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Compound Muscle Action Potentials and Spontaneous Electromyography Can be Used to Identify and Protect the Femoral Nerve During Resection of Large Retroperitoneal Tumors

¹ Neurophysiological Monitoring Service, University of California San Francisco, 533 Parnassus Avenue, U-491, Box 0220, San Francisco, CA 94143-0112, USA
² Department of Surgery, Division of Surgical Oncology, University of California, San Francisco, CA 94143, USA

Correspondence: Address correspondence and reprint requests to: Lanjun Guo, MD, MSc; E-mail: lanjun.guo{at}ucsfmedctr.org

Background: Resection of large retroperitoneal neoplasms may injure the femoral nerve, thereby causing a permanent neurological deficit. We used electrical neurophysiological monitoring to identify, map, and preserve the femoral nerve during surgical resection to reduce the risk of neurological deficit.

Methods: Seven patients with retroperitoneal neoplasms underwent eight resections. Compound muscle action potentials (CMAPs) were recorded from needle electrodes placed in the iliacus, quadriceps, and sartorius muscles. Spontaneous electromyography (EMG) was contnuously monitored from the same muscle groups. A handheld monopolar stimulator was used to elicit evoked EMG responses to identify and map the course of the femoral nerve. A stimulating strength of 10 mA was used to map the nerve. The stimulation threshold was tested after neoplasm resection to predict postoperative femoral nerve function.

Results: Electrical stimulation with CMAP recording and a stimulating strength of 10 mA successfully localized the femoral nerve in six cases. Monitoring with a stimulating threshold between 0.6 and 1.6 mA predicted postoperative femoral nerve preservation after tumor resection in four of the six cases.

Conclusion: Neurophysiological monitoring using CMAP and spontaneous EMG can protect the femoral nerve during resection of large retroperitoneal neoplasms.

Key Words: Retroperitoneal sarcoma • Intraoperative neurophysiological monitoring • Femoral nerve • Electrical stimulation • Electromyography