Otology: Middle Ear Disease and Conductive Hearing Loss
Core concepts
Otology questions test the mechanics of sound transmission and the differential of conductive hearing loss. Know the tympanic membrane landmarks, ossicular chain, and the role of the Eustachian tube in middle ear pressure regulation. Understand otosclerosis (stapes fixation, progressive conductive loss, Carhart notch on audiometry, absent acoustic reflexes), chronic suppurative otitis media with cholesteatoma (epitympanic retraction, keratin debris, bone erosion, conductive loss with possible sensorineural component), and tympanic membrane perforation. Distinguish otitis media with effusion (flat tympanogram, type B) from normal (type A) and ossicular discontinuity or negative pressure (type C).
Traps in questions
- Carhart notch is a bone-conduction artifact, not true sensorineural loss.
- Cholesteatoma is a clinical/radiologic diagnosis; a "safe" perforation does not erode bone.
- Acoustic reflex absent with normal contralateral response suggests ossicular fixation or discontinuity.
- Tympanosclerosis produces conductive loss without active infection.
- Do not confuse otosclerosis (normal TM) with tympanosclerosis (visible plaques).
Worked rule of thumb
A patient with progressive conductive hearing loss, normal tympanic membranes, absent acoustic reflexes, and a Carhart notch most likely has otosclerosis. If the same patient has a perforation with keratin debris and bone erosion on CT, think cholesteatoma instead.