Spatial navigation after surgical resection of an acoustic neuroma: pilot study

To characterize navigation errors made by patients with the absence of vestibular function on one side owing to surgical resection of an acoustic neuroma.

Seventeen young (18-38 years) and 9 older healthy individuals (67-83 years), as well as 5 patients 2 to 20 months following surgery (37-61 years), were studied. They sidestepped laterally with eyes closed toward memorized targets located 1.25 m to their right or left. They stopped when they judged that they were in front of the target. The position of head and body markers was recorded in three dimensions with a six-camera Vicon 512 system (Oxford Metrics Ltd., Oxford, UK). Navigation errors were (1) distance error, the distance between the end target and a perpendicular line drawn from the sternum to the plane of targets, and (2) deviation, the angle formed between the line joining the initial and end targets and the line joining the subject's shoulders.

Mean distance error was 20.9 +/- 22.0 degrees cm in patients, 29.6 +/- 30.3 cm in young healthy subjects, and -1.7 +/- 18.4 cm in older subjects (p < .01 compared with young subjects). Mean deviation was symmetric and 8 degrees and -3 degrees in healthy young and older subjects, respectively. In contrast, patients had a significantly larger deviation when navigating toward the side of their lesion than the intact side (13 degrees +/- 9 degrees versus 3 degrees +/- 9 degrees; p < .01).

Our results suggest that patients with vestibular deficits have impaired ability to control body rotations when walking sideways without vision toward the side of their vestibular lesion.