Abstract
The significance of caloric testing in patients with acoustic neuroma or sudden deafness was studied in regard to changes due to aging, canal paresis, and clinical course. Caloric testing was performed in 17 patients (19 ears) with acoustic neuroma and 33 patients (33 ears) with sudden deafness. No effects of aging on the maximal slow-phase velocity or duration of nystagmus were recognized on caloric testing of normal ears. Patients with a maximal slow-phase velocity of at least 20 degress/second and of a duration of 100 seconds were regarded as normal. Unilateral canal paresis was diagnosed when the maximal show-phase velocity on the affected side was less than 50% of that on the normal side or when the duration on the affected side was less than 60% of that on the normal side. Among the parameters of caloric testing, the maximal slow-phase velocity was considered to be most suitable for assessing function of the semicircular canal. It is believed that acoustic neuromas larger than 20mm produce canal paresis whereas those smaller than 10mm produce various symptoms according to, for example, the origin of the tumor. Although there was no clear correlation between the size of an acoustic neuroma and hearing, all patients with neuromas smaller than 10mm had only a slight hearing loss. Cancal paresis was recognized in all patients with acoustic neuroma who suffered from dizziness. On the other hand, some patients had canal paresis but no dizziness. No obvious hearing loss or difference in the maximal slow-phase velocity and duration between the right and left sides was seen in the observation period of 3 to 31 months in 3 of 4 patients treated with a gamma knife. No canal paresis was recognized in any patients with sudden deafness but without dizziness, and no canal paresis was seen in half the patients with dizziness. Perhaps dizziness is a temporary and reversible symptom of a cochlear lesion of the vestibular system. The probability of recovery of hearing in cases of sudden deafness was recognized to be related to caloric nystagmus reactions and hearing types, but no clear relation to the presence or absence of dizziness was observed.
