Labyrinthine Abnormalities on MRI in Untreated Otosclerosis: Prevalence and Clinical Relevance

To determine the prevalence and clinical relevance of labyrinthine abnormalities detected by delayed 3D FLAIR MRI in untreated otosclerosis with labyrinthine symptoms, and to evaluate correlations with clinical and audiometric data.

Retrospective observational study, single tertiary referral center.

Thirty-four patients (58 ears) with confirmed otosclerosis by high-resolution CT presenting with labyrinthine symptoms and no prior surgery underwent 3T labyrinthine MRI with a post-contrast delayed 3D FLAIR sequence. Two blinded neuroradiologists independently reviewed CT to confirm otosclerotic and MRI to assess endolymphatic space anomalies and blood-labyrinth barrier (BLB) disruption. Findings were correlated with clinical symptoms and bone-conduction thresholds.

Otosclerotic foci most frequently involved the pre-stapedial region (57/58, 98%). Morphological anomalies of the endolymph were rare, with one case of endolymphatic hydrops (1/58, 2%). In contrast, BLB disruption was identified in 34/58 ears (59%), predominantly in the basal cochlear turn (34/58, 59%) and peri-saccular region (32/58, 55%). BLB disruption was strongly associated with endosteal involvement (76%) and round window involvement (89%), and was universally present in obliterative round window involvement (100%). Its prevalence increased with hearing loss type (55% in conductive, 66% in mixed, and 100% in pure sensorineural hearing loss). However, no significant correlation was found between BLB intensity and bone-conduction thresholds.

Endolymphatic hydrops was rare in untreated otosclerosis with labyrinthine symptoms. Conversely, BLB disruption was frequent in this symptom-select population, spatially correlated with otosclerotic foci, reflecting underlying microvascular remodeling. While not directly predictive of hearing thresholds, BLB disruption may represent an imaging biomarker of disease activity.