Persistent apogeotropic positional nystagmus of the lateral semicircular canal: clinical features and association with vestibular atelectasis on delayed 3D-FLAIR MRI.

Objective: Persistent apogeotropic positional nystagmus of the lateral semicircular canal, often classified as atypical lateral semicircular canal (SCC) BPPV (alBPPV), may occur without typical positional nystagmus or response to repositioning maneuvers, in the absence of neurological disease. We aimed to describe its clinical and radiological features and investigate the occurrence and clinical correlates of utricular/saccular atelectasis on delayed 3D-FLAIR MRI. Methods: Retrospective single-center study in a tertiary referral center. Patients underwent clinical, vestibular, auditory and electrophysiological assessment, including videonystagmography, video head impulse testing, and delayed 3D-FLAIR MRI. Results: Thirty-two patients (mean age 68 years, vertigo duration 6.8 years) were included. Apogeotropic nystagmus persisted in 75%, with 50% meeting cupulolithiasis criteria. Geotropic conversion occurred in 15, and 10% showed no nystagmus. Vestibular investigations did not reveal a consistent or homogeneous vestibular deficit pattern. No consistent auditory abnormality was identified. Vibration-induced and head-shaking nystagmus were present in 30 and 50%, respectively, with kinetic hyporeflexia in 30%. Among patients with interpretable delayed 3D-FLAIR MRI, vestibular atelectasis was identified in approximately 60%. No significant clinical, audiological, or vestibular differences were found between patients with and without atelectasis. Conclusion: Persistent apogeotropic positional nystagmus involving the lateral SCC in the absence of neurological signs may represent a heterogeneous vestibular disorder. Vestibular atelectasis was commonly observed among patients with interpretable delayed 3D-FLAIR MRI, although its clinical and pathophysiological significance remains uncertain.