saccule. The laryngocele may be filled with air, fluid, or pus and may be internal or external. The internal laryngocele is identified in the paraglottic space and can be followed to the level of the laryngeal ventricle. The external laryngocele has both an internal component, which may be completely collapsed, and an external component, which has penetrated the thyrohyoid membrane and often presents as an anterolateral neck mass (Figure 3–41).

Hoarseness is a relatively common indication for laryngeal imaging. In the absence of a mass lesion, attention should be focused on the course of the vagus nerve (CN X). When hoarseness is present along with other symptoms of lower cranial nerve dysfunction, then MRI is the study of choice to assess for a lesion of the skull base or carotid sheath (Figure 3–42). When hoarseness is the only symptom, then CT imaging is preferred, from the skull base to the aorticopulmonary window, to assess for any anatomic abnormality or mass lesion that could affect the recurrent laryngeal nerve along its course (Figure 3–43). The normal true vocal cords are symmetrically abducted during quiet respiration, whereas the Valsalva maneuver adducts the vocal cords to an opposed, midline position. In the setting of vocal cord paralysis, the paralyzed cord is usually fixed in a paramedian position, the ipsilateral aryepiglottic fold deviates medially, the ipsilateral pyriform sinus is dilated, and the laryngeal ventricle is often patulous (Figure 3–44). Denervation atrophy of the laryngeal musculature may also be identified.

Key Imaging Points

• CT imaging is the study of choice for nonmalignant disease of the larynx (eg, trauma or laryngocele); MRI more sensitively assesses cartilage invasion and more accurately delineates the transglottic spread of tumor. However, MRI of the larynx is often compromised by patient motion; therefore, thin-section contrast-enhanced CT scanning may actually provide better depiction of the extent of disease in the majority of patients.
• The subsites of the hypopharynx are often confused with those of the larynx. It is important to distinguish among them, as SCCs in these areas behave differently.
• The paraglottic and preepiglottic spaces are fat-filled compartments that are not separated from each other by fascia, so tumor can easily spread from one space to another.
• Imaging studies of the larynx in a patient with laryngeal carcinoma should always be assessed for preepiglottic and paraglottic space involvement, as well as for the status of the laryngeal cartilages, because these areas cannot be staged clinically except in far-advanced disease.
• New hoarseness in a patient with a history of head and neck cancer should prompt careful evaluation of the course of CN X (the vagus nerve) to look for tumor recurrence and spread along the carotid sheath and to the skull base.
• It is generally best to perform imaging of the larynx in quiet respiration, during which the true vocal cords are in their relaxed, abducted state. If indicated, the scan can be repeated during a maneuver such as the Valsalva maneuver to assess for paralysis or mechanical fixation.
• The thickness of soft tissue in the anterior commissure may be as much as 2 mm in patients without disease.
• The mucosal surface of the subglottis is so closely applied to the cricoid cartilage that it is generally not appreciable on the airway side of the subglottic larynx. Visible soft tissue at this level should suggest the possible presence of tumor extension.
• A submucosal tumor of the larynx most commonly represents a chondrosarcoma or a metastatic lesion.
• In the presence of a laryngocele, the larynx should be carefully assessed clinically and radiographically for the presence of a neoplasm. Even large tumors may initially present with a neck mass secondary to a laryngocele, rather than with complaints referable to the larynx (Figure 3–45).
• In the setting of trauma to the anterior neck, particularly severe blunt trauma, CT imaging is useful to assess for fracture of the laryngeal cartilages. Because it is a complete ring, the cricoid cartilage tends to fracture in two or more places.

Lymph Nodes

The cervical lymph nodes must always be carefully assessed in the setting of head and neck cancer, but cervical lymph nodes may also become involved by infectious, inflammatory, and granulomatous processes, as well as by systemic malignant neoplasms (eg, lymphoma or metastasis from primary sites other than the head and neck). Before discussing the normal appearance of the cervical lymph nodes on imaging studies and the differential diagnosis of nodal abnormalities, the appropriate terminology for the cervical lymph nodes is reviewed here. Over the last decade or so, clinical terminology has evolved from being anatomically based to a simpler classification based on levels. This classification has been translated into an imaging-based classification, which is summarized in Table 3–5 and Figure 3–46.

Some nodal groups are not included in this classification scheme, notably the retropharyngeal nodes, parotid nodes, the pre- and postauricular nodes, the facial nodes, and the suboccipital nodes. These nodes are still referred to by their anatomic names. Although these nodes may certainly be involved by neoplastic and nonneoplastic processes, they do not represent the most common sites of lymphatic spread for SCC of the upper aerodigestive tract and are not included in the level classification scheme.

On noncontrast CT scans, normal lymph nodes are ovoid, homogeneous soft tissue masses with a short-axis diameter of 5–10 mm (Figure 3–47). A fatty hilum may be recognizable as an eccentric area of low density. Pathologic lymph nodes may be enlarged and focally or diffusely hypodense if there is cyst formation or necrosis. Necrotic lymphadenopathy may be seen with SCC, treated lymphoma, and other neoplastic processes, but it may also be seen with mycobacterial infection, cat-scratch disease, and other infectious processes (Figure 3–48).

Suppurative lymphadenopathy also leads to central hypodensity. In some circumstances, a lymph node may appear hyperdense before contrast administration, usually owing to partial or complete calcification (eg, old granulomatous disease, metastatic tumoral calcification, or irradiated metastatic nodes). After contrast administration, normal lymph nodes show moderate homogeneous enhancement. Areas of cyst formation or necrosis appear hypodense and are more easily appreciated than on the noncontrast scan. In some cases, a focus of tumor may appear hyperdense to normal nodal tissue after contrast administration. This is most commonly seen with vascular metastases from thyroid or renal cell carcinoma but may also be seen with inflammatory processes. If extracapsular spread of tumor has occurred, then the node will have a poorly defined border and an irregular margin with surrounding soft tissue structures.

