Somatosensory evoked potential identification of sensorimotor cortex in removal of intracranial neoplasms.

OBJECTIVE: To assess the ease and reliability of routine use of somatosensory evoked potentials (SSEPs) for identification of sensorimotor cortex in brain tumour removal and to document its influence on the performance and outcome of surgery.

METHODS: SSEPs in response to contralateral median nerve stimulation were recorded from the cortical surface by means of a four lead electrode strip. Polarity reversal of short latency SSEP waves was used to identify the position of the central sulcus in 46 consecutive craniotomies for removal of metastases, gliomas, or meningiomas located in, near, or overlying sensorimotor cortex.

RESULTS: SSEPs were successfully recorded in 43/46 cases (94%) with demonstration of polarity reversal in 42/43 (98%). SSEP localization led to modification of 14/42 (33%) procedures, most frequently because of either displacement or involvement of sensorimotor cortex by tumour. Six patients (14%) developed new neurological deficits but none of these was attributable to incorrect identification of sensorimotor cortex.

CONCLUSIONS: SSEP polarity reversal is a simple, reliable, accurate, and inexpensive method of localizing sensorimotor cortex under general anaesthesia. Correct identification is possible when sensorimotor cortex is displaced or when surface anatomy is obscured by tumour. Routine use of this technique should be considered in all procedures for lesions located near the central sulcus.