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.
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.
Diagrammatic representation of the fascia-defined spaces of the suprahyoid neck at the level of the nasopharynx. The dashed line represents the deep layer of deep cervical fascia, also known as the prevertebral fascia. The dotted line represents the middle layer of deep cervical fascia, and the thick solid line represents the superficial layer of deep cervical fascia, also known as the investing fascia. The heavy solid line outlining the pharyngeal mucosal space represents the pharyngobasilar fascia, which connects the superior constrictor muscle to the skull base. PMS, pharyngeal mucosal space; PPS, parapharyngeal space; MS, masticator space; PS, parotid space; CS, carotid space; RPS, retropharyngeal space; PVS, perivertebral space; BS, buccal space. (Note that the buccal space does not represent a true fascia-defined space, but is often considered as a distinct space for the purposes of anatomic localization and differential diagnosis.) (Modified and reproduced, with permission, from Harnsberger HR. CT and MRI of masses of the deep face. Curr Probl Diagn Radiol 1987;16:141.)
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.
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.
Axial T1-weighted image demonstrates high signal intensity fat in the centrally located parapharyngeal space (PPS). Also indicated is the parotid space (PS).
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.
Axial contrast-enhanced CT scan demonstrates a well-circumscribed cystic lesion (*) centered on the right parapharyngeal space, deviating the airway and the pharyngeal mucosal space medially and displacing the muscles of mastication laterally. The normal left parapharyngeal space is indicated. The pathology was most consistent with a branchial cleft cyst. Ma, masseter; M, mandible; Mp, medial pterygoid; PPS, parapharyngeal space.
Axial T1-weighted image in a patient with lymphoma demonstrates a left oropharyngeal mass with lateral extension to obliterate the parapharyngeal fat. The normal right tonsil (T) and right parapharyngeal space (PPS) are shown for comparison. Masseter (Ma), medial pterygoid muscle (MP), and parotid gland (P) are indicated.
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.
Table 3–6. Lesions of the Parotid Space. ||Download (.pdf)
Table 3–6. Lesions of the Parotid Space.
|Hemangioma||Parotitis or parotid abscess||Pleomorphic adenoma||Mucoepidermoid carcinoma|
|Venolymphatic malformation||Reactive lymphadenopathy||Warthin tumor||Adenoid cystic carcinoma|
|First branchial cleft cyst||Lymphoepithelial cysts or lesions||Lipoma||Acinic cell carcinoma|
|Facial nerve schwannoma||Carcinoma ex pleomorphic adenoma|
|Oncocytoma||Salivary ductal carcinoma|
|Squamous cell carcinoma|
|Extranodal or nodal non-Hodgkin lymphoma|
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.
(A) Axial T1-weighted image in a 13-month-old female with a parotid region mass and overlying skin discoloration demonstrates a large, multilobulated, well-circumscribed mass centered on the parotid gland. Internal serpiginous hypointensities (arrowheads) are consistent with vessels. The contralateral parotid gland (P) is shown for comparison; note that the parotid gland in an infant and young child is not as fatty as in an adult and therefore not as bright on a T1-weighted image. (B) The mass is high in signal intensity on a T2-weighted image. Again, note the prominent vessels within the lesion. Postgadolinium (not shown), the lesion demonstrated intense and homogeneous enhancement. These imaging features are diagnostic of a parotid hemangioma.
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.
A 3-year-old girl with a left parotidregion mass and slight drainage from her external ear canal. Axial fast spin-echo T2-weighted image with fat saturation demonstrates a well-circumscribed, very high signal intensity mass (arrowheads) in the left parotid gland (P). Other images (not shown) confirmed the cystic nature of the lesion and a first branchial cleft cyst was found at surgery.
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.
Coronal T1-weighted image in an HIV-positive patient with bilateral parotid gland enlargement demonstrates multiple small cysts (arrowheads) in both parotid glands as well as adenoidal hypertrophy (A). Findings are consistent with multiple lymphoepithelial cysts.
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.