On MRI, normal lymph nodes are intermediate in signal intensity on T1-weighted images and hyperintense to muscle on T2-weighted images, and they show mild or moderate homogeneous enhancement postgadolinium (Figure 3–49). Fat may be identified at the nodal hilum. If a lymph node shows high signal intensity on a T1-weighted image before the administration of gadolinium, then metastatic thyroid cancer and metastatic melanoma should be considered. A cystic-appearing node may be due to infection or to tumor and will be of low signal intensity on T1-weighted images and of high signal intensity on T2-weighted images, and will show smooth peripheral enhancement postgadolinium. The neoplasms that typically result in cystic nodal metastases are SCC and thyroid carcinoma, but many primary cancers may lead to cystic-appearing nodal disease. A potential pitfall is that a single cystic metastasis may be mistaken for a benign process such as a branchial cleft cyst. Nodal necrosis due to metastatic cancer usually leads to a thick, irregular, enhancing wall and central nonenhancement. In a patient with known head and neck cancer, the presence of necrotic lymphadenopathy is considered to represent metastatic disease. In some cases of metastatic SCC, areas of abnormally low signal intensity representing keratin pools are seen on T2-weighted images.

The assessment of the cervical lymph nodes for metastatic involvement in patients with head and neck cancer is an important role for CT and MRI. Because a non-necrotic, apparently homogeneous node may still contain foci of tumor, size criteria have been developed for predicting the likelihood of metastatic nodal involvement. These criteria represent a trade-off between sensitivity and specificity, however, and depending on what cut-off is chosen for minimal axial diameter, there may be significant numbers of false-positive or false-negative nodes. The most widely accepted cut-off for reporting metastatic lymphadenopathy is a short-axis diameter ≥10 mm, but this yields a positive predictive value of only approximately 50% and a negative predictive value of approximately 80%. The development of metabolic and functional methods such as FDG PET and iron oxide–enhanced MR lymphography shows promise in improving lymph node staging, but these techniques have significant limitations in terms of their sensitivity to small foci of tumor, and the latter technique is not widely applied at present. Diffusion-weighted MRI is also gaining acceptance as a method for detecting metastatic lymph node involvement.

Spatial Approach to the Suprahyoid & Infrahyoid Head & Neck

The terminology used to describe the traditional pharyngeal subdivisions of the head and neck is best suited to the assessment and staging of SCC. Because nonsquamous masses tend to spread within fascia-defined spaces, the head and neck can also be viewed as a series of deep spaces, an approach that facilitates an analysis of cross-sectional imaging of the head and neck. To simplify the discussion, the extracranial head and neck are divided into supra- and infrahyoid compartments because fascial attachments to the hyoid bone functionally cleave this region into two segments.

Suprahyoid Head & Neck

The spaces of the suprahyoid head and neck are defined by the three layers of the deep cervical fascia: superficial (investing), middle (buccopharyngeal), and deep (prevertebral). The spaces defined by these three fascial layers are shown diagrammatically in Figure 3–50.

Pharyngeal Mucosal Space

The pharyngeal mucosal space has complex fascial margins and is not completely circumscribed by the three layers of deep cervical fascia. This space is bounded by the middle layer of deep cervical fascia along its posterolateral margin, whereas on its luminal or airway side, it has no fascial boundary. The most important components of the pharyngeal mucosal space are the squamous mucosa, the lymphoid tissue of the Waldeyer ring, the minor salivary glands, and the pharyngeal constrictor muscles. The dominant pathology in this space is SCC and the pharyngeal mucosal space, divided into its traditional subdivisions of nasopharynx, oropharynx, and hypopharynx, was reviewed previously.

Parapharyngeal Space

The parapharyngeal space (PPS) is a central, fat-filled space of the deep face that is frequently displaced by masses of the surrounding spaces (Figure 3–51). Assessing the center of a deep facial mass relative to the PPS and observing the direction in which this mass displaces the fat of this space indicates the space of origin of a mass of the head and neck and helps to tailor a differential diagnosis. The PPS is defined medially by the middle layer of the deep cervical fascia and borders the pharyngeal mucosal space. Laterally, it is defined by the superficial layer of deep cervical fascia and borders the masticator space and the parotid space. Posteriorly, the PPS is defined by the anterior part of the carotid sheath and is bordered by the carotid space. Superoinferiorly, it runs from the skull base to the hyoid bone. At its inferior extent, this space is not separated by fascia from the submandibular space, and so a process in one space may extend to the other.

The PPS contains only fat, arteries, veins, and nerves; therefore, few lesions are primary to this space. Primary lesions of the parapharyngeal space include lipomas, tumors of minor salivary rests, and atypical second branchial cleft cysts (Figure 3–52). Most lesions that appear to be primary to the PPS in fact originate from adjacent spaces and compress the PPS. Therefore, fat should be identified around the circumference of a lesion before it is said to be primary to the PPS, although peripheral fat may be difficult to identify if a lesion primary to the PPS is large. Aggressive processes that are not constrained by fascial boundaries may also involve the PPS by direct spread, notably SCC, other aggressive neoplasms (eg, sarcomas, malignant neoplasms of the salivary glands, and lymphoma; Figure 3–53), and phlegmon or abscess.

Parotid Space

The parotid space is defined by a splitting of the superficial layer of the deep cervical fascia. It abuts the masticator space anteriorly, the PPS anteromedially, the carotid space posteromedially, the temporal bone posteriorly and superiorly, and the subcutaneous fat laterally (see Figure 3–51). Its contents include the parotid gland, the facial nerve, blood vessels, and the intraparotid lymph nodes. Although the intraparotid facial nerve cannot be directly identified on cross-sectional imaging studies, it is known to lie adjacent to the retromandibular vein, and this structure serves as a rough dividing point between the superficial and deep lobes of the gland. When a mass involves both the superficial and deep lobes, the distance between the mandible and the styloid process is typically widened, especially if the mass is slow growing. The parotid duct exits the anterior aspect of the parotid space, traverses the masticator space over the masseter muscle, and then pierces the buccinator muscle to enter the oral cavity at the level of the second maxillary molar.

