Vestibular autorotation test asymmetry analysis of acoustic neuromas.

The vestibular autorotation test (VAT) measures the vestibulo-ocular reflex (VOR) response from 2 to 6 Hz, during 18 seconds of active head movements, while the patient attempts to fixate on a wall-mounted target. A new method of measuring eye velocity asymmetry from VAT data is presented, based on computer estimation of the 0th harmonics of discrete Fourier spectra over short segments of digital eye and head velocity records. Eye asymmetries greater than a 3% normal range are shown to be directionally correlated with the side of the lesions in patients with unilateral labyrinthectomies. Among patients with a diagnosis of acoustic neuroma, who were tested preoperatively with the VAT, nine of nine patients showed eye asymmetries greater than 3% toward the side of the neuroma. Those patients with acoustic neuromas who have sufficiently vigorous high-frequency head responses showed mean percentages of eye asymmetry that were linearly correlated with the size of the acoustic neuroma. These results suggest that VAT high-frequency asymmetry provides a useful method of diagnostic evaluation of the side and extent of unilateral peripheral lesions.