Bilateral Acoustic Tumors (4)

Abstract

Twenty-three Japanese patients with bilateral acoustic tumors were examined at Tokyo University Hospital during the period of 1960-1978. Clinical signs, symptoms, auditory and neurootological findings were reported in Practica Otologia Kyoto, Vol. 70 and 72.The data that follows were derived from a series of 11 patients with bilateral acoustic tumors. Investigations were made from the standpoints of vertical diameters of the internal auditory canal and their shape by petrous bone tomography. The data were compared with those obtained in 19 patients with unilateral acoustic tumors who were examined at Tokyo University Hospital during the period of 1974-1978.The maximum of the vertical diameter measured in each internal auditory canal ranged from 6 to 13mm with an average of 9.4mm in the bilateral acoustic tumors and 4 to 14mm with an average of 6.9mm in the unilateral acoustic tumors. There was a difference in the vertical diameter between the bilateral and unilateral acoustic tumors.The canals were separated in the following: straight when the variation in the vertical diameter was less than 1mm all along its length, oval when the medial and lateral ends of the canal were more than 1mm smaller from the middle diameter, and funnel-shaped when the medial diameter was greater than any other portion of the canal. In the bilateral acoustic tumors, 82 percent of the canals were oval, but in the unilateral acoustic tumors, 68 percent were funnel-shaped. This discrepancy may be accounted for by the different behavior between the bilateral and unilateral acoustic tumors. The tomograms of the internal auditory canal as well as the auditory and neurootological findings showed that the etiology of the bilateral acoustic tumors differs from that of the unilateral acoustic tumors.