FRAMELESS STEREOTAXIC GUIDANCE - AN INTRAOPERATIVE ADJUNCT IN THE TRANSORAL APPROACH FOR VENTRAL CERVICOMEDULLARY JUNCTION DECOMPRESSION

Methods. The application of a video-interactive frameless stereotactic guidance system for the treatment of ventral cervicomedullary junctio n compression is described in a patient with basilar invagination, odo ntoid dysgenesis, and a Chiari malformation who had irreducible imping ement on the ventral brainstem by a partially fused mass of bone made up of the malformed odontoid peg, the inferior clivus, and dorsally pr otruding osteophytes at the odontoid-clival junction. Results. This te chnology permitted instantaneous feedback of the surgeon's orientation in all planes, facilitating extensive removal of the dens and clival tip to achieve adequate ventral brainstem decompression. In view of th e distortion of the craniovertebral anatomy produced by the patient's anomalies, the ability to visualize three dimensionally the location o f the vertebral arteries also added an element of safety to the latera l bone removal. Similarly, the ability to localize the rostral limit o f the clivus that needed to be resected and the caudal extent of C2 th at needed to be removed to achieve an adequate decompression helped en sure that the extent of bone removal was appropriately tailored to the patient's anatomy. Conclusion. The authors believe this technique rep resents a significant advance over standard radiographic intraoperativ e localization techniques during transoral approaches to the ventral c ervicomedullary junction for patients in whom the odontoid is fixed in position in relation to the clivus. This is based on the speed with w hich localization can be obtained, the accuracy of the information pro vided, the ability to obtain localization in multiple planes simultane ously, and the lack of radiation exposure during the procedure.