EXPRESS: Lack of Association Between Inner Ear FLAIR Suppression on MRI and Laterality of Clinical Signs in Feline Idiopathic Vestibular Syndrome

Abstract

Objectives The underlying aetiology of feline idiopathic vestibular syndrome (IVS) remains unclear. In humans, specific magnetic resonance imaging (MRI) sequences are used to demonstrate differences in endolymph composition between unaffected and affected inner ears. A previous study in dogs with IVS reported that in 93% of cases, the clinically affected side exhibited a lower degree of fluid-attenuated inversion recovery (FLAIR) suppression, which may indicate altered endolymph composition, potentially due to increased protein concentration. The objective of this study was to determine whether similar changes can be observed in cats with IVS. Methods Medical records from 3 referral hospitals were reviewed. Cats were included if they had a diagnosis of IVS, clear lateralisation of clinical signs, and had undergone brain MRI. Regions of interest (ROI) were manually outlined to define the inner ear on T2-weighted (T2w) and FLAIR images. The FLAIR suppression ratio for each ear was assessed by calculating the average grey value across both imaging sequences. Any unilateral reduction in suppression was compared with the direction of clinical signs. ROI area size was also measured to evaluate potential swelling or collapse of inner ear structures. Results Twenty-five cats met the inclusion criteria. No correlation was found between the clinically affected side and the degree of FLAIR suppression. In 11 of 25 cats, the identified abnormal side did not correspond to the lateralisation of clinical signs, whereas in 14 of 25 cats it did. ROI area measurements likewise showed no consistent association with the clinically affected side. Conclusions and relevance In the present cohort, these findings indicate that cats with IVS did not show a consistent association between clinical lateralisation and MRI-detectable endolymph changes, supporting the possibility of a different underlying pathophysiology compared with dogs.