Vestibular evoked myogenic potentials in neurofibromatosis 2

Neurofibromatosis 2 (NF2) is characterized by bilateral vestibular neurofibromas. Although the facial nerve, the cochlear nerve, and the superior division of the vestibular nerve can be evaluated before surgery, whether the inferior division of the vestibular nerve is affected remains undetermined without an operation. A total of 7 patients with NF2 (2 men and 5 women) underwent pure tone audiometry, caloric testing, vestibular evoked myogenic potential (VEMP) testing, and magnetic resonance imaging. Audiometry revealed mean hearing levels of less than 26 dB for 1 ear, 26 to 70 dB for 8 ears, 71 to 90 dB for 3 ears, and more than 90 dB for 2 ears. Caloric testing revealed an absent response in 71% of the 14 ears. Seven ears underwent VEMP testing, and only 1 ear (14%) displayed absent VEMPs. Magnetic resonance imaging depicted space-occupying lesions in all 14 auditory canals: small tumors in 3 ears, medium tumors in 7 ears, and large tumors in 4 ears. The tumor size of NF2 is related to the caloric response, but is unrelated to the mean hearing level or VEMPs. In conclusion, NF2 originates from the superior vestibular nerve more often than the inferior vestibular nerve. It more often infiltrates the cochlear nerve than the inferior vestibular nerve.