Spectral changes in postoperative MRS in high-grade gliomas and their effect on patient prognosis

The aim of the study was to find differences in magnetic resonance spectroscopy (MRS) which might facilitate differential diagnosis between tumour regrowth and a remnant tumour with present postradiation changes or postradiation necrosis in the vicinity of the postoperative bed, based on the assessment of the dynamics between two MRS, i.e. preoperative and postoperative scanning, performed at 6 months after surgery. Therefore, in 9 patients with high-grade gliomas, MRS spectra were obtained. Subsequently, a partial tumour resection was done in 5 patients, and 4 subjects underwent a gross total resection. On the second MRS the voxel was placed on an observed contrast enhancement area. The tumour regrowth onset was established by comparing the results of control MRI with postoperative CT scans, and also on the basis of changes in clinical condition as well as a further follow-up, including MRI studies. In patients with tumour regrowth Cho/NAA and Lac/Cr ratios increased and the NAA/Cr ratio decreased between the two MRS studies; in the patients without regrowth, the ratio changes were inverse. In both groups, a decrease in Cho/Cr ratio was observed. In a univariate analysis the presence of tumour regrowth and an increase in Cho/NAA ratio between the two MRS were correlated with a shorter further survival time; a tendency to shorter further survival time was noted with decrease in NAA/Cr ratio. In conclusion, MRS is a diagnostic tool which, on the basis of direction of changes in the value of metabolite ratios, helps additionally confirm the diagnosis of glioma regrowth. In the case of a visible contrast enhancement area on the postoperative MRI with observed concomitant increase in Cho/NAA ratio and decrease in NAA/Cr ratio between pre- and postoperative MRS examinations, preliminary suspicion should be that of glioma regrowth rather than of remnant tumour after surgery or postradiation lesions.