gms | German Medical Science

Objective: During surgery for intra- or periorbital tumors, we intraoperatively recorded evoked compound muscle action potentials (ECMAPs) from the extraocular and intraocular muscles. Intraoperative cranial computer tomography (iCCT) allows on the one hand resection control during surgery and on the other hand location control of intraocular needles. We analyzed how this type of intraoperative electrophysiological monitoring control and resection control could minimize postoperative cranial nerve palsy.

Method: We analyzed patients with sphenoorbital and orbital tumors for safe and complete resection from 01/2012 to 10/2013. The ECMAPs were recorded through a surface electrode applied to the extraocular muscle and/or needle electrodes inserted into the superior intraorbital space. The surgeon repeated electrical stimulation whenever tissue of unknown origin was encountered intraoperatively. For further neuromonitoring control and resection control, we performed iCCT.

Results: We analyzed 15 patients with sphenoorbital or orbital tumors: 11 meningiomas, 3 fibrous dysplasias, 1 metastasis. Using these monitoring techniques, the response-free areas were resected and the areas from which ECMAP responses were recorded were avoided. For 15 patients, ECMAPs were successfully recorded from the intraocular muscles. 5 patients were simultanously recorded by extraocular surface muscle monitoring. 10 patients did not exhibit any postoperative deterioration of oculomotor nerve function. 3 patients exhibited deterioration of oculomotor nerve function immediately after surgery, which resolved within 3 monthes. 2 patients had a permanent functional deficit, but were already impaired before surgery. Better ECMAPs could be recorded by needle recording than by surface recording location controlled by iCCT. In 12 patients tumor were completely resected and in 3 patients small residual tumor was revealed by iCCT because of deteriorated neuromonitoring during resection.

Conclusions: ECMAP recordings from the intraocular muscles precisely indicated the locations of cranial nerves better than surface electrodes. These monitoring techniques are valuable in guiding surgeons to avoid inadvertent harm to the oculomotor, trochlear and abducens nerve during intra- or periorbital surgery, particularly when the neuroanatomic features are distorted by the presence of tumor. The iCCT enables tumor resection control and neuromonitoring control for intraorbital neuromonitoring.