ABR waveforms were analyzed in 63 subjects with tumors of the pontocerebellar angle. The tumors were diagnosed by CT scan and the diagnoses were surgically confirmed. According to the latency changing and amplitude size, the ABR waveforms were classified into seven types (0, A, B, C, D, E and F). All tumors were divided into groups (depending on size), and into subgroups (depending on type). Types 0–E were found in tumors of all sizes. Type C of the brain stem response (BSR) waveform (only 1 deflexion present) was revealed in 75 % of tumors greater than 20 mm. In this case tumor size may be predicted with the significance level of 5 %. Type F of the BSR waveform was found in tumors other than neuromas. Contralateral BSR is affected by tumors greater than 20 mm, and from the statistic point of view significantly more often by neuroma (significance level 5 %) than by other tumors.

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