Contrast-enhanced CT scan of the neck in a patient with clinical acute parotitis demonstrates marked enlargement and irregular enhancement of the left parotid gland as compared to the right (P, parotid glands); there is also enlargement of the ipsilateral masseter muscle as compared to the contralateral masseter muscle (Ma, masseter muscles) due to inflammatory myositis. Infiltration of the overlying subcutaneous fat on the left is due to associated cellulitis (thin white arrows show subcutaneous fat of the fact); there is also stranding and infiltration of fat in the left parapharyngeal space as compared with the right (large white arrows indicate parapharyngeal spaces). No calculi were identified, and no abscess was present. The patient responded to intravenous antibiotic therapy.
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.
(A) Axial T1-weighted image in a young patient with a slowly enlarging right parotid mass shows a round, well-circumscribed lesion of intermediate signal intensity. Also indicated are the parotid glands (P), parapharyngeal space (PPS), internal jugular vein (IJV), internal carotid artery (C), lateral mass of C1 (C1), and the spinal cord (SC). (B) The mass is very bright on a fast spin-echo T2-weighted image with fat saturation. (C) Following gadolinium, the lesion enhances intensely and homogeneously. These are the typical imaging features of a pleomorphic adenoma and this diagnosis was confirmed pathologically.
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.
(A) Coronal Tl-weighted image in a 55-year-old woman with a mass (arrowheads) arising from the inferior aspect of the right parotid gland (P). The lesion is well circumscribed but quite heterogeneous, with internal areas of high signal intensity representing areas of hemorrhage or proteinaceous cysts. (B) The lesion is hyperintense on an axial fast spin-echo T2-weighted image with fat saturation, but also somewhat heterogeneous. The heterogeneity of the lesion and the areas of intrinsic T1 shortening are suggestive of a Warthin tumor, which was confirmed pathologically.
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).
Sagittal T1-weighted image in a patient with a mucoepidermoid carcinoma of the parotid. The mass has an irregular, spiculated margin. In addition, two parotid lymph nodes (black arrowheads) are seen, which are suggestive of local metastases.
Coronal postgadolinium T1-weighted image with fat saturation in an older man who had undergone a prior right parotidectomy for carcinoma ex pleomorphic adenoma demonstrates abnormal thickening and intense enhancement of the descending mastoid segment of the right facial nerve (arrowheads), consistent with the perineural spread of disease. The normal left parotid gland (P) is indicated. The patient had a progressive right facial palsy.
(A) Axial fast spin-echo T2-weighted image with fat saturation in a 60-year-old woman who has noted fullness in her right parotid region. Both parotid glands (P) are indicated, but the large right parotid mass is difficult to detect on this sequence. (B) Axial T1-weighted image demonstrates a large right parotid mass (arrows), which is easy to identify in contrast to the fatty glandular parenchyma. The low signal intensity on the T2-weighted image is suggestive of a malignant histology, and squamous cell carcinoma of the parotid gland was pathologically confirmed.
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.
The masticator space demonstrated on a coronal T1-weighted image. The space extends from the inferior edge of the mandible below (lower white arrowhead) to the superior attachment of the temporalis muscle above (upper white arrowhead); the zygoma (white arrow) represents the inferior margin of the suprazygomatic masticator space. The mandible (M) is indicated, as are the muscles of mastication: temporalis (T), masseter (Ma), medial pterygoid (MP), and lateral pterygoid (LP).
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.
Table 3–7. Lesions of the Masticator Space. ||Download (.pdf)
Table 3–7. Lesions of the Masticator Space.
|Hemangioma||Odontogenic infection:||Benign tumor of muscle or bone||Osteosarcoma|
|Venolymphatic malformation||Myositis||Nerve sheath tumor||Rhabdomyosarcoma|
|Masseteric hypertrophy||Non-Hodgkin lymphoma|
|Deep extension of mucosal squamous cell carcinoma|
Coronal T1-weighted image in a patient with a history of carcinoma involving the left masticator space and new lower facial numbness demonstrates marked enlargement of the foramen ovale on the left (arrowheads) and a masslike enlargement of V3 (m) due to the perineural spread of tumor. The normal right foramen ovale (*) is shown for comparison.
Axial fast spin-echo T2-weighted image (no fat saturation) in a patient with left-sided perineural spread of squamous cell carcinoma along V3 demonstrates marked asymmetry of the masseter (Ma) and medial pterygoid (MP) muscles, consistent with longstanding denervation atrophy on the left.
