INTRAOPERATIVE MAGNETIC-RESONANCE-IMAGING WITH THE MAGNETOM OPEN SCANNER - CONCEPTS, NEUROSURGICAL INDICATIONS, AND PROCEDURES - A PRELIMINARY-REPORT

OBJECTIVE: Intraoperative magnetic resonance imaging (MRI) is now avai lable with the General Electric MRI system for dedicated intraoperativ e use. Alternatively, non-dedicated MRI systems require fewer specific adaptations of instrumentation and surgical techniques. In this repor t, clinical experiences with such a system are presented. METHODS: All patients were surgically treated in a ''twin operating theater,'' con sisting of a conventional operating theater with complete neuronavigat ion equipment (StealthStation and MKM), which allowed surgery with mag netically incompatible instruments, conventional instrumentation and o perating microscope, and a radiofrequency-shielded operating room desi gned for use with an intraoperative MRI scanner (Magnetom Open; Siemen s AG, Erlangen, Germany). The Magnetom Open is a 0.2-T MRI scanner wit h a resistive magnet and specific adaptations that are necessary to in tegrate the scanner into the surgical environment. The operating theat ers lie close together, and patients can be intraoperatively transport ed from one room to the other. This retrospective analysis includes 55 patients with cerebral lesions, all of whom were surgically treated b etween March 1996 and September 1997. RESULTS: Thirty-one patients wit h supratentorial tumors were surgically treated (with navigational gui dance) in the conventional operating room, with intraoperative MRI for resection control. For 5 of these 31 patients, intraoperative resecti on control revealed significant tumor remnants, which led to further t umor resection guided by the information provided by intraoperative MR I. Intraoperative MRI resection control was performed in 18 transsphen oidal operations. In cases with suspected tumor remnants, the surgeon reexplored the sellar region; additional tumor tissue was removed in t hree of five cases. Follow-up scans were obtained for all patients 1 w eek and 2 to 3 months after surgery. For 14 of the 18 patients, the im ages obtained intraoperatively were comparable to those obtained after 2 to 3 months. Intraoperative MRI was also used for six patients unde rgoing temporal lobe resections for treatment of pharmacoresistant sei zures. For these patients, the extent of neocortical and mesial resect ion was tailored to fit the preoperative findings of morphological and electrophysiological alterations, as well as intraoperative electroco rticographic findings. CONCLUSION: Intraoperative MRI with the Magneto m Open provides considerable additional information to optimize resect ion during surgical treatment of supratentorial tumors, pituitary aden omas, and epilepsy. The twin operating theater is a true alternative t o a dedicated MRI system. Additional efforts are necessary to improve patient transportation time and instrument guidance within the scanner .