INTRAOPERATIVE MRI TO CONTROL THE EXTENT OF BRAIN-TUMOR SURGERY

Purpose: The main aim of our study was to find out whether the combine d use of neuronavigation and intraoperative MRI can increase the rate of ''complete tumor removal''. The second aim was to characterize the different forms of surgically induced enhancement in order to differen tiate them from residual tumor. Materials and methods: Surgery was per formed in 18 patients with high-grade glioma. Using a neuronavigation device, the surgeons operated up to the point where they would otherwi se have terminated surgery. Intraoperative MRI was then performed to d etermine whether residual enhancing had been left behind and to update the neuronavigation device. If necessary, feasible surgery was contin ued. On days 1-3 after surgery early postoperative MRI (1.5 T) was per formed. The proportion of patients in whom the enhancing tumor was com pletely removed was compared with a series of 60 patients with gliobla stoma multiforme, who had been operated on using neither neuronavigati on nor intraoperative MRI. We also looked for and characterized differ ent types of surgically induced enhancement. Results: Intraoperative M RI definitely showed residual tumor in 6 of the 18 patients and result ed in ambiguous findings in 3 patients. In 7 patients surgery was cont inued. Early postoperative MRI showed residual tumor in 3 patients and resulted in uncertain findings in 2 patients. The rate of patients in whom complete removal of enhancing tumor could be achieved was 50 % a t the time of the intraoperative MR examination and 72 % at the time o f the early postoperative MR control. The difference in proportion of patients with ''complete tumor removal'' between the groups who had be en operated on using neuronavigation (NN) and intraoperative MRI (ioMR I) and those who had been operated on using only modern neurosurgical techniques except NN and ioMRI was statistically highly significant (F isher exact test; P = 0.008). Four different types of surgically induc ed contrast enhancement were observed. These phenomena carry different confounding potentials with residual tumor. Conclusion: Our prelimina ry experience with intraoperative MRI in patients with enhancing intra axial tumors is encouraging. Combined use of neuronavigation and intra operative MRI was able to increase the proportion of patients in whom complete removal of the enhancing parts of the tumor was achieved. Sur gically induced enhancement requires careful analysis of the intraoper ative MRI in order not to confuse it with residual tumor.