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).
(A) Axial T1-weighted image in a young man with a soft, slowly enlarging mass of the left buccal region demonstrates a well-circumscribed, slightly lobulated soft tissue intensity mass (black arrowheads). (B) Axial fast spin-echo T2-weighted image with fat saturation demonstrates the lesion to be very bright. Also demonstrated are the parotid ducts bilaterally (arrowheads), running over the surface of the masseter muscles toward the buccal space. (C) Coronal postgadolinium T1-weighted image with fat saturation through the most anterior aspect of the lesion demonstrates two low signal intensity, rounded masses (arrowheads) within what was otherwise a homogeneously and intensely enhancing lesion. These are consistent with phleboliths, confirming the diagnosis of a venous malformation.
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.
Axial contrast-enhanced CT scan of the neck in a patient with poor dentition, fever, pain, and facial swelling. Extensive abscess formation (A) is seen in the right masticator space. The normal left masticator space (M, mandible; MP, medial pterygoid; Ma, masseter; T, temporalis) is shown for comparison. The right pharyngeal wall is bowed medially, the parapharyngeal fat is obliterated, and the right parotid gland (P) is displaced posteriorly.
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.
(A) Axial T1-weighted image demonstrates a large, homogeneous mass, which is isointense to muscle and centered on the left masticator space. The mandible has been largely destroyed. (B) Postgadolinium, a coronal T1-weighted image with fat saturation demonstrates an area of irregular central nonenhancement, consistent with necrosis (N). The lesion abuts and erodes the floor of the left middle cranial fossa, but no gross intracranial extension is seen. A rhabdomyosarcoma was confirmed pathologically.
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.
Axial contrast-enhanced CT scan of the neck demonstrates the contents of the carotid space: the internal jugular vein (IJV), carotid artery (C), and cranial nerves (arrowhead). Note that the cranial nerves cannot be individually resolved and appear as a focal soft tissue density posterior and slightly lateral to the carotid artery. Also indicated are the bordering parotid (P) and parapharyngeal (PPS) spaces.
Table 3–8. Lesions of the Carotid Space. ||Download (.pdf)
Table 3–8. Lesions of the Carotid Space.
|Internal jugular vein thrombosis||Abscess||Paraganglioma||Neuroblastoma|
|Carotid artery thrombosis||Schwannoma||Non-Hodgkin lymphoma|
|Carotid artery aneurysm or pseudoaneurysm||Meningioma (from posterior fossa via the jugular foramen)||Direct extension of mucosal squamous cell carcinoma|
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.
(A) Sagittal T1-weighted image demonstrates a soft tissue mass arising at the level of the carotid bifurcation (B) and displacing the internal carotid artery posteriorly (arrowheads) and the external carotid artery anteriorly (arrow). (B) The mass is mildly bright on an axial fast spin-echo T2-weighted image with fat saturation and also demonstrates prominent vessels (arrowheads). The internal carotid artery (I) is displaced posteriorly and the external carotid artery (E) is displaced anteriorly. (C) Postgadolinium, the mass enhances intensely and homogeneously. These findings are classic for a carotid body tumor.
Axial T1-weighted image in a patient with bilateral glomus vagale tumors demonstrates round, well-circumscribed soft tissue masses displacing the internal carotid arteries (C) anteriorly. Prominent flow voids (arrowheads) are seen within both lesions.
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.
(A) Axial T1-weighted image demonstrates a well-circumscribed, homogeneous mass arising from the left carotid space, displacing the left internal carotid artery (C) anteriorly. No vessels are seen within the lesion. (B) Postgadolinium, the lesion enhances intensely. A few small areas of nonenhancement most likely represent small areas of cystic degeneration, as flow voids should have been seen on the T1-weighted image. The diagnosis of schwannoma was favored and was confirmed pathologically.
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.
Axial T1-weighted image in a patient with recurrent squamous cell carcinoma and new cranial neuropathy demonstrates abnormal soft tissue (black arrow) infiltrating the left carotid space between the internal carotid artery (C) and a thrombosed jugular vein (J). Normal fat between the vessels (arrowhead) is demonstrated on the contralateral side. Fine-needle aspiration confirmed squamous cell carcinoma in the carotid sheath.
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).
