Extensive Cochlear Otosclerosis: CT-MRI Correlation and the Diagnostic Value of Contrast Enhancement

Otosclerosis is a chronic disorder of the otic capsule. It is characterized by abnormal bone remodeling, which may extend beyond the fenestral region and involve the cochlea and other structures of the bony labyrinth. There are two main types of otosclerosis-retrofenestral (cochlear) and fenestral, the latter of which is much more common. We present multimodal imaging findings of extensive bilateral cochlear otosclerosis in a 59-year-old woman with chronic bilateral sensorineural hearing impairment, classified as grade 3 in the right ear and complete deafness in the left ear. High-resolution computed tomography (CT) demonstrated extensive grade 3 bilateral otospongiotic changes involving multiple cochlear turns and extending toward the vestibule, fissula ante fenestram, oval window, and the lateral semicircular canal. Pre-contrast T1-weighted magnetic resonance imaging (MRI) showed mild pericochlear hyperintensity, suggestive of otospongiotic bone remodeling. Matching post-contrast T1-weighted imaging findings corresponded with bilateral pericochlear and perilabyrinthine enhancement of the otic capsule, which is associated with findings compatible with an active otospongiotic bone remodeling. T2-weighted sequences showed preserved fluid signal within the labyrinth and no corresponding otic capsule abnormality. Although limited for directly depicting otospongiotic changes, the T2-weighted sequence was useful for assessing morphology and excluding alternative pathology. This case illustrates the complementary role of CT and MRI in demonstrating advanced active cochlear otosclerosis and draws attention to MRI findings that might otherwise be overlooked, especially those in post-contrast T1-weighted images.