Cochlear nerve conduction block: an explanation for spontaneous hearing return after acoustic tumor surgery.

In the presence of an intact cochlear nerve, hearing loss has been attributed to either transection or spasm of the internal auditory artery or direct mechanical trauma to the cochlear nerve during tumor manipulation. Such events have been correlated with changes in intraoperative auditory evoked potentials. The possibility of a reversible conduction block in the cochlear nerve, however, has not been investigated. Review of four cases of delayed spontaneous recovery of hearing several months after acoustic tumor resection suggests that a conduction block phenomenon may exist. By comparing recent pertinent animal data with clinical intraoperative electrophysiologic data obtained during posterior fossa surgery in human subjects, we attempt to elucidate further the pathophysiology and intraoperative predisposing factors to cochlear nerve injury during hearing preservation procedures.