(A) A noncontrast CT scan of the neck in a 9-month-old girl with a neck mass and Horner syndrome demonstrates a relatively low-density lesion with some peripheral calcification (arrowheads). (B) Postcontrast, the mass is seen to be located medial to the internal carotid artery (C) in the right carotid space. The mass appears of low density and possibly cystic, but with some irregular thickness to its wall (black arrowheads). Fine-needle aspiration confirmed neuroblastoma.
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.
(A) Sagittal T1-weighted image demonstrates a hyperintense stripe of retropharyngeal fat in this slightly off-midline image. (B) Axial T1-weighted image demonstrates fat in the retropharyngeal space (RPS, arrowheads), which lies just anterior to the prevertebral muscles (longus colli [LC]).
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.
Normal, nonenlarged lateral retropharyngeal lymph nodes (arrowheads) are well seen on this axial fast spin-echo T2-weighted image with fat saturation.
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.
(A) Axial postgadolinium T1-weighted image with fat saturation in a young male with diabetes and extensive neck infection shows abnormal enhancement throughout the right masticator space, oral cavity, and parapharyngeal space. Focal areas of abscess formation are present (A), including in the retropharyngeal space (RPA). (B) Postgadolinium image through the upper mediastinum demonstrates the inferior extension of the process and a large mediastinal abscess (arrowheads).
(A) Axial contrast-enhanced CT scan of the neck in a young woman with 5 days of torticollis, odynophagia, a low-grade fever, and a slightly elevated white blood cell count demonstrates a fluid collection (F) in the retropharyngeal space. A few displaced contrastenhancing vessels are seen around the collection, but the peripheral enhancement that might be expected with a retropharyngeal abscess is not present. (B) Axial image at a more cephalad level demonstrates an irregular calcification anterior to the C2 vertebral body, consistent with calcific tendinitis of the longus colli muscle. The fluid collection seen in part A represents an associated retropharyngeal effusion.
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.
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.
Axial noncontrast CT scan of the neck in a patient with known cervical vertebral diskitis and osteomyelitis demonstrates a prevertebral fluid collection (F) displacing the retropharyngeal fat stripe (*) anteriorly. A prevertebral abscess was drained transcervically.
Axial contrast-enhanced CT scan of the neck demonstrates a large soft tissue mass (arrowheads) arising from and destroying the right lateral mass of the C1 vertebral body. The mass encases the right vertebral artery (small white arrow) and displaces the right prevertebral muscle and retropharyngeal fat anteriorly. The pathology demonstrated a plasmacytoma.
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).
Axial contrast-enhanced CT scan of the neck in a patient with lymphoma and multiple enlarged cervical lymph nodes (N) in the right neck. The right lingual tonsil (LT) is also somewhat prominent. The right jugular vein (arrowhead) is severely compressed. The normal fat-filled posterior cervical space (PCS) is outlined on the left.
Babbel RW, Harnsberger HR. The parapharyngeal space: the key to unlocking the suprahyoid neck. Semin Ultrasound CT MR
. (Reviews important anatomic relationships of this centrally located space.)
Chong VF, Fan YF. Pictorial review: radiology of the carotid space. Clin Radiol
. (Illustrates the imaging features of carotid space lesions.)
Davis WL, Harnsberger HR, Smoker WR, Watanabe AS. Retropharyngeal space: evaluation of normal anatomy and diseases with CT and MR imaging. Radiology
. (The review addresses the spectrum of lesions of the retropharyngeal space, the imaging features that mark a lesion as originating in this space, and whether there is a difference between the radiologic pattern of the suprahyoid and infrahyoid portions of the neck.)
Davis WL, Harnsberger HR. CT and MRI of the normal and diseased perivertebral space. Neuroradiology
. (A retrospective analysis of patients with lesions in the perivertebral space to identify the imaging features that mark a lesion as originating in the perivertebral space and to define the spectrum of pathology that occurs in this space.)
Moukheiber AK, Nicollas R, Roman S, Coze C, Triglia JM. Primary pediatric neuroblastic tumors of the neck. Int J Pediatr Otorhinolaryngol
. (Reviews clinical, imaging, and management issues related to pediatric cervical neuroblastic tumors.)
