Rudimentary otocyst, or otocyst deformity, is a type of congenital inner ear malformation characterized by a small otic capsule remnant not connected to the brainstem.
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Clinical presentation
These ears show profound sensorineural hearing loss 1.
Pathology
Rudimentary otocyst represents an anomaly that is more differentiated than complete labyrinthine aplasia but less so than common cavity. The causative insult likely occurs early in the 3rd–4th week of development, when the inner ear is in the form of the otic vesicle 2.
Classification
Rudimentary otocyst was introduced in Sennaroglu's classification of inner ear malformations 1.
Radiographic features
CT
There is a round or ovoid cystic space that is at most a few millimeters in diameter in the place of the inner ear 1. The internal auditory canal is absent 1. Rudimentary semicircular canals may be present 1. The bony carotid canal is absent 3.
Treatment and prognosis
Rudimentary otocyst is a definite indication for auditory brainstem implantation rather than cochlear implantation 1.
Differential diagnosis
- complete labyrinthine aplasia features no cystic space in the inner ear
- common cavity is also a round cystic space but is associated with an internal auditory canal that opens into the center