Cochlear aplasia, or complete absence of the cochlea is a rare anomaly which accounts for only 3% of cochlear malformations.
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Radiographic features
- complete absence of the cochlea. Dense otic bone is seen at the anatomical site of the cochlea 2
- cochlear nerve canal and cochlear nerve are absent
- cochlear promontory is hypoplastic and flattened
- the vestibule and semicircular canals are often malformed, stunted, dilated but may be normal
- vestibular aqueduct is normal
- internal auditory canal usually hypoplastic
- facial nerve canal usually anomalous showing obtuse angle anterior genu
- middle ear is usually normal sized with normal ossicles
- oval window usually normal but may be atreticÂ
Differential diagnosis
-
labyrinthitis ossificans
- normal-sized bone is seen anterior to the IAC
- the bulge of the cochlear promontory produced by the basal turn of the cochlea is present
- common cavity deformity
- cystic cochleovestibular anomaly
- labyrinthine aplasia