Intraoperative Electrocochleography of Posterior Fossa Tumors Producing Meniere's Syndrome

Objectives: Intraoperative electrocochleography (ECochG) has provided insight regarding inner ear pathophysiology during neurotologic procedures. In this study, intraoperative ECochG findings are reported in patients who presented with episodic aural and vestibular symptoms during resection of posterior fossa neoplasms. Patients: Three patients with episodic vertigo who underwent resection of posterior fossa tumors. Intervention: Intraoperative ECochG was performed before and after tumor resection with the active electrode at the round window. Acoustic stimuli consisted of click and tone bursts presented in alternating polarity. Main Outcome Measure: ECochG responses including summation potential (SP), action potential (AP), and SP:AP ratio values to evaluate for endolymphatic hydrops. Results: All subjects presented with asymmetric sensorineural hearing loss (SNHL), episodic vertigo, and tinnitus. Subject 1 was a 63-year-old woman who underwent left translabyrinthine excision of an endolymphatic sac (ELS) tumor and demonstrated no measurable responses until fenestration of the lateral semicircular canal, suggesting severe hydrops relieved by labyrinthotomy. Subject 2 was a 44-year-old woman who underwent right ELS tumor resection and exhibited an elevated SP:AP ratio. Subject 3 was a 55-year-old woman who underwent right retrolabyrinthine resection of a meningioma and exhibited robust responses without hydrops. Conclusions: Endolymphatic hydrops secondary to mechanical obstruction by a posterior fossa neoplasm may be demonstrated using intraoperative ECochG. Immediate improvement of hydrops may not be demonstrated after tumor resection.