Signs

Various forms of obstruction can occur at the level of the EAC (e.g., cerumen, foreign body, congenital canal atresia, inflammatory stenosis with acquired atresia, bony exostosis, canal cholesteatoma). Blockage of the EAC can cause up to a 40-dB hearing loss. The TM may be thickened from scarring or tympanosclerosis; it can be retracted from negative middle ear pressure and drape on the incus and stapes (e.g., myringoincudostapediopexy) or even onto the cochlear promontory. In addition, perforations of any size and middle ear effusion may interfere with the proper vibration of the ear drum and cause hearing loss. Interruption of the continuity or mobility of the ossicular chain can also cause CHL; ossicles may be eroded or missing.

Symptoms

Patients will report hearing loss, difficulty understanding speech in noisy environments, and occasionally tinnitus. Disorders of the EAC and TM (e.g., cholesteatoma, chronic otitis media) may also cause otorrhea and recurrent infections. Inciting events may be elicited, such as head trauma, recent upper respiratory tract infection, or flight. Causes of potential auditory (eustachian) tube dysfunction should be elicited, such as chronic sinusitis, allergic rhinitis, or cleft palate.

Differential Diagnosis

The differential diagnosis of CHL is broad and can involve disorders of the EAC, TM, middle ear, and ossicles. Disorders of the EAC include congenital atresia, cerumen, foreign body, exostosis, osteoma, and neoplasm. Disorders of the TM include scarring, tympanosclerosis, retraction, and perforation. Disorders of the middle ear can include adhesions and effusions and may stem from underlying auditory tube dysfunction. Disorders that can cause ossicular discontinuity or ossicular erosion are trauma, cholesteatoma, chronic otitis media, and neoplasm. Otosclerosis and malleus fixation can also impair the vibratory potential of the ossicular chain. Third window disorders such as semicircular canal dehiscence can also cause CHL.

Physical Exam

A full head and neck examination should be performed to elicit signs of underlying sinonasal disease, auditory tube dysfunction, or neoplasm. In an adult with persistent unilateral middle ear effusion, nasopharyngoscopy is performed to rule out nasopharyngeal mass causing auditory tube dysfunction. Binocular microscopic evaluation of the EAC and TM is extremely helpful in identifying pathology of CHL, which may otherwise be missed with a handheld otoscopy. Complete removal of cerumen aids in visualization. Pneumatic otoscopy can assist in determining TM mobility and should always be documented. The integrity of the manubrium of the malleus, long process of the incus, and stapes can also be seen on exam. In general, the Weber test with a 512-Hz tuning fork generally lateralizes to the ear with CHL. Depending on the degree of CHL, the Rinne test will demonstrate bone conduction greater than air conduction (“negative Rinne”).

Imaging

High-resolution computed tomography (CT) of the temporal bones is not necessary in all cases of CHL. CT scan is obtained when there is a chronically draining ear (e.g., chronic otitis media), evidence of cholesteatoma, or mass lesion of the EAC or middle ear or when the cause of CHL is unclear. CT can also be done for surgical planning (e.g., atresia repair). Otosclerotic foci can be demonstrated on CT, although imaging is not necessary in all cases.

Other Tests

Comprehensive audiometry with both air conduction and bone conduction testing should be performed to determine air–bone gap (ABG), which represents the amount of hearing loss attributed to the conductive mechanism. Tympanometry can be performed to determine the mobility of the drum, detecting perforations and middle ear effusions. Acoustic reflexes should be absent. If acoustic reflexes are present in a patient with a conductive hearing loss, superior semicircular canal dehiscence should be suspected. In this case, cervical vestibular evoked myogenic potential (cVEMP) testing can be helpful, as superior semicircular canal dehiscence syndrome patients typically demonstrate larger amplitudes and lower thresholds on cVEMP testing at 500 Hz.

Medical

Amplification and observation should be offered to patients as a treatment option. Amplification can include hearing aids and soft band (bone conducting hearing aid). Certain conditions may require surgical intervention prior to amplification (e.g., neoplasm, chronic otitis media, cholesteatoma).

