Twenty Japanese patients with bilateral acoustic tumors were treated at Tokyo University Hospital during the period of 1960-1977. We have already reported the clinical signs, symptoms and the auditory findings. An analysis was made of the neurootological findings of 20 patients.
Among the forty ears of 20 patients, the caloric test results were as follows: no response in 29 ears, decreased response in 8, and normal response in 3 ears.
Only 3 of 16 patients revealed positional nystagmus. The presence of positional nystagmus in bilateral acoustic tumors was less frequent than unilateral acoustic tumors, as most patients with bilateral acoustic tumors had a bilaterally decreased caloric function.
Regarding spontaneous nystagmus in 18 patients, gaze directional nystagmus was noted in 11 cases, and no nystagmus in five cases.
The patients who showed no evidence of spontaneous nystagmus and good response of optokinetic nystagmus were considered to have small sized tumors. However, neuroradiological findings, particularly CT scan, showed relatively larger sized tumors in these patients.
We have already reported that there is less correlation between auditory findings and tumor size of bilateral acoustic tumors than unilateral acoustic tumors. Such behavior of bilateral acoustic tumors was also seen in the neurootological results.
Even in some patients with large sized bilateral acoustic tumors which were assumed to adhere to the brain stem, several patients showed no sign of brain stem dysfunction. Bilateral acoustic tumors have less influence on the surrounding tissues than do unilateral tumors. These results suggest that the etiology of bilateral acoustic tumors differs considerably from that of unilateral acoustic tumors.
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