Audiovestibular findings and location of an acoustic neuroma.

Forty-one patients with unilateral acoustic neuroma (AN) were diagnosed by magnetic resonance imaging (MRI) between 1992 and 1997. All cases were analyzed with respect to tumor location and the results of audiometric examinations, auditory brainstem response (ABR) testing, and electronystagmography (ENG). Tumor location was determined by MRI and cases were divided into intracanalicular and extracanalicular sites. Intracanalicular tumors were significantly smaller than the extracanalicular ones The pure-tone hearing thresholds were better in ears with intracanalicular lesions than in those with extracanalicular ones. Respectively, speech reception thresholds were 33 dB and 45 dB, and speech discrimination scores 79% and 65%. ABR was abnormal in 98% of ANs, but was insufficient for determining tumor location. The ENG pursuit test was more frequently normal and the caloric side difference was smaller in ears with intracanalicular than extracanalicular AN. These findings show that the results of pure-tone and speech audiometry and ENG are better in ears with intracanalicular AN, while ABR results are similar regardless of tumor location.