Vestibulo-Ocular Reflex Results in Patients with Intralabyrinthine Schwannomas: Case Series with a Literature Review.

Background and Clinical Significance: Intralabyrinthine schwannoma (ILS) is a rare benign tumor of the inner ear, often presenting with nonspecific symptoms such as hearing loss, tinnitus and vertigo. Vestibular function in ILS patients remains underexplored. This study aims to evaluate vestibulo-ocular reflex (VOR) function and inner ear magnetic resonance imaging (MRI) signal changes in ILS, and to provide insights into potential mechanisms underlying vestibular dysfunction. Case Presentation: We report four cases of MRI confirmed ILS, including two intravestibular and two intravestibulocochlear schwannomas. All patients exhibited unilateral canal paresis on caloric testing, and two of three showed abnormal video head impulse test (vHIT) with decreased VOR gain and corrective saccades. Decreased signal intensity was observed in the semicircular canals in three cases, in the vestibule in one case, and in the cochlea in one case. A systematic literature review including 10 studies (n = 171) showed a 73.3% rate of abnormal caloric responses. Five studies conducted vHIT, reporting reduced mean VOR gain and corrective saccades, though quantitative analysis was limited. Cervical and ocular vestibular evoked myogenic potential abnormalities were found in 68.4% and 65.7% of reported cases, respectively. Conclusions: Impaired VOR function in patients with ILS may result not only from anatomical disruption but also from underlying biochemical or metabolic alterations within the inner ear.