A differential diagnosis of parotid space masses is presented in Table 3–6, and the imaging appearance of some of the more common pathologies is discussed in more detail below. It should also be noted that the presence of multiple parotid space lesions, either unilateral or bilateral, suggests a more limited differential diagnosis that includes reactive or metastatic lymphadenopathy, lymphoepithelial lesions, Warthin tumors, and recurrent pleomorphic adenoma.

Parotid Hemangiomas

The parotid hemangioma is a vascular proliferative mass of infancy and childhood that may grow to a large size and replace the entire parotid gland before slowly involuting. The classic imaging appearance is of a multilobulated holoparotid mass that enlarges the parotid gland, is isointense to muscle on a T1-weighted image, is bright on a T2-weighted image, and enhances intensely and homogeneously postgadolinium (Figure 3–54). It usually contains prominent flow voids, and the external carotid artery and its branches are often enlarged.

First Branchial Cleft Cysts

Abnormalities of the first branchial apparatus account for less than 10% of branchial complex anomalies and include cysts, sinuses, and fistulas. Typically, a cystic mass is seen within or adjacent to the parotid gland (Figure 3–55), with a tract leading to the external auditory canal visible in some cases. The cyst wall may be thickened if there has been prior infection, and adjacent soft tissues may show inflammatory change if there is active infection.

Lymphoepithelial Cysts and Lesions

Benign lymphoepithelial lesions are seen most commonly in association with HIV, but they also occur in connective tissue disorders, notably Sjögren syndrome. In the setting of HIV, there is typically associated hypertrophy of the lymphoid tissue of Waldeyer ring (Figure 3–56) and also reactive cervical lymphadenopathy. Lesions may be purely cystic or have both cystic and solid elements, and they are typically bilateral.

Parotitis and Calculus Disease

Glandular enlargement, edema, and increased enhancement are seen in the setting of acute parotitis, often with inflammatory changes in adjacent fat (Figure 3–57). If the process progresses to abscess formation, a ring-enhancing mass will be present. A calculus may be identified along the parotid duct or within the gland, best detected on thin-section (1–3 mm) noncontrast CT images. The intra- or extraparotid glandular system may be dilated.

Pleomorphic Adenomas

The pleomorphic adenoma typically presents as a round or ovoid, well-circumscribed soft tissue mass. It may have areas of low density on CT and is typically high signal intensity on T2-weighted MRI caused by areas of mucoid matrix or cystic degeneration (Figure 3–58). Contrast enhancement is usually intense and homogeneous, and the homogeneity typically increases over time when early and delayed postcontrast CT images are compared.

Warthin Tumor

A Warthin tumor is typically multilobulated, well circumscribed, and heterogeneous owing to its mixed cystic and solid nature (Figure 3–59). Areas of hemorrhage may be seen as well, and bilateral lesions are not uncommon.

Malignant Parotid Tumor

A low-grade malignant parotid tumor may appear well circumscribed and homogeneous and, based on imaging criteria, can be difficult to distinguish from a benign lesion such as a pleomorphic adenoma. Malignant tumors do, however, tend to be somewhat lower in signal intensity on T2-weighted images than benign lesions. Higher-grade lesions are often ill marginated (Figure 3–60) and invade adjacent structures such as the temporal bone, adjacent fat, and the muscles of mastication. They may also demonstrate perineural spread proximally along the facial nerve (Figure 3–61). Note that a pregadolinium T1-weighted image may be the best sequence on which to identify a parotid mass as the fatty glandular parenchyma contrasts well with the intermediate signal intensity of most parotid neoplasms (Figure 3–62).

Masticator Space

The masticator space is defined by a splitting of the superficial layer of deep cervical fascia. Its coronal extent is from the inferior surface of the mandible to the skull base medially and the calvarial convexity laterally. Superomedially, the fascia attaches to the skull base just medial to the foramen ovale; superolaterally, it attaches to the zygomatic arch and then continues superiorly over the surface of the temporalis muscle, defining the suprazygomatic masticator space (Figure 3–63). The masticator space is bordered by the parapharyngeal space medially, the parotid space posteriorly, and the subcutaneous tissues laterally. Anteriorly, it abuts the buccal space. The buccal space has no true fascial boundary and is in close proximity to the masticator space, so these two spaces are often involved together by infectious or neoplastic processes. Key contents of the masticator space include the ramus and the posterior body of the mandible, the muscles of mastication (eg, the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles), the motor and sensory branches of the third division of the trigeminal nerve, and the inferior alveolar vein and artery.

Lesions of the masticator space (Table 3–7) are most commonly infectious (usually of odontogenic origin) or neoplastic. In all cases of neoplastic involvement of the masticator space, V3 should be carefully assessed for evidence of perineural spread of tumor. Perineural spread, when radiologically visible, may lead to the enlargement of V3 and the foramen ovale (Figure 3–64), the asymmetric enhancement of V3 (which may extend back along the main trunk of V3 to the pons), the obliteration of fat at the extracranial aperture of the foramen ovale, and possibly the replacement of CSF in Meckel cave by abnormal soft tissue. In addition, denervation change in the muscles of mastication may be seen. In the acute and subacute phases of denervation, the muscles typically demonstrate high signal intensity on T2-weighted images and enhancement on postgadolinium images, whereas in the more chronic phase, fatty atrophy sets in (Figure 3–65). Several “pseudomasses” of the masticator space should also be considered. Benign masseteric hypertrophy may be unilateral or bilateral and is generally seen in patients with bruxism. Accessory parotid tissue may also be unilateral or bilateral, is seen overlying the masseter muscle, and is isodense or isointense to a normal parotid gland on all imaging sequences. Denervation atrophy due to V3 injury or pathology may make the contralateral nonatrophic muscles appear masslike.

The buccal space is not a true fascia-defined compartment. It is located immediately anterior to the masticator space and is often involved by extension of neoplastic or inflammatory processes from the masticator space. Important contents include the buccal fat pad, the buccinator muscle, the distal portion of the parotid duct, and the facial artery and vein. Venous malformations of the head and neck not uncommonly involve the buccal space (Figure 3–66).

