Intraoperative monitoring of median nerve somatosensory evoked potentials in cervical syringomyelia: analysis of 28 cases.

Intraoperative median nerve somatosensory evoked potentials (SEP) were monitored in 28 patients undergoing surgery for cervical or cervicothoracic syringomyelia. Analysis was focused on SEP components N13 (spinal cord), P14 (brain stem), and N20 (cortex). N13 was lacking in nearly 87% of the patients (due to a combined effect of syringomyelia and general anesthesia) and never recovered. P14 showed a significant (> 10%) intraoperative latency increase in two patients; this was irreversible in one patient who had a postoperative worsening of sensory function. N20 showed no relevant alterations. Pure motor deficits after surgery were not predicted by SEP monitoring. In conclusion, intraoperative P14 recording helped to identify harm to the dorsal columns and probably prevented the cord from irreversible damage in one case, whereas N13 recording did not contribute to the monitoring of spinal cord function during surgery for syringomyelia.