Histological evidence of intraoperative monitoring efficacy in selective dorsal rhizotomy

Abstract

It has been advocated that intraoperative electrophysiological monitoring is mandatory in selective dorsal rhizotomy (SDR). However, it is still uncertain whether the monitoring procedure effectively differentiates dysfunctional rootlets. We histologically analyzed sectioned rootlets in SDR, in order to confirm the efficacy of the monitoring. Seven children with cerebral palsy underwent SDR on the same protocol. The pieces of their sectioned nerve rootlets from L5 were examined histologically using an electron microscope. In each patient, two nerve rootlets, one with the most abnormal response to intraoperative electrical stimulation and the other with the least abnormal response, were examined. The electron microscope findings of the rootlets were compared with the electromyography (EMG) findings in the intraoperative stimulation. Among 14 examined nerve rootlets, definite abnormal EMG findings were seen in 5, which were 4 clonuses and one bilateral spread. All five rootlets with abnormal EMG findings showed axonal degenerations except one case, whose finding was dysmyelination. On the contrary, in the nine rootlets with normal EMG findings, eight rootlets had histologically minimum changes limited to the myelin sheath and one rootlet had dysmyelination without axonal degeneration. The nerve rootlets with abnormal EMG findings in the intraoperative stimulation have definite histological abnormalities. This indicates that intraoperative monitoring is a meaningful method for identifying the nerve rootlets to be sectioned. This finding should be reminded as a precaution when considering nonselective dorsal rhizotomy, especially, for children who are expected to stand up after the surgery.