Conductive hearding loss due to facial nerve aberrant canal and oval window dysplasia
Conductive hearing loss on the right side.
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An abnormal course of the facial nerve canal, overlying stapes and oval window:
- blue arrow: expected location of the facial nerve canal, tympanic portion, below the lateral semicircular canal, and superior and lateral to the oval window
- orange arrow: actual aberrant location
The 1st and 3rd portions of the facial nerve canal are normal.
No external ear anomalies, no ossicular chain ankylosis nor disruption, no inflammatory changes, no internal ear anomalies which could have caused conductive hearing loss are seen.
There is associated oval window and stapes dysplasia.
Facial nerve overlying the stapes footplate is a rare cause of congenital conductive hearing loss.
Stapes and oval window dysplasia are often associated and can be explained on an embryologic basis.
Possible differential diagnoses leading to misdiagnose of oval window dysplasia:
- Fenestral otosclerosis: different clinical history and a different evolutive course on imaging
- tympanosclerosis due to inflammatory changes: inflammatory changes are the main findings
- Wu CM, Ng SH, Liu TC. Facial nerve overlying stapes footplate as a cause of conductive hearing loss. (2008) Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology. 29 (8): 1204. doi:10.1097/MAO.0b013e3181656984 - Pubmed
- Barbara Zeifer, Paul Sabini, Jonathan Sonne. Congenital Absence of the Oval Window: Radiologic Diagnosis and Associated Anomalies. (2000) American Journal of Neuroradiology. 21 (2): 322. Pubmed