Preoperative Evaluation of Malignancy of Glioma by Thallium-201 SPECT, Proton MRS and 18F-fluorodeoxy-glucose PET

Abstract

Objective : We studied preoperative malignancy evaluation of glioma by thallium-201 SPECT (Tl-SPECT), proton MRS (MRS) and 18F-fluorodeoxy-glucose PET (FDG-PET). Methods : Twenty-seven patients with astrocytic tumors (diffuse astrocytoma (A) : 8, anaplastic astrocytoma (AA) : 10, glioblastoma (GB) : 9) were retrospectively studied. FDG-PET was assessed as the visual metabolic grading scale (MG Scale) in 9