conductive hearing loss

**Definition/Pathophysiology:** Sound is not efficiently conducted from the outer/middle ear to the cochlea. Problems lie in the external auditory canal, tympanic membrane (TM), middle ear space, or ossicular chain (malleus, incus, stapes). The cochlea and CN VIII are intact, so bone conduction (which bypasses the middle ear) is preserved. Maximum loss is about 60 dB, since bone conduction still works.

**Tuning fork tests:** - Rinne: Normal is AC > BC (positive). In CHL, BC > AC (negative) in the affected ear. - Weber: Lateralizes TO the affected (worse) ear. Mechanism: there is no masking by environmental noise in the affected ear, and the occluded ear amplifies bone-conducted sound. - Compare sensorineural hearing loss (SNHL): Rinne is positive (AC > BC, both reduced), and Weber lateralizes AWAY from the affected ear (toward the good ear). - Audiometry: CHL shows an air-bone gap (≥10 dB), with normal bone conduction thresholds. Tympanometry helps localize the problem.

**Causes by location:** - External ear: cerumen impaction (most common), foreign body, otitis externa with canal edema, exostoses ("surfer's ear"), atresia/stenosis, tumors. - TM: perforation (trauma, barotrauma, infection), tympanosclerosis. - Middle ear: - Otitis media with effusion or acute otitis media (flat tympanogram, Type B). This is the most common cause in children, often from eustachian tube dysfunction. - Otosclerosis: abnormal bone remodeling with stapes footplate fixation at the oval window. It is often autosomal dominant, typically presents in young to middle-aged adults (women, with worsening in pregnancy), and gives bilateral progressive CHL. Tympanometry is Type As (low compliance), the TM looks normal, and Schwartze sign (reddish promontory) may be seen. Carhart notch: dip in bone conduction at 2 kHz. Treatment is stapedectomy/stapedotomy or hearing aids. - Cholesteatoma: keratinizing squamous epithelium in the middle ear. It causes painless, foul-smelling otorrhea, CHL, and can erode ossicles and the facial nerve canal. Treatment is surgical. - Ossicular discontinuity (trauma), glomus tympanicum/jugulare tumor (pulsatile tinnitus, retrotympanic red mass). - Congenital: Treacher Collins and first/second arch syndromes (ossicular malformations). - Osteogenesis imperfecta: blue sclerae with CHL from ossicle fragility.

**Tympanometry patterns:** Type A = normal. Type As = stiff (otosclerosis). Type Ad = hypermobile (ossicular discontinuity). Type B = flat (effusion, or perforation with large canal volume). Type C = negative middle ear pressure (eustachian tube dysfunction).

**Management:** Treat the underlying cause: cerumen removal, antibiotics/tympanostomy tubes for recurrent or persistent effusion, tympanoplasty for perforation, ossiculoplasty, stapedectomy for otosclerosis, and mastoidectomy for cholesteatoma. Hearing aids or bone-anchored hearing aids are options when surgery is not an option.

**Board pearls:** Unilateral CHL in an adult with serous otitis media should prompt evaluation of the nasopharynx for a mass (nasopharyngeal carcinoma, especially in Asian patients or with EBV association) causing eustachian tube obstruction. Loud-noise exposure and aminoglycosides/loop diuretics/cisplatin cause SNHL, not CHL. Presbycusis (high-frequency, bilateral) is SNHL. Paracusis of Willis (hearing better in noisy environments) is classic for otosclerosis.