Mukherji SK, Castillo M. A simplified approach to the spaces of the suprahyoid neck. Radiol Clin North Am
. (This article presents a simplified approach to the various spaces of the suprahyoid neck and their anatomic components. Each space is discussed separately and is accompanied by a table that lists a differential diagnosis based primarily on the normal anatomic contents of the space.)
Pollei SR, Harnsberger HR. The radiologic evaluation of the parotid space. Semin Ultrasound CT MR
. (Reviews the radiologic anatomy and appearance of pathology of the parotid space.)
Tart RP, Kotzur IM, Mancuso AA, Glantz MS, Mukherji SK. CT and MR imaging of the buccal space and buccal space masses. Radiographics
. (Reviews the imaging anatomy and pathology of the buccal space.)
Tryhus MR, Smoker WR, Harnsberger HR. The normal and diseased masticator space. Semin Ultrasound CT MR
. (Reviews the radiologic anatomy and pathology of the masticator space.)
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.
Major spaces of the infrahyoid neck. Visceral space (VS; black arrows), retropharyngeal space (RPS), perivertebral space with prevertebral (PVS) and paraspinal (PSS) compartments, and posterior cervical space (PCS). Also indicated are two minor spaces, the fat-filled anterior cervical space (ACS) and the fat-filled superficial space (SS). (Modified and borrowed, with permission, from Smoker WR, Harnsberger HR. Differential diagnosis of head and neck lesions based on their space of origin. 2. The infrahyoid portion of the neck. AJR Am J Roentgenol 1991;157:155.)
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.
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.
Babbel RW, Smoker WR, Harnsberger HR. The visceral space: the unique infrahyoid space. Semin Ultrasound CT MR
. (Reviews the anatomy and pathology of the visceral space.)
Fruin ME, Smoker WR, Harnsberger HR. The carotid space of the infrahyoid neck. Semin Ultrasound CT MR
. (Reviews the anatomy and pathology of the infrahyoid carotid space.)
Shah RR, Lewin JS. Imaging of the infrahyoid neck. Neuroimaging Clin N Am
. (Reviews the complex anatomy and pathology of the infrahyoid neck with updated imaging techniques.)
Smoker WR. Normal anatomy of the infrahyoid neck: an overview. Semin Ultrasound CT MR
. (Reviews the complex anatomy and pathology of the infrahyoid neck.)
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).
Axial T1-weighted image in a 6-yearold girl with a submental vascular malformation demonstrates marked enlargement of the external carotid arteries (E) bilaterally, as well as multiple large flow voids (arrowheads) throughout the submandibular and sublingual spaces bilaterally. No associated soft tissue mass was seen and angiography (not shown) confirmed extensive arteriovenous malformation.
Baker LL, Dillon WP, Hieshima GB, Dowd CF, Frieden IJ. Hemangiomas and vascular malformations of the head and neck: MRI characterization. Am J Neuroradiol
. (Characterizes the MRI appearance of a common hemangioma of infancy as well as the low- and high-flow vascular malformations of the head and neck.)
Hartemink DA, Chiu YE, Drolet BA, Kerschner JE. PHACES syndrome: a review. Int J Pediatr Otorhinolaryngol
. (The spectrum of PHACES is reviewed.)
Mulliken JB, Glowacki J. Hemangiomas and vascular malformations in infants and children: a classification based on endothelial characteristics. Plast Reconstr Surg
. (A classic paper that clarifies the categorization of hemangiomas versus vascular malformations. This analysis provides a useful classification of vascular lesions of infancy and childhood and serves as a guide for the diagnosis, management, and further research.)
Vogelzang P, Harnsberger HR, Smoker WR. Multispatial and trans-spatial diseases of the extracranial head and neck. Semin Ultrasound CT MR
. (Reviews the imaging and differential diagnosis of multispatial processes of the head and neck.)
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).
Axial noncontrast CT scan of the neck demonstrates the intrinsic high density of the thyroid gland (T). Also shown are the esophagus (E), trachea (Tr), common carotid artery (C), internal jugular vein (J), and sternocleidomastoid muscle (SCM).
Axial T1-weighted image of the neck before (A) and after (B) the administration of gadolinium demonstrates homogeneous enhancement of the thyroid gland (T) following contrast administration.
