Use of intraoperative neuromonitoring to prevent orbital complications in ethmoid sinus surgery

Orbital injury is one of the most serious complications in sinus surgery. Although these injuries are generally infrequent, there is a considerable increased risk for orbital complications during procedures in which anatomic landmarks are distorted because of the severity of disease or prior surgery. Currently there are no methods to detect early defects in the lamina papyracea or to prevent continued resection until orbital fat or periorbita is seen. Thirteen New Zealand white rabbits were studied by use of a nerve monitor to identify the periorbita and orbital fat in surgically created lamina defects. Evoked potentials were measured at the medial orbit when the lamina papyracea, periorbita, and orbital fat were stimulated at current intensities ranging from 0.25 to 1.00 mA. Stimulation of the lamina at 0.8 and 1.0 mA resulted in response amplitudes that were significantly lower compared with those of periorbita stimulation (means at 1 mA, 38.26 microV vs. 117.85 microV; p < 0.01). Stimulation of the orbital fat also resulted in higher potentials (mean, 59.47 microV) than those of the lamina papyracea (mean, 38.26 microV) but did not reach statistical significance. The statistically significant difference in response amplitudes between the lamina papyracea and the periorbita indicate that intraoperative monitoring may be useful in identifying early lamina defects, which could in turn reduce the risk of orbital injury during sinus surgery.