MRI and CT correlation in a case of cochlear otosclerosis in spongiotic phase

Clinical History

A 54-year-old patient with complaints of recent dizziness and progressive, bilateral sensorineural hearing loss with onset in adolescent age.

Imaging Findings

FLAIR images and T1 basal acquisition demonstrated the presence of isointense material around bony labyrinth on both sides, while DWI and T2 sequences were unremarkable.
After contrast media administration, a symmetric, bilateral, marginal enhancement of the region around the bony capsule of the labyrinth was proved. In association with clinical patient history, this finding was interpreted as a probable underlying otosclerosis. In order to confirm this hypothesis the patient underwent a CT scan of temporal bone which highlighted poorly calcified foci near the fissula ante fenestram associated with the presence of a lucent halo around the otic capsule, and confirmed the suspicion of cochlear otosclerosis in spongiotic phase.

Discussion

Otosclerosis is a disorder of unknown aetiopathogenesis affecting the bony capsule of the labyrinth, characterised by replacement of perilabyrinthine endochondral bone by highly vascular, spongy bone that may eventually calcify. The disease is usually bilateral and clinically manifests between 15 and 40 years of age with progressive conductive hearing loss, possible tinnitus and slight dizziness, and at last with a mixed-type hearing loss, or a sensorineural hearing loss.
The disease can affect the entire otic capsule but the most common localisation is represented by the anterosuperior board of oval window (fistula ante fenestram).
Fenestral otosclerosis starts just anterior to the oval window in the labyrinthine capsule and extends posteriorly where it can fix the stapedial footplate or cause invasion and thickening of the footplate, leading to a progressive ossicle rigidity and conductive hearing loss. CT examination can demonstrate widening of oval window, thickening of the stapes footplate, and small low-density lesions just anteriorly to the oval window.
Cochlear (or retrofenestral) otosclerosis is much less common, but is always associated with fenestral otosclerosis. Because of the damage to cochlear and nervous structures, these patients complain of a mixed-type hearing loss, or a sensorineural hearing loss.
CT temporal bone scans can demonstrate a rarefaction of bone which surrounds the cochlea, and sometimes around the vestibule, semicircular ducts, the internal auditory canal.
In the osteosclerotic phase, these radiolucent areas become sclerotic and calcified and can be indistinguishable from the normal otic capsule.
Because of its insensitivity to bone structure, MRI is not indicated in the radiologic evaluation of otosclerosis. Since MRI is frequently requested in patients with otologic disorders, coming to observation for tinnitus, dizziness and sensorineural hearing loss, pericochlear signal abnormalities on T1 and FLAIR images can be detected. These subtle incidental findings have to be carefully considered and accurately explored after contrast media administration in order to suspect spongiotic otosclerosis. CT confirmation is mandatory in order to formulate a correct diagnosis. In cases of fenestral otosclerosis, MRI is poorly sensitive, since it hardly demonstrates the enhancement of the region corresponding to stapedial footplate. MRI has been reported to be helpful in cases of pericochlear otosclerosis, demonstrating pericochlear and perilabyrinthine gadolinium enhancement in T1 weighted images, corresponding to the areas of bony abnormality seen on CT.
In case of fenestral type otosclerosis the therapy is represented by surgical stapedectomy and insertion of stapes-prosthesis, in case of cochlear type, the indication is pharmacological administration of sodium fluoride or cochlear implant.

Differential Diagnosis List

Final Diagnosis

Cochlear otosclerosis in spongiotic phase.

URL:	https://www.eurorad.org/case/8999
DOI:	10.1594/EURORAD/CASE.8999
ISSN:	1563-4086