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 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.
Axial contrast-enhanced CT scan of the neck in an elderly woman with a gradually enlarging neck mass demonstrates massive enlargement of a heterogeneously enhancing thyroid gland (arrowheads). There is maintenance of a smooth margin, however, and no evidence of any invasion of adjacent structures. No abnormal lymph nodes are identified. Adjacent structures are displaced and compressed by this large mass, notably, the trachea (Tr), esophagus (E), and carotid (C) and jugular (J) vessels. The surgical pathology confirmed diffuse goiter.
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.
Axial postgadolinium T1-weighted image with fat saturation demonstrates multiple lobulated enhancing masses (M) in the thyroid gland and multiple nodal masses (N) lateral to the carotid artery (C) and jugular vein (J). No invasion of the trachea (T) or esophagus (E) is seen. Fine-needle aspiration confirmed papillary carcinoma of the thyroid with multiple nodal metastases.
Axial T1-weighted image in a young woman who presented with an enlarged left level IIA lymph node (arrowheads) demonstrates that the node is intrinsically bright. Compare a normal intermediate signal intensity node on the right (N). Fine-needle aspiration confirmed metastatic papillary carcinoma of the thyroid. Also shown are the carotid artery (C) and jugular vein (J).
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.
Loevner LA. Imaging of the thyroid gland. Semin Ultrasound CT MR
. (The embryology, anatomy, and physiology of the thyroid are discussed; congenital, autoimmune, inflammatory, metabolic, and neoplastic diseases are reviewed; and the diagnostic utility of various radiologic imaging modalities is addressed.)
Loevner LA. Imaging of the parathyroid glands. Semin Ultrasound CT MR
. (The embryology, anatomy, and physiology of the parathyroid glands are reviewed. The diagnostic utility of radiologic imaging is discussed, particularly as it pertains to the evaluation of primary hyperparathyroidism.)
Yousem DM, Huang T, Loevner LA, Langlotz CP. Clinical and economic impact of incidental thyroid lesions found with CT and MR
. Am J Neuroradiol
. (Incidental thyroid lesions are frequently present and often overlooked on cross-sectional images of the neck in patients being examined for other reasons. The cost of pursuing a workup of these lesions and their high prevalence in the population raise questions regarding appropriate management strategies.)
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.
Table 3–9. Cystic Lesions of the Neck. ||Download (.pdf)
Table 3–9. Cystic Lesions of the Neck.
|Branchial cleft cyst||Ranula||Cystic schwannoma||Cystic nodal metastases||Saccular cyst|
|Thyroglossal duct cyst||Necrotic lymphadenopathy||Cystic thyroid carcinoma|
|Epidermoid or dermoid|
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.
Axial contrast-enhanced CT scan of the neck demonstrates a unilocular, well-circumscribed cystic mass (BCC) between the submandibular gland (SMG) and the sternocleidomastoid (SCM) muscle, anterolateral to the carotid space. This appearance is characteristic of a second branchial cleft cyst.
Axial contrast-enhanced CT scan of a 14-month-old girl with recurrent redness and swelling of her left neck, as well as a draining pit just above her left clavicle. A peripherally enhancing tubular structure (arrow) could be followed from the upper neck down to the level of the clavicle, representing a second branchial apparatus sinus tract. Note its location between the submandibular gland (SMG) and the sternocleidomastoid (SCM) muscle.
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.
Axial contrast-enhanced CT scan of a young man with right anterior neck swelling demonstrates a well-circumscribed cystic mass adjacent to the right thyroid lamina, embedded in the strap muscles, which are displaced around the periphery of the lesion (arrowheads). Surgical excision confirmed a thyroglossal duct cyst.
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.
(A) Axial fast spin-echo T2-weighted image with fat saturation demonstrates a lobulated lesion of the left face with evidence of prior internal hemorrhage and multiple fluid-fluid levels (arrowheads) in its multiple cystic spaces. This is a typical appearance for a lymphangioma. (B) Postgadolinium, there is linear enhancement of the fibrous septa bordering some of these cystic spaces, which is often present in lymphangiomas. Some ill-defined enhancement more posteriorly and laterally is likely related to inflammation as this patient had a prior infection of the lesion as well as prior hemorrhage into it.
