MRI Evaluation of Vestibular Endolymphatic Space in Patients with Isolated Cystic Lateral Semicircular Canal Malformation

Abstract

Isolated lateral semicircular canal dysplasia (LSCCD) is one of the most frequent malformations of the bony labyrinth. The aim of this study is to depict morphology and size of the vestibular endolymphatic space in patients with isolated LSCCD using a dedicated 3D high resolution MR sequence called 3D inversion recovery with REAL reconstruction (3D-REAL-IR). From January 2018 to February 2020, we reviewed 281 CT and 241 MR temporal bone studies, and 103 MR studies performed for the evaluation of endolymphatic hydrops (EH). Five patients with LSCCD were found, one of them with bilateral malformation. Three patients (four affected ears) underwent specific MR examination for the evaluation of EH, consisting of a heavily T2-weighed cisternography sequence (T2 SPACE) and a 3D inversion-recovery with REAL reconstruction. The endolymphatic volumetric ratio (ELR) was calculated as the total endolymphatic volume divided by the total lymph (vestibular) volume multiplied by 100. Hydrops MR imaging was available in four of the affected ears. ELR ranged from 22% to 81%. Both extremes were present in the same patient, corresponding to a patient with right unilateral Ménière’s syndrome but with bilateral LSCCD. A patient affected with hearing loss had an ELR of 33% and the last patient with unilateral probable Ménière’s syndrome showed an ELR of 42%. Endolymphatic hydrops imaging is feasible and can be performed on patients with inner ear malformations like LSCCD. The endolymphatic volumetric ratio could be a useful and reproducible tool in daily clinical practice.