Acoustic neurinomas.

Eight nerve tumors account for about 8 to 10% of all intracranial tumors, and for about 71 to 75% of all cerebello-pontine angle tumors. They occur particularly in the middle decades of life and are twice as frequent in females as in males. They originate from the distal neurolemmal portion of the nerve, in most instances, from the vestibular division, and represent a neoplasia of the cells of Schwann. Two prominent types of tissue "A" and "B" of Antoni can be distinguished histologically. Regressive changes are frequent and lend them a colorful appearance. Bilateral eighth nerve tumors occur in about 4%. These tumors reveal certain characteristic differences. The differential diagnosis must include: meningiomas, epidermoids and gliomas, as well as a number of other space-occupying lesions.