Monitoring auditory function during operations to remove acoustic tumors.

The use of auditory evoked potentials in the preservation of hearing is reviewed, and the feasibility of using brainstem auditory evoked potentials, electrocochleography, and compound action potentials directly recorded from the eighth nerve is discussed. The method of recording directly from the surface of the cochlear nucleus using an electrode placed in the lateral recess of the fourth ventricle is described, and the advantages of its use are demonstrated.