Air-conducted and skull-tap cervical vestibular evoked myogenic potentials in determining nerve division involvement in vestibular schwannoma patients.

BACKGROUND: Air-conducted and skull-tap cervical vestibular evoked myogenic potentials (AC-cVEMP and Tap-cVEMP) have been shown to be very promising tools in clinical practice. They are noninvasive, easy to obtain and - importantly - they require little time and the cost of the instruments is low.

OBJECTIVES: The aim of this study was to evaluate the usefulness of the combined use of ACand Tap-cVEMPs as a diagnostic tool for advanced assessment of vestibular schwannoma in determining tumor origin, and to investigate whether the results are helpful for a surgeon as an additional source of information about the tumor before surgery.

MATERIAL AND METHODS: ACand Tap-cVEMPs were acquired (with EMG-based biofeedback) from the sternocleidomastoid muscles (SCM) of 30 vestibular schwannoma patients just before surgery. The results were compared to the surgical information about nerve bundle involvement in the tumor and the size of the tumor obtained from magnetic resonance imaging (MRI).

RESULTS: On the tumor side, abnormal corrected amplitude asymmetry ratios were detected in 73.33% of the patients, abnormalities in P1-latencies in 70% of the patients, and both in 90% of the patients. The cervical vestibular evoked myogenic potential (cVEMP) results indicated the affected nerve division to be the inferior in 23.33% of the patients, the superior in 20% of the patients, and both in 46.67% of the patients. No cVEMP abnormalities were found in 10% of cases. The combined results of both ACand Tap-cVEMP were significantly compatible with the surgical information about the tumor origin. The number of abnormalities was significantly correlated with the tumor size.

CONCLUSIONS: The information provided by the combined application of ACand Tap-cVEMPs might be useful for a surgeon in presurgical planning, providing more detailed information about the tumor and the affected nerve division in the internal auditory canal. It is not a diagnostic replacement for MRI in vestibular schwannoma patients; however, in our opinion, ACand Tap-cVEMPs may serve as additional sources of information about the tumor before the surgery.