Odontogenic Infection

Patients with an odontogenic infection usually have a history of poor dentition or recent dental manipulation. CT scanning is the study of choice and may show changes related to periodontal disease, frank mandibular osteomyelitis, and adjacent soft tissue changes with cellulitis, phlegmon, and/or abscess formation (Figure 3–67). CT scanning is more sensitive than MRI to calculi, foreign bodies, and gas formation.

Rhabdomyosarcoma

A solid mass lesion arising in the masticator space of a child is considered a rhabdomyosarcoma until proven otherwise. These lesions may appear fairly well circumscribed, although they are aggressive. They are typically isointense to muscle on T1-weighted images and intermediate in signal intensity on T2-weighted images, as is typical of small, round, blue-cell tumors owing to their high nuclear-to-cytoplasmic ratio. Postgadolinium, they enhance homogeneously or heterogeneously if areas of necrosis are present (Figure 3–68). There may be accompanying destruction of the mandible, and spread to the skull base and intracranial compartment may occur.

Carotid Space

All three layers of the deep cervical fascia contribute to the fascial boundary of the carotid space, known as the carotid sheath. The carotid space extends from the skull base to the aortic arch, and therefore spans both the supra- and the infrahyoid neck. At the level of the skull base, the carotid space communicates directly with the carotid canal and jugular foramen. The suprahyoid carotid space relates laterally to the parotid space, anteriorly to the parapharyngeal space, and medially to the retropharyngeal space. Posteriorly, it borders the vertebral bodies of the cervical spine.

The contents of the carotid space include the carotid artery (common or internal, depending on the level), the internal jugular vein, the sympathetic plexus, and cranial nerves (Figure 3–69). The upper (nasopharyngeal) carotid space contains CN IX (the glossopharyngeal nerve), X (the vagus nerve), XI (the accessory nerve), and XII (the hypoglossal nerve). Only CN X traverses the oropharyngeal and infrahyoid carotid space, since the other lower cranial nerves have already exited the carotid space. CN X is typically located posteriorly between the carotid artery and the internal jugular vein, whereas the sympathetic plexus runs along the medial aspect of the carotid space. Lymph nodes are also present in the carotid space, with the highest carotid space nodes constituting the jugulodigastric nodes—or, more correctly, the upper level IIA nodes. The most common lesions of the carotid space are vascular or neoplastic. “Pseudomasses” are typically vascular in origin and relate to the asymmetry or tortuosity of the carotid artery or the asymmetry of the jugular veins. Common lesions of the carotid space are indicated in Table 3–8.

Paragangliomas

Paragangliomas arise from neuroendocrine cells of the autonomic nervous system. In the head and neck, subtypes include the carotid body tumor, the glomus vagale (arising from the nodose ganglion of the vagus nerve), the glomus jugulare (arising from the jugular ganglion), and the glomus tympanicum (arising in association with the Jacobsen nerve along the cochlear promontory). These lesions may present as a palpable neck mass or with lower cranial neuropathy, pulsatile tinnitus, or both. On CT scans, these lesions enhance intensely postcontrast. The glomus jugulare typically causes irregular erosion of adjacent bone. On MRI, paragangliomas typically show macroscopic flow voids when they are >2 cm and also show intense enhancement. The carotid body tumor classically splays the internal and external carotid arteries (Figure 3–70), whereas the glomus vagale displaces the internal carotid artery anteriorly (Figure 3–7l). MRA and catheter angiography demonstrate a hypervascular mass, with the usual vascular supply being the ascending pharyngeal artery.

Schwannomas

Schwannomas of the lower cranial nerves may be asymptomatic and present as a neck mass or incidental finding on an imaging study obtained for another purpose, or may present with lower cranial neuropathy. On imaging, these lesions are typically round or ovoid and well circumscribed (Figure 3–72). Adjacent bony structures may be smoothly remodeled but do not show infiltrative or permeative changes. Schwannomas may be homogeneous or heterogeneous owing to cyst formation and hemorrhage. They are typically moderately and homogeneously enhancing. Rarely, macroscopic flow voids may be seen in “hypervascular” schwannomas, making them difficult to distinguish from paragangliomas.

Squamous Cell Carcinoma

SCC may access the carotid space via direct invasion from the primary site or via nodal metastases. A primary squamous carcinoma of the upper aerodigestive tract may be deeply infiltrative at the time of the first diagnosis, extending to involve the carotid artery and thereby rendering the tumor unresectable without carotid sacrifice; more commonly, recurrent disease at the primary site may infiltrate adjacent deep tissues and extend back to the carotid space. Metastases to the lymph nodes along the jugular vein (levels II, III, and IV) are common with mucosal SCCs, and if there is extracapsular extension, then the metastatic tumor may extend all the way to the skull base along the carotid sheath (Figure 3–73). New hoarseness or difficulty with articulation may be seen if CN X or XII is affected by metastatic tumor in the carotid space, and these symptoms should raise concern for recurrent disease in a patient previously treated for SCC.

Lesions of the Sympathetic Chain

The cervical segment of the sympathetic trunk extends from the base of the skull down to the first rib, where it becomes continuous with the thoracic segment. The cervical sympathetic chain lays posteromedial to the internal and common carotid arteries and is embedded in the deep fascia between the carotid sheath and the prevertebral fascia. Neuroblastic tumors are the third most common cause of early childhood neoplasia, and lesions originating from the cervical sympathetic chain account for 2–5% of neuroblastic lesions. There are three histologic subgroups, neuroblastoma, ganglioneuroblastoma, and ganglioneuroma, with neuroblastoma being the least differentiated and most malignant form. A helpful diagnostic clinical feature may be the presence of Horner syndrome (Figure 3–74).

Retropharyngeal Space

The retropharyngeal space is a potential space between the middle and deep layers of the deep cervical fascia that extends from the skull base to the T4 level (Figure 3–75). Anatomically, a slip of deep cervical fascia separates the retropharyngeal space from a more posterior potential space known as the “danger space,” which extends more caudally into the mediastinum and provides a conduit to this space for disease processes, notably infection. For practical purposes, however, the retropharyngeal and danger spaces are indistinguishable on imaging studies of the neck, and both are included when the retropharyngeal space is discussed. The retropharyngeal space is bordered by the pharyngeal mucosal space anteriorly, the carotid space laterally, and the danger space and prevertebral space posteriorly. The only notable contents of the retropharyngeal space are fat and lymph nodes; therefore, the retropharyngeal space is usually affected by the direct spread of tumor or infection or by the spread of tumor or infection to retropharyngeal lymph nodes. The extension of tumor beyond the confines of a retropharyngeal node may lead to skull base invasion and lower cranial nerve dysfunction, whereas the extension of infection beyond the nodal capsule may lead to retropharyngeal abscess formation.