Surgical

Surgical intervention can potentially improve hearing when there is a significant ABG. The surgery depends on the etiology of the CHL. Osseointegrated implants (see Chapter 3.5.5) are an alternative treatment for CHL that should be considered when surgery for the underlying disorder may carry high risk to sensorineural component of hearing or facial nerve (e.g., atresia).

Otosclerosis

Otosclerosis is a process in which the stapes loses mobility by excessive bony growth at the oval window. It typically causes a CHL with a distinctive dip in sensorineural levels at 2 kHz, known as Carhart notch. Patients may have tinnitus and progressive hearing loss in one or both ears. Otosclerosis has a bimodal age epidemiology; it usually presents in the early twenties or later in the fifties. Early otosclerosis can be managed with fluoride supplementation, but often the CHL will progress and patients will need to consider amplification or stapes surgery. Stapedectomy or stapedotomy involves removing the superstructure of the stapes, and entering into the inner ear, either by making a fenestration in the footplate (stapedotomy), or partially removing it (stapedectomy). A synthetic prosthesis is then placed into the oval window and attached to the incus to reestablish ossicular transmission of sound waves.

Ossicular Disease

Cholesteatoma, chronic ear infections, and trauma can all cause erosion or disruption of the ossicular chain. After appropriately treating the aforementioned causes, one may evaluate the remaining middle ear structures to determine the appropriate surgical repair. Once the current ossicular status (anatomic and functional integrity of each ossicle) is determined, the appropriate prosthesis can be selected. Prostheses exist for nearly every situation of ossicular disease. Common prostheses include a partial ossicular reconstruction prosthesis (replaces incus and malleus), incus struts (replace incus only), and a total ossicular reconstruction prosthesis (replaces all ossicles).

Signs and Symptoms

Patients typically notice difficulty in crowds or with background noise. They may report having to increase the volume of the television or radio to understand. Patients with high-frequency hearing loss may notice difficulty with understanding women or children′s voices. Many patients will not realize they have hearing loss until it has progressed significantly, as the hearing loss is usually very gradual. Often, tinnitus is associated with hearing loss and may be the presenting symptom. Other otologic symptoms, such as otorrhea, aural fullness, and vertigo, may also help identify the etiology of the hearing loss. Inciting events or risk factors for hearing may be present, such as head trauma, acoustic trauma, chronic loud noise exposure, family history of hearing loss, ototoxic drug use, prematurity, prenatal/postnatal infection, barotrauma, and autoimmune disease. A full review of systems concentrating on neurologic or rheumatologic symptoms may also imply the cause.

Differential Diagnosis for Symmetric SNHL

Hearing Loss Present at Birth

See Fig. 3.11 for a classification overview of hearing loss at birth. About 50% of cases are nonhereditary, from prematurity, sepsis, or TORCH infections (toxoplasmosis, rubella, cytomegalovirus, herpes simplex encephalitis, and otosyphilis). Of the 50% that are congenital hereditary cases, these may be syndromic (one-third of cases) or nonsyndromic (two-thirds of cases); see Table 3.10 . Of the nonsyndromic cases, ~80% are autosomal recessive.

Table 3.10 Hereditary syndromic hearing loss

Autosomal dominant	Autosomal recessive	Sex-linked
Treacher Collins	Usher	Alport
Goldenhar	Pendred
Waardenberg	Jervell-Lange-Nielsen
Branchio-oto-renal
Stickler

Hearing loss may be present at birth due to congenital defects in either the structure or the physiology of the inner ear. Cochlear malformations (e.g., Mondini malformation, common cavity, cochlear hypoplasia, cochlear aplasia) may be associated with various syndromes. Many cases of nonsyndromic congenital hearing loss have been attributed to chromosomal defects in the hair cell protein connexin 26 (Cx 26). Most congenital cases are now discovered early due to universal newborn screening programs. However, certain types, such as enlarged vestibular aqueduct syndrome, may not manifest until later in life. Auditory neuropathy can also cause unilateral or bilateral SNHL.

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