Electrocochleographic Study in Cases of Posterior Cranial Fossa Tumor

Abstract

Electrocochleography was performed on six patients with posterior cranial Fossa tumors which consist of three cases of acoustic neurinoma of grade II-III, a case of glioblastoma multiforme originating from cerebello-superior pons, a case of astrocytoma of grade III originating from medulla oblongata-inferior pons, and a case of meningioma originating from Meckel's cavity. Recording was made with the use of the transtympanic needle technique. AP input-output functions with acoustic neurinoma were very similar to those obtained in patients with sensorineural hearing loss showing the phenomenon of recruitment. In AP responses recorded from the patients with cerebello-superior pontine tumor and Meckel's cavity tumor, a loss of the positive portion of the potentials (P1) was characteristic. This phenomenon may be due to the compression on the auditory nerve by the growing tumor. The polarity of SP in all cases showed negative deflection without abnormal increment. CM responeses recorded from the patients were the same as in a normal subject. In the cases presented, although the abnormal changes in input-output functions as well as the changes in the wave form patterns of AP responses revealed a lesion of the portions corresponding to the sensory and/or to the neural structure, the presence of a well-developed CM may be explained by the fact that the hair cells remain unaffected. Therefore, it is thought that simultaneous recording of CM and AP gives great promise as a means of differential diagnosis between neural and cochlear pathology.