THE UTILITY OF MOTOR-EVOKED POTENTIAL MONITORING DURING INTRAMEDULLARY SURGERY

Monitoring of spinal cord function during surgery of the spine is high ly desirable for detecting neurological iatrogenic injury before it be comes irreversible. The goal of balancing complete surgical excision o f an intramedullary spinal neoplasm against the risk of iatrogenic neu rologic deficit is nowhere more critical than in a patient with a beni gn tumor and little or no preoperative neurologic dysfunction. Unfortu nately, at the time of excision, there is generally little objective f eedback available to the surgeon to guide the aggressiveness of the ex cision. Subjective factors, such as the appearance of the interface be tween tumor and normal tissue and the amount of manipulation of intact spinal tissue, required during tumor excision can be indirectly suppl emented by knowledge of the natural history of the disease based on th e tissue type reported from frozen sections. Lacking immediate, quanti tative physiologic data during resection, however, the correctness of the surgeon's attempt to balance aggressive excision and iatrogenic ne urologic deficit remains untestable until the postoperative neurologic examination. We here report a case wherein the use of intraoperative monitoring of motor-evoked potentials (MEPs) afforded us immediate fee dback on the effect of our excision and had significant influence in g uiding the aggressiveness of tumor removal while somatosensory evoked potentials (SSEPs) remained unchanged.