The lateral retropharyngeal nodes are present at the level of the nasopharynx and upper oropharynx and are seen well on MRI even when nondiseased (Figure 3–76). The medial retropharyngeal nodes are present from the nasopharynx to the hypopharynx, but retropharyngeal nodes are not usually found below the level of the hyoid bone. Retropharyngeal lymph nodes are normally quite prominent in children and gradually decrease in size. In adults, normal retropharyngeal nodes are typically <6 mm in short-axis dimension.

Pyogenic Infection

Retropharyngeal nodes are commonly involved with infection in the context of pharyngitis in children and spine infections in adults. With infection, the nodes initially enlarge and may eventually suppurate. As the infection progresses, the retropharyngeal fat becomes edematous because of retropharyngeal cellulitis, and if the nodal capsule ruptures, then a retropharyngeal abscess develops (Figure 3–77). A CT scan should be performed if there is concern for a retropharyngeal abscess, since these patients generally require surgical drainage and intravenous antibiotics. In some cases, the retropharyngeal space may simply be filled with noninfected fluid (retropharyngeal edema) owing to jugular venous or lymphatic obstruction, prior radiation therapy, or noninfectious inflammatory processes; it is therefore important to distinguish retropharyngeal edema from retropharyngeal infection (Figure 3–78), as this will influence patient management.

Neoplasms

Retropharyngeal nodal metastases are most commonly seen with nasopharyngeal carcinoma and with SCC of the posterior oropharyngeal wall and hypopharynx. Non-Hodgkin lymphoma of the Waldeyer ring also commonly leads to neoplastic enlargement of the retropharyngeal nodes. The retropharyngeal space may also be involved with direct extension of a primary tumor from the pharyngeal mucosal space, the carotid space, or the vertebral column and perivertebral space.

Perivertebral Space

The space around the spinal column has generally been referred to as the prevertebral space, but an argument has been made to adopt the more encompassing term perivertebral space. Within the perivertebral space, enclosed and defined by the deep layer of deep cervical fascia, two regions can be recognized: the prevertebral and the paraspinal portions of the perivertebral space. The prevertebral portion is defined by the deep layer of the deep cervical fascia as it arches from one transverse process to the other transverse process in front of the vertebral body, enclosing the prevertebral muscles as well as the vertebral artery, the vertebral vein, and the vertebral body. The paraspinal portion is defined by the deep layer of deep cervical fascia, extending back on each side from the transverse process to the nuchal ligament in the midline; it therefore includes only the paraspinal muscles, the posterior elements of the vertebra, and fat. The prevertebral portion of the perivertebral space is bordered by the retropharyngeal and danger spaces anteriorly and the carotid space anterolaterally. A mass in the prevertebral portion of the perivertebral space displaces the retropharyngeal space anteriorly; if the lesion is primary to the vertebral body, it also displaces the prevertebral muscles anteriorly, confirming its localization to the prevertebral portion of the perivertebral space.

The perivertebral space is most commonly involved by infectious processes originating from the vertebral bodies and the intervertebral discs (Figure 3–79), and neoplasia of the spinal column—most commonly metastatic disease, but also primary bone tumors and hematologic processes such as leukemia and myeloma (Figure 3–80). Because the deep layer of the deep cervical fascia is very tough and resists violation by tumor and infection, it is unusual for retropharyngeal space processes to extend into the perivertebral space, and vice versa.

The Posterior Cervical Space

The posterior cervical space has complex fascial margins and is defined by both superficial and deep layers of the deep cervical fascia. It extends from the skull base to the clavicle, spanning the supra- and infrahyoid neck, but having a relatively small suprahyoid segment. It abuts the carotid space anteriorly, the perivertebral space medially, and the sternocleidomastoid muscle and subcutaneous fat laterally. Its suprahyoid contents include fat, CN XI, and lymph nodes in levels II and V. Pathology in the posterior cervical space is most commonly nodal (Figure 3–81).

Infrahyoid Neck

As in the suprahyoid neck, the infrahyoid neck is cleaved into a series of spaces by the three layers of the deep cervical fascia. These spaces are illustrated in Figure 3–82. There are five major spaces of the infrahyoid neck, four of which also traverse the suprahyoid neck, and their suprahyoid segments have already been discussed: the carotid space, the retropharyngeal space, the perivertebral space, and the posterior cervical space. Only the visceral space is unique to the infrahyoid neck.

Visceral Space

The visceral space extends from the hyoid bone to the mediastinum, and its circumference is defined by the middle layer of deep cervical fascia. This complex space contains the thyroid and parathyroid glands, the larynx and trachea, the hypopharynx and esophagus, the recurrent laryngeal nerves, and visceral (level VI) lymph nodes.

Infrahyoid Carotid Space

The infrahyoid carotid space includes the common carotid artery, the internal jugular vein, the vagus nerve, and the sympathetic chain. Level III and IV lymph nodes are intimately associated with the infrahyoid carotid space, although they do not lie within the fascial boundaries of this space. The infrahyoid carotid space apposes the visceral space anteromedially, the perivertebral space posteromedially, and the posterior cervical space posterolaterally.

Infrahyoid Posterior Cervical Space

As in the suprahyoid neck, the infrahyoid posterior cervical space has complex fascial boundaries derived from the superficial and deep layers of the deep cervical fascia, as well as the posterior aspect of the carotid sheath. It contains primarily fat and lymph nodes, but the trunks of the brachial plexus also traverse the posterior cervical space. This space is most commonly involved with nodal pathology.

