Exploración audiovestibular en el schwannoma intralaberíntico intravestibular

Abstract

Introduction and objective: Intralabyrinthine schwannoma (IS) or primary schwannoma of the inner ear is a very rare, benign tumor that originates in the perineural sheath of the Schwann cells of the intralabyrinthine branches of the vestibulocochlear nerve, located in the membranous labyrinth. The prevalence is unknown and the mean age at diagnosis is 49 years (14-89 years), with no sex predilection. Definitive diagnosis is performed by magnetic resonance imaging (MRI), without being able to find pathognomonic symptoms or signs that correlate the clinical evolution with the findings in the MRI. Method: We present the audio-vestibular examination of two patients diagnosed with intravestibular IS. Results: CASE 1: A 59-year-old woman with intravestibular IS of the left ear (LE). Fluctuating hearing loss in low tones and permanent decrease in high tones. Brainstem Auditory Evoked Potentials (BAEP) with symmetric III-V interval and similar wave V latencies of both ears. Distortion products (DP) present in RE and LE only up to 2 kHz. Cervical vestibular evoked myogenic potentials (cVEMPs) with symmetric amplitude, and bithermal test (in videonystagmographic study) with left vestibular areflexia. CASE 2: 55-year-old woman, in ENT follow-up since 2004 and intravestibular IS of RE. Three episodes of sudden sensorineural hearing loss (SSHL), with partial recovery of hearing (fluctuating) in 2004, 2011 and 2020, leaving sensorineural hearing loss with permanent loss of high tones and partial loss of low tones. Normal tympanogram. BAEP with symmetric I-V interval. DP present in LE and absent in RE (except 2 kHz). cVEMPs with symmetric amplitude. In the bithermic test there is a right vestibular paresis of 74% and decreased gain in the head impulse test (vHIT) in the horizontal semicircular canal, with grouped saccades. Discussion: Intracochlear is the most frequent IS, with those affecting the semicircular canals (SC) being rarer, as in the cases we present. The two patients we describe have an intravestibular IS, where the auditory clinic is the most remarkable. The normality of the BAEP would testify that there has been no tumor invasion of the internal auditory canal. Vestibular paresis/areflexia on the affected side shows damage to the structures dependent on the superior vestibular nerve, despite the few symptoms. Conclusions: Although audio-vestibular tests are not specific to intravestibular IS, the findings presented should alert us to the need to request a high-resolution MRI for its diagnosis.