The aim of this study is to compile the most suitable MRI examination protocol for early post-operative check-ups of patients after surgery for high-grade glioma. The protocol should aim at differentiating surgically- induced (benign) post-contrast tissue enhancement from the pathologic enhancement representing residual tumorous tissue. Materials and Methods. 34 patients (22 males, 12 females) with high-grade gliomas were examined between January 1997 and November 2003. Unenhanced and contrast-enhanced MRI scans were performed within 72 hours after surgery in all patients. Results. Unenhanced early post-operative MRI examinations proved the presence of T1 hyperintensity within the operative field in all patients. By means of in vitro MRI experiments, we proved that exposure of fresh blood to atmospheric oxygen accelerates the conversion of oxy- and deoxyhemoglobin to T1 hyperintense methemoglobin. The presence of hemostatic material (Surgicel) within the resection cavity probably facilitates the degradation of hemoglobin as well. We observed linear and choroidal type of enhancement in all patients (100 %), meningeal type in 86% and nodular in 86% as well. The nodular type of enhancement was observed in all the patients with proven residual tumor, except for one case where benign surgically-induced nodular enhancement was present. Conclusion. Exposure of brain tissue to atmospheric oxygen during surgery and presence of hemostatic material (Surgicel) participate in early occurrence of T1 hyperintensity in the operation area. The presence of nodular post-operative enhancement always rises the suspicion of residual tumor. The comparison of pre-operative and post-operative MRI findings is the most important way to differentiate residual tumor from benign, surgically-induced nodular enhancement.

        Key words: high-rate gliomas, radiology imaging methods, MRI, early postoperative check-up