Infrahyoid Retropharyngeal Space

The only significant difference between the supra- and infrahyoid retropharyngeal space is that the infrahyoid retropharyngeal space contains only fat, whereas the suprahyoid retropharyngeal space also contains lymph nodes. There are, therefore, almost no processes that are primary to the infrahyoid retropharyngeal space, except, occasionally, lipoma. Pathology in the retropharyngeal space, whether inflammatory, infectious, or neoplastic, accesses this space either by direct extension from adjacent spaces across fascial boundaries or by inferior extension of a process centered in the suprahyoid retropharyngeal space.

Infrahyoid Perivertebral Space

The infrahyoid perivertebral space also occurs as two distinct areas, the prevertebral and the paraspinal portions of the perivertebral space, which are enclosed by the deep layer of deep cervical fascia. In the infrahyoid neck, in addition to the prevertebral muscles and vertebral vessels, the prevertebral portion of the perivertebral space contains the phrenic nerve, the scalene muscles, and the roots of the brachial plexus. The roots of the brachial plexus actually pierce the deep layer of deep cervical fascia on their way to the posterior cervical space.

Trans-Spatial Masses

Some pathologies classically involve multiple spaces and can be considered within a unique group of multispatial or “trans-spatial” processes. These are typically lesions of structures that normally pass from one space to another, such as blood vessels, lymphatics, and nerves. Although aggressive infectious or neoplastic processes may also traverse spatial boundaries, they do so by virtue of their destructive nature rather than as a consequence of the tissue of origin. The entities that commonly present as trans-spatial processes include capillary hemangiomas, vascular malformations (venous or arteriovenous), lymphatic malformations, and plexiform neurofibromas. The latter are typically seen in patients with neurofibromatosis type I.

The soft tissue vascular lesions of the head and neck fall into two categories: hemangiomas and vascular malformations. The term hemangioma should be limited to vascular lesions of infancy, which grow rapidly in early infancy and then undergo fatty replacement and involution by adolescence. Vascular malformations result from abnormal blood or lymphatic vessel morphogenesis and are classified by the predominant type of vessel involved (ie, capillary, venous, lymphatic, or arteriovenous malformations).

Hemangiomas are typically intermediate signal intensity on T1-weighted images and bright on T2-weighted images, and enhance intensely postgadolinium (see Figure 3–54, parotid hemangioma). Flow voids may be seen within larger lesions, and feeding arteries may be enlarged. As hemangiomas involute, they may show an increasingly high signal on T1-weighted images due to fatty replacement. In patients with a large, segmental, plaque-type facial hemangiomas, PHACES syndrome should be considered. PHACES is an acronym coined to describe a neurocutaneous syndrome that encompasses the following features: posterior fossa brain malformations, large facial hemangiomas, arterial cerebrovascular anomalies, cardiac anomalies and aortic coarctation, eye anomalies, and ventral developmental defects (sternal defects or supraumbilical raphe). Children at risk should receive careful ophthalmologic, cardiac, and neurologic assessments. Venous malformations have signal characteristics similar to hemangiomas, but they are typically multilobulated and contain venous lakes and also rounded calcifications (phleboliths). (See Figure 3–66, venous malformation of the buccal space.) Venous malformations are not high-flow lesions and do not demonstrate enlargement of feeding vessels or draining veins, or internal flow voids. Lymphatic malformations are discussed later in this chapter in Cystic Neck Masses. Arteriovenous malformations have serpiginous signal voids and lack a dominant mass (Figure 3–83).

Thyroid & Parathyroid

Thyroid

The thyroid gland consists of right and left lobes connected across the midline by a narrow isthmus. A pyramidal lobe is frequently present, projecting upward from the isthmus and in some cases connecting to the hyoid bone via a fibrous or muscular band. The thyroid is a highly vascular organ that is supplied mainly by the superior and inferior thyroid arteries, the former being a branch of the external carotid artery and the latter a branch of the thyrocervical trunk. Because of its high iodine concentration, the thyroid gland is intrinsically dense on a noncontrast CT scan (Figure 3–84). Following the administration of iodinated contrast material or gadolinium, the normal thyroid gland enhances homogeneously (Figure 3–85).

Nonspecific, incidental thyroid lesions such as cysts and adenomas are very commonly seen on cross-sectional imaging studies. The primary evaluation of a thyroid mass is typically done with ultrasound and nuclear medicine scanning, with CT scanning or MRI reserved to assess the extent of a process and evaluate the rest of the neck. If there is a concern about possible thyroid carcinoma, then the cross-sectional imaging evaluation should be done with a noncontrast CT scan or, ideally, gadolinium-enhanced MRI. Because the thyroid gland concentrates iodine, the bolus of iodinated contrast material that is given during a CT scan of the neck can take many months to clear from a patient's system and can delay radioiodine therapy for as long as 6 months.

Benign Thyroid Lesions

Benign thyroid lesions include goiter, colloid cyst, and adenoma. The goiter appears on the CT scan or MRI as a diffuse or multinodular enlargement of the gland, often with areas of heterogeneous density on CT scan and intensity on MRI. Dramatic enlargement of the gland may result in the displacement and compression of vital structures such as the trachea (Figure 3–86). A colloid cyst is a well-circumscribed cystic lesion that may appear bright on a pregadolinium T1-weighted image owing to an elevated protein content or hemorrhagic contents. A thyroid adenoma is a generally well-circumscribed mass that may have areas of calcification, hemorrhage, or cystic degeneration within it; adenomas are indistinguishable from low-grade thyroid carcinomas on the basis of imaging alone.

Thyroid Carcinoma

Thyroid carcinoma has a number of pathologic subtypes that are generally not distinguishable from one another on imaging studies (Figure 3–87). Less aggressive carcinomas generally present as well-circumscribed masses, whereas more aggressive lesions such as anaplastic carcinomas are highly invasive and destructive of adjacent tissues. Of note, the nodal metastases of thyroid carcinoma may appear cystic, and metastatic thyroid cancer should be included in the differential diagnosis of a cystic neck mass. Because these nodal metastases may be either hemorrhagic because of the highly vascular nature of thyroid cancer or highly proteinaceous because of their thyroglobulin content, they may show a high signal intensity on a pregadolinium T1-weighted image (Figure 3–88). This appearance is highly suggestive of metastatic thyroid cancer.

