Congenital ear anomalies and microtia — branching viva

Branch 1 — The grade, the canal and the hearing

The candidate should grade the right ear as Marx grade III microtia (a peanut-shaped vestige with a lobule but no recognisable architecture), the commonest grade, and identify the absent external canal as aural atresia. The expected finding is a conductive hearing loss on the right with a preserved sensorineural threshold, confirmed by ABR. ^[1]

Probe the embryology: the outer and middle ear develop from the first and second pharyngeal arches and the first pharyngeal cleft, so they fail together, while the inner ear develops separately from the otic placode of surface ectoderm and is usually spared — which is exactly why the loss is conductive, not sensorineural. Aural atresia blocks the conductive pathway to an intact cochlea, producing a maximal conductive loss of around fifty to sixty decibels. ^{[1] [11]}