In a patient with auditory complaints, the goals in the evaluation are to determine: (1) the nature of the hearing impairment (conductive or sensorineural); (2) the severity of the impairment (mild, moderate, severe, profound); (3) the anatomy of the impairment (external ear, middle ear, inner ear, or central auditory pathway pathology); and (4) the etiology.
Initially, the history and the physical examination are critical in identifying the underlying pathology leading to the auditory deficit. The history should elicit hearing loss characteristics, including the duration of deafness, the nature of the onset (sudden or insidious), the rate of progression (rapid or slow), and the involvement of the ear (unilateral or bilateral). In addition, the presence or absence of the following conditions should also be ascertained: tinnitus, vertigo, imbalance, aural fullness, hyperacusis, otorrhea, headache, facial nerve dysfunction, and head and neck paresthesia. Information regarding head trauma, ototoxic exposure, occupational or recreational noise exposure, and a family history of hearing impairment may also be critical in the differential diagnosis.
A sudden onset of unilateral hearing loss, with or without tinnitus, may represent an inner ear viral infection or a vascular accident. Patients with unilateral hearing loss (sensory or conductive) usually complain of reduced hearing, poor sound localization, and difficulty hearing clearly with background noise.
Gradual progression in a hearing deficit is common with otosclerosis, noise-induced hearing loss, vestibular schwannoma, or Meniere disease. People with small vestibular schwannomas typically present with any or all of the following conditions: asymmetric hearing impairment, tinnitus, and imbalance (although rarely vertigo). Cranial neuropathy, especially of the trigeminal or facial nerve, may accompany larger tumors. In addition to hearing loss, Meniere disease or endolymphatic hydrops may be associated with episodic vertigo, tinnitus, and aural fullness. Hearing loss with otorrhea is most likely due to chronic otitis media or cholesteatoma.
In families with multiple affected members across multiple generations, the family history may be crucial in delineating the genetic basis of hearing impairment. The history may also help identify environmental risk factors that lead to hearing impairment within a family. Sensitivity to aminoglycoside maternally transmitted through a mitochondrial mutation can be discerned through a careful family history. Susceptibility to noise-induced hearing loss or age-related hearing loss (presbycusis) may also be genetically determined.
The physical examination should evaluate the auricle, external ear canal, and tympanic membrane. In examining the eardrum, the topography of the tympanic membrane is more critical than the presence or absence of the often-cited light reflex. The pars tensa (the lower two thirds of the eardrum) and the pars flaccida (the short process of the malleus) should be examined for retraction pockets that may be evidence of chronic eustachian tube dysfunction or cholesteatomas. Insufflation in the ear canal is necessary to assess tympanic membrane mobility and compliance.
Examination of Other Structures
A careful inspection of the nose, nasopharynx, and upper respiratory tract is indicated. Unilateral serous effusion in the adult should prompt a fiberoptic examination of the nasopharynx to exclude neoplasms. Cranial nerves should be carefully evaluated with special attention to trigeminal and facial nerve function as the dysfunction of these two nerves is most commonly associated with tumors involving a cerebellopontine angle.
Evaluation with a Tuning Fork
Evaluating hearing with a tuning fork can be a useful clinical screening tool to differentiate between conductive and sensorineural hearing loss. By comparing the threshold of hearing by air conduction with that elicited by bone conduction with a 256- or 512-Hz tuning fork, one can infer the site of the lesion responsible for hearing loss. The Rinne and Weber tuning fork tests are used widely both to differentiate conductive from sensorineural hearing losses and to confirm the audiologic evaluation results.
The Rinne tuning fork test is sensitive in detecting conductive hearing losses. A Rinne test compares the ability to hear by air conduction with the ability to hear by bone conduction. The tines of a vibrating tuning fork are held near the opening of the external auditory canal, and then the stem is placed on the mastoid process; for direct contact, it may be placed on either teeth or dentures. The patient is asked to indicate whether the tone is louder by air conduction or bone conduction. Normally and in the presence of sensorineural hearing loss, a tone is heard louder by air conduction than by bone conduction. However, with a 30-dB or greater conductive hearing loss, the bone-conduction stimulus is perceived as louder than the air-conduction stimulus.
The Weber tuning fork test may be performed with a 256- or 512-Hz fork. The stem of a vibrating tuning fork is placed on the head in the midline, and the patient is asked whether the tone is heard in both ears or in one ear better than in the other. With a unilateral conductive hearing loss, the tone is perceived in the affected ear. With a unilateral sensorineural hearing loss, the tone is perceived in the unaffected ear. As a general rule, a 5-dB difference in hearing between the two ears is required for lateralization.
The combined information from the Weber and Rinne tests permits a tentative conclusion as to whether a conductive or sensorineural hearing loss is present. However, these tests are associated with significant false-positive and -negative responses and therefore should be used only as screening tools and not as a definitive evaluation of auditory function.
The minimum audiologic assessment for hearing loss should include the following measurements: (1) pure-tone air-conduction and bone-conduction thresholds, (2) speech reception threshold, (3) discrimination score, (4) tympanometry, (5) acoustic reflexes, and (6) acoustic-reflex decay. This test battery provides a comprehensive screening evaluation of the whole auditory system. It allows the clinician to determine whether further differentiation of a sensory (cochlear) from a neural (retrocochlear) hearing loss is indicated. Refer to Chapter 45, Audiologic Testing, for additional details on audiologic assessment.
Appropriate radiologic studies may be needed to evaluate both the temporal bone and the auditory pathway. The radiologic evaluation of the ear is largely determined by what structures are being evaluated: the bony anatomy of the external, middle, and inner ear; or the auditory nerve and brain. Both computed tomography (CT) and magnetic resonance imaging (MRI) are capable of identifying inner ear malformations; they are equally able to determine the cochlear patency in the preoperative evaluation of patients for cochlear implantation.
Axial and coronal CT of the temporal bone with fine 0.6-mm cuts is ideal for determining the caliber of the external auditory canal, the integrity of the ossicular chain, and the presence or absence of middle ear or mastoid disease, and for detecting inner ear malformations. To reliably identify inner ear malformations, measurement of the cochlear height, lateral semicircular canal bony island width, and the vestibular aqueduct should be routinely performed on all temporal bone studies. CT scanning is also ideal for the detection of bone erosion often seen in the presence of chronic otitis media and cholesteatoma.
MRI is superior for imaging retrocochlear pathology such as vestibular schwannomas, meningiomas, other lesions of the cerebellopontine angle that may present with hearing loss, demyelinating lesions of the central nervous system, and brain tumors.
Most patients with conductive hearing losses should have axial and direct coronal CT scans of the temporal bones to evaluate the external and middle ear. Patients with unilateral or asymmetric sensorineural hearing losses should have an MRI of the head with gadolinium enhancement to exclude tumors of the cerebellopontine angle. In the presence of vestibular symptoms, patients may require electronystagmography and caloric testing.