Posterior Canal Fibrosis: A Case Series.

OBJECTIVE

To establish a case series where loss of magnetic resonance fluid signal intensity in the posterior semicircular canal (SCC) corresponded with a functional deficit on clinical and video head impulse testing, and most likely a result of canal fibrosis or obstruction.

PATIENTS: Three patients with an magnetic resonance imaging (MRI) showing loss of T2-weighted signal intensity in their posterior SCC corresponding to a vestibular weakness in that canal.

INTERVENTIONS: All patients underwent a comprehensive neuro-otologic examination. Vestibulo-ocular reflex was evaluated using clinical head impulse testing (cHIT) and quantified with video head impulse testing. MRI for all patients was obtained using clinical protocols for gadolinium-enhanced MRI of the internal auditory canal on 1.5 or 3 T scanners, which all included high-resolution, heavily T2-weighted imaging of the membranous labyrinth.

MAIN OUTCOME MEASURE: Correlation of MRI findings with vestibular weakness in the corresponding posterior SCC.

RESULTS

Subject 1 showed abnormal vHIT in the left lateral and left posterior SCCs. MRI showed loss of T2 signal intensity of the entire left posterior SCC as well as in the posterior limb of the superior SCC. Subject 2 showed isolated loss of function (cHIT) and low gain with catch-up saccade (vHIT) of the left posterior SCC. MRI showed loss of T2 signal intensity of the superior portion of the left posterior SCC, as well as in the posterior limb of the superior SCC. Subject 3 showed catch-up saccades of the left posterior SCC on cHIT and vHIT and loss of T2 signal intensity of the entire left posterior SCC and partial loss of bilateral lateral SCC on MRI.

CONCLUSIONS

In this case series, loss of posterior SCC function correlated with vestibular function testing and high-resolution, T2-weighted MRI findings, perhaps related to fibrosis of the posterior SCC.