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.
(A) Coronal T1-weighted image in a 55-year-old woman with a submental mass demonstrates a rounded, well-circumscribed mass located in the midline between the anterior bellies of the digastric muscles (D). The lesion is somewhat bright on the T1-weighted image, suggesting fatty, proteinaceous, or hemorrhagic content. (B) On a postgadolinium coronal T1-weighted image with fat saturation, the lesion is seen to decrease in signal intensity. Hemorrhagic or proteinaceous material would not be expected to lose signal on a fat saturation image, but fatty material does. This suggests the diagnosis of dermoid cyst, which was confirmed surgically.
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.
(A) Sagittal T1-weighted image of the neck in a 22-month-old boy with a gradually increasing neck mass demonstrates a well-circumscribed, bilobed mass that is slightly bright on the T1-weighted image and extends inferiorly into the superior mediastinum. (B) Axial fast spin-echo T2-weighted image with fat saturation shows that the mass is extremely bright and has a slightly irregular internal septation (black arrow). It displaces the trachea (Tr) and esophagus (E) to the right. The mild hyperintensity on T1-weighted image is likely due to elevated protein content of the cyst fluid. On a postgadolinium image (not shown) there was mild enhancement of the internal septation, but no other enhancement. A foregut cyst was diagnosed at surgery.
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.
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.
Cohen SR, Thompson JW, Brennan LP. Foregut cysts presenting as neck masses. A report on three children. Ann Otol Rhinol Laryngol
. (Three patients are presented in detail, and the histopathology and differential diagnosis are discussed. Surgical extirpation of the cyst should be curative.)
Davison MJ, Morton RP, McIvor NP. Plunging ranula: clinical observations. Head Neck
. (Reviews the etiology, clinical presentation, imaging, and surgical management of plunging ranulas.)
Glastonbury CM, Davidson HC, Haller JR, Harnsberger HR. The CT and MR imaging features of carcinoma arising in thyroglossal duct remnants. Am J Neuroradiol
. (The presence of a solid nodule or invasive features in association with a thyroglossal duct lesion visible on CT scans or MRI raises the question of thyroglossal duct carcinoma. Calcification is also associated with carcinoma.)
Koeller KK, Alamo L, Adair CF, Smirniotopoulos JG. Congenital cystic masses of the neck: radiologic-pathologic correlation. Radiographics
. (Reviews the clinical and radiologic features of cervical congenital cystic masses.)
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.
Table 3–10. Limited Differential Diagnosis for More Common Pediatric Neck Masses. ||Download (.pdf)
Table 3–10. Limited Differential Diagnosis for More Common Pediatric Neck Masses.
|Congenital/Developmental||Infectious/Inflammatory||Benign or Neoplasm-like||Malignant|
|Lymphatic malformation||Suppurative lymphadenopathy||Fibromatosis colli||Neuroblastoma|
|Branchial cleft cyst||Hemangioma||Lymphoma|
|Thyroglossal duct cyst|
|Epidermoid or dermoid|
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.
(A) Axial T1-weighted image in a 2-week-old boy with torticollis and a left neck mass (arrows) demonstrates prominent soft tissue in the expected location of the sternocleidomastoid muscle. The right sternocleidomastoid muscle (SCM) is shown for comparison. (B) On an axial fast spin-echo T2-weighted image with fat saturation, the normal muscle is dark, whereas the left-sided mass (arrows) has areas of mixed high and low signal. (C) Postgadolinium, an axial T1-weighted image with fat saturation demonstrates the diffuse enhancement of the mass, whose location and morphology paralleled that of the sternocleidomastoid muscle on every image. These imaging features are consistent with fibromatosis colli, though rhabdomyosarcoma must be considered in the differential diagnosis.
Jaber MR, Goldsmith AJ. Sternocleidomastoid tumor of infancy: two cases of an interesting entity. Int J Pediatr Otorhinolaryngol
. (Reviews the diagnostic modalities and treatment options for this entity.)
Koch BL. Imaging extracranial masses of the pediatric head and neck. Neuroimaging Clin N Am
. (A thorough review that emphasizes the imaging characteristics of lesions by location: the orbit, the sinonasal cavity, the nasopharynx, the face and jaw, and the neck.)