Parathyroid

The parathyroid glands are ovoid bodies measuring approximately 6 mm in length that are intimately related to the posterior border of the thyroid gland and lie within its fascial capsule. There are typically two superior and two inferior parathyroid glands, but in some cases, a parathyroid gland may be found some distance caudal to the gland, in association with the inferior thyroid veins or even in the superior mediastinum. Parathyroid pathology is most commonly assessed with ultrasound and with nuclear medicine scanning (sestamibi). The normal glands are usually not identified on a CT scan or MRI and are identified only when pathologically enlarged, typically by parathyroid adenoma. A pathologically enlarged parathyroid gland may look very similar to a lymph node on a CT scan, but on MRI, the parathyroid adenoma is typically high in signal on T2-weighted images, which is a helpful feature.

Cystic Neck Masses

The identification of a neck mass as cystic presents a limited differential diagnosis and often permits the differential considerations to be narrowed to a list of one or several entities when the specific clinical, CT, and/or MRI features are taken into consideration. A list of the more common cystic neck masses is presented in Table 3–9. To be considered in this differential, a mass should be of fluid density or intensity and lack enhancement. The mass should have a thin, regular rim, although prior infection may lead to thickening of the wall and the presence of enhancement. It is important to note that hemorrhage into a cyst or increased protein content within a cyst may affect its density or intensity. Some lesions that are not truly cystic may mimic a cystic neck mass because of central nonenhancement—notably, a thrombosed jugular vein, a thrombosed aneurysm or pseudoaneurysm, or a necrotic mass with a nonenhancing center.

Pathology

Branchial Cleft Cysts

The second branchial apparatus accounts for ∼90% of all branchial cleft anomalies. On a CT scan or MRI, a unilocular cystic mass is seen displacing the submandibular gland anteromedially and the sternocleidomastoid muscle posterolaterally (Figure 3–89). In some cases, a “beak” pointing between the internal and external carotid arteries will be identified, and very rarely, a tract leading to the tonsillar fossa will also be identified. A sinus tract or fistula extending inferiorly in the neck to drain just above the clavicle may also be identified (Figure 3–90). If infection has occurred in the past, the cyst wall may show thickening and enhancement. If the infection is active, there may also be inflammatory changes in adjacent soft tissues.

Thyroglossal Duct Cysts

During embryogenesis, the thyroid anlage descends from the level of the foramen cecum at the tongue base to its normal position in the infrahyoid neck. Thyroid elements may remain at any level along this pathway (the thyroglossal duct) and may give rise to cysts, fistulas, or solid nodules of thyroid tissue. Thyroglossal duct cysts are usually located at or just below the hyoid bone, in which case a midline or paramedian cystic mass that is embedded in the strap muscles is seen (Figure 3–91). There is typically no associated enhancement unless prior or active infection has occurred. In some cases, carcinoma may arise within a thyroglossal duct cyst; clues to this include the presence of calcification and solid tissue components.

Lymphatic Malformations

Lymphatic malformations, also known as cystic hygromas or lymphangiomas, result from the maldevelopment of lymphatic vessels and the failure of these abnormal vessels to communicate with normal lymphatic drainage channels. This leads to a fluid-filled mass that is characteristically multilobulated and multiloculated. The lymphatic malformation may involve multiple spaces, but most commonly involves the posterior cervical space. These lesions are typically of low density on CT scans, but are often heterogeneous in signal intensity on T1- and T2-weighted MRI sequences because of their variable protein content and their propensity to hemorrhage. In fact, fluid–fluid levels due to hemorrhage are characteristic of lymphatic malformations (Figure 3–92). Lymphatic malformations do not enhance postcontrast, although fibrous septa separating fluid spaces may normally enhance and the lesion may demonstrate peripheral enhancement if infection has occurred.

Epidermoid and Dermoid Lesions

Dermoid and epidermoid lesions result from the sequestration of ectodermal tissue. In the head and neck, they most commonly occur in the floor of mouth (Figure 3–93). Both are lined by squamous epithelium, but the dermoid also contains skin appendages (eg, sebaceous glands and hair follicles) within its wall. These lesions are typically midline, unilocular, and slowly growing. Both contain cheesy material due to desquamated keratin, but the dermoid may contain fatty material as well. Epidermoids are typically low density on CT scans, low signal intensity on T1-weighted images, and high signal intensity on T2-weighted images—hence, their “fluidlike” appearance. The rim of the lesion may enhance postcontrast. Dermoids are similar in appearance except that their fatty contents may result in a very low density on CT scans and a high signal on T1-weighted MRI.

Foregut Cysts

Foregut cysts are uncommon congenital defects of the developing airway and gut that may occur anywhere from the mouth to the anus. They are relatively rare in the neck, but may present with a neck mass or, if large, with airway obstruction or compression of other vital structures. The imaging is nonspecific (Figure 3–94), although there is often high signal within the cyst fluid on a T1-weighted image owing to an elevated protein content. These lesions tend to be located in the low neck and may extend into the superior mediastinum.

Ranulas

The simple ranula is a mucous retention cyst that is confined to the floor of mouth and is presumed to be caused by the obstruction of a sublingual gland. In some cases, there is a rupture of the capsule or pseudocapsule and extension into the neck, and the lesion is then referred to as a plunging or diving ranula. This extension to the neck may occur along the deep lobe of the submandibular gland, between the mylohyoid and hyoglossus muscles, or via a congenital dehiscence in the mylohyoid muscle itself. A simple ranula appears as a unilocular cyst in the floor of mouth on both CT scans (see Figure 3–26) and MRI and may be difficult to distinguish on imaging from an epidermoid or a lymphangioma. A plunging ranula usually shows a “tail” leading back to the sublingual space, which is very suggestive of the diagnosis.

Laryngoceles

A laryngocele develops when the laryngeal ventricle or its appendix is functionally or anatomically obstructed. The mass that develops may be filled with air, fluid, or pus. The internal laryngocele is confined to the paralaryngeal space, whereas the external laryngocele penetrates the thyrohyoid membrane and may present as a neck mass. The imaging characteristics depend on the laryngocele contents (see Figures 3–41 and 3–45). In all cases, the larynx should be closely inspected clinically and on imaging studies to assess for a causative obstructing lesion.

The Pediatric Neck

The imaging evaluation of the pediatric neck raises a limited differential diagnosis, which is heavily weighted toward congenital-developmental and infectious-inflammatory processes, but also includes a limited list of neoplastic or neoplasm-like considerations. A differential diagnosis of the more common pediatric neck masses is presented in Table 3–10. The appropriate imaging workup of neck masses depends on the category of disease. Infectious-inflammatory processes are typically evaluated with CT scanning, with MRI reserved to assess complications such as spinal epidural or intracranial extension. Congenital and neoplastic processes are most completely assessed with MRI, which may also provide more specificity regarding a particular diagnosis; however, a good-quality, thin-section, contrast-enhanced CT scan may also be adequate for many of these lesions. In general, a child under the age of 5 requires monitored anesthesia care or general anesthesia for CT scanning or MRI to obtain a high-quality study. Over the age of 5, many CT studies can be done without sedation, but most children are not able to cooperate with a more lengthy MRI study without sedation until at least age 8 or 10.

Fibromatosis Colli

This benign disorder presents as torticollis or as a palpable neck mass in neonates and young infants. Because of its association with traumatic delivery, it is thought to be related to perinatal muscle trauma with a fibroinflammatory response within the sternocleidomastoid muscle. Imaging features are nonspecific but characteristic. On ultrasound, the mass is fusiform, expanding the belly of the sternocleidomastoid muscle and tapering at the ends; it is noncalcified and varied in its echogenicity. On MRI, the mass is similarly fusiform and oriented along the course of the sternocleidomastoid muscle. It is intermediate in signal intensity on T1-weighted images and heterogeneous on T2-weighted images, and it demonstrates enhancement postgadolinium (Figure 3–95). The adjacent soft tissues are normal, and there is no associated lymphadenopathy. Its appearance is characteristic, but the clinical and imaging differential diagnosis of fibromatosis colli includes rhabdomyosarcoma.

Paranasal Sinuses & Nasal Cavity

Paranasal Sinuses

The paranasal sinuses and nasal cavity are well suited to assessment by thin-section (≤3 mm) coronal CT imaging, which clearly delineates the delicate bony anatomy of this region (Figure 3–96). The paired maxillary sinuses lie on either side of the nasal cavity, with the orbit above, the maxillary alveolus below, and the pterygopalatine fossa behind. Drainage is via the maxillary ostium into the infundibulum. The ethmoid sinus is a series of air cells, usually divided into anterior, middle, and posterior air cells, which are intimately related to the orbit laterally and the anterior cranial fossa superiorly. The roof of the ethmoid, also known as the fovea ethmoidalis, forms part of the floor of the anterior cranial fossa and lies just lateral and superior to the cribriform plate (the roof of the nasal cavity). Drainage of the anterior and middle ethmoid air cells is into the middle meatus, whereas the posterior ethmoid air cells drain via the sphenoethmoidal recess. The frontal sinuses abut the orbit inferiorly and the anterior cranial fossa posteriorly. They drain via the nasofrontal “duct” into the frontal recess of the middle meatus. The sphenoid sinuses arise from the body of the sphenoid bone and are intimately associated with the structures of the central skull base: the sella turcica above, the cavernous sinuses laterally, and the nasopharynx inferiorly. Drainage is via the sphenoethmoidal recess into the superior meatus (Figure 3–97).

Ostiomeatal Unit of the Nasal Cavity

The lateral nasal wall is anatomically complex. The superior, middle, and inferior turbinates project from the lateral nasal wall, and each overlies its respective meatus (Figure 3–98). The inferior turbinate arises from the junction of the uncinate process and the medial wall of the maxillary sinus, and the inferior meatus lies medial to it. The ostium of the nasolacrimal duct opens into the inferior meatus. The middle turbinate has more complex attachments, with a superior attachment to the cribriform plate, a lateral attachment to the lamina papyracea, and a posterior attachment to the ethmoid crest of the palatine bone. The maxillary sinuses, anterior and middle ethmoid air cells, and frontal sinuses drain into the middle meatus. The superior turbinate attaches to the skull base superiorly (often merging with the attachment of the middle turbinate), the lamina papyracea laterally, and the inferior portion of the anterior wall of the sphenoid sinus posteriorly. The superior meatus receives drainage from the posterior ethmoid air cells.

The ostiomeatal unit includes the maxillary ostium and the structures of the middle meatus, and defines the region into which the frontal, anterior, and middle ethmoid and maxillary sinuses drain. When the ostiomeatal unit is diseased, a characteristic pattern of obstructive sinus disease is present, with involvement of the aforementioned areas.

Important components of the ostiomeatal unit that are well visualized on coronal CT scans include the infundibulum, the uncinate process, and the ethmoid bulla (Figure 3–99). The infundibulum is a channel defined by the orbital wall laterally, the uncinate process medially, and the ethmoid bulla superiorly; it connects superomedially to the hiatus semilunaris and functions as the conduit for secretions from the maxillary and ethmoid sinuses. The uncinate process is the thin, hook-shaped bony process that forms the medial wall of the infundibulum. The ethmoid bulla receives drainage from the middle ethmoid air cells.

Anatomic Variations

The concha bullosa or pneumatized middle turbinate is seen commonly on screening CT scans of the sinus (Figure 3–100). Usually an incidental finding, a large concha bullosa may encroach on the infundibulum or become primarily diseased with mucosal inflammation, polyps, or mucocele formation (Figure 3–101). The middle turbinate may be paradoxically curved and the uncinate process may deviate medially or laterally or may be pneumatized. Variations in ethmoid air cells are also common, notably the presence of infraorbital ethmoid air cells (so-called Haller cells, Figure 3–102) and agger nasi cells, which are extensions of anterior ethmoid air cells into the lacrimal bone.