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Below the Belt: Sensory Mapping and Monitoring in the Sacral-Pudendal Region

Eccher, Matthew A.

Journal of Clinical Neurophysiology: August 2014 - Volume 31 - Issue 4 - p 323–325
doi: 10.1097/WNP.0000000000000113
Invited Review

Summary: Originally described in 1982, scalp somatosensory evoked potential responses can be recorded after stimulation of multiple different pudendal nerve- and sacral root-supplied structures. The resulting P40 response is usually the highest amplitude at Cz. Responses are generally easy to resolve and therefore should be of equivalent ease to follow for neurophysiologic intraoperative monitoring versus lower limb peripheral nerve somatosensory evoked potentials (e.g., tibial or fibular [peroneal] nerves), but sizeable reports of pudendal somatosensory evoked potential monitoring are few. Direct orthodromic sensory nerve action potential recording from the cauda equina in response to single such sacral stimuli has been reported of utility for preserving roots that participate in urinary control during dorsal rhizotomy procedures for spasticity. Technical application of both techniques is quite straightforward. As in most areas of neurophysiologic intraoperative monitoring, there are no well-constructed historical control series informing use of these techniques and, certainly, no clinical trials. Given the socially devastating consequences of urinary and anal continence disturbances and a fairly high rate of functional postoperative disturbances when sacral roots are manipulated, this field begs more active clinical investigation.

Departments of Neurology and Neurosurgery, University Hospitals Case Medical Center, Cleveland, Ohio, U.S.A.

Address correspondence and reprint requests to Matthew A. Eccher, MD, MS, University Hospitals Case Medical Center, 11100 Euclid Avenue, LKS 6058, Cleveland, OH 44106, U.S.A.; e-mail:

© 2014 by the American Clinical Neurophysiology Society