Eighth Nerve Tumors: Their Roentgen Manifestations

Eighth nerve tumors account for about 6 per cent of all intracranial neoplasms (12, 18). As they are particularly suited to surgical removal, their early recognition is essential. The present study was undertaken to see how often we, as radiologists, help in their diagnosis. The data upon which this report is based were taken from the records of the Neurosurgical Services of the Hospital of the University of Pennsylvania, the Graduate Hospital of the University of Pennsylvania, and the Temple University Hospital, made available to us through the kindness of the neurosurgeons of these hospitals, Dr. Francis C. Grant, Dr. Robert A. Groff, and Dr. Michael Scott. Records of 129 patients with proved 8th nerve tumors were reviewed. Of these, 83 were operated upon at the Hospital of the University of Pennsylvania, 29 at the Graduate Hospital of the University of Pennsylvania, and 17 at the Temple University Hospital. In 122 cases the verbal descriptions of the roentgen findings were considered satisfactory for analysis, and in 70 we personally reviewed and studied the roentgenograms. The purposes of the present communication are, first, to review the literature concerning the anatomy, pathology, and clinical findings in 8th nerve tumors, and second, to record their roentgen manifestations. Anatomy The 8th nerve enters the brain at the inferior border of the pons. It contains two groups of fibers , those supplying the cochlea, concerned with hearing, and those which supply the semicircular canals, the utricle, and saccule, which are concerned with posture and equilibrium. These portions of the acoustic nerve are known, respectively, as the cochlear nerve and the vestibular nerve (12, 11, 3). As the nerve passes from the internal auditory canal to the brain stem, it courses through a space below the tentorium in the posterior fossa known as the “cerebellopontile angle.” Called more specifically the “subtentorial angle” by Stibbe (34), it is bounded above and laterally by the sloping rigid tentorium, below and laterally by the sloping posterior surface of the petrosa, and above and medially by the inferior surface of the cerebellum and the side of the pons. This portion of the subarachnoid space measures about 1/2 inch in width and 1 inch in depth. It contains cerebrospinal fluid in a fine network of trabeculae which stretch from the arachnoid on the bone to the pia mater on the cerebellum and pons. Crossing this space are the 5th, 7th, and 8th nerves, the nervus intermedius, and the anterior inferior cerebellar artery and vein. The cochlear division of the acoustic nerve lies slightly behind the vestibular branch, but the entire 8th nerve, 7th nerve, and nervus intermedius course as a group through the angle into the internal auditory canal (34). One need but think of the many structures crowded together into the subtentorial angle to realize why 8th nerve tumors so often affect neighboring cranial nerves.