Elevated summating potential in a case of posterior fossa meningioma was normalized by tumor removal

Objective: A change in the summating potential (SP) obtained from a patient with posterior fossa meningioma associated with surgical removal of the tumor was reported and possible mechanisms underlying the change are discussed. Methods: This paper is a retrospective case review. A tertiary care referral center was the setting for the study. The authors present a 46-year-old female patient with posterior fossa meningioma, which was removed surgically. Pure tone audiometry and electrocochleography (ECoG) were performed before and after surgical removal of the tumor. Results: Pure tone audiogram showed normal hearing levels before surgery, and there were no apparent postoperative changes in hearing levels. ECoG showed a normal compound action potential (AP) level and an elevated SP/AP ratio (0.53) before surgery. After the tumor removal, the SP/AP ratio became 0.16, which was a normal level in our department. Conclusions: The increased SP/AP ratio was normalized after surgery. Possible mechanisms underlying the increase in SP/AP ratio are an inhibition of the olivocochlear bundle function and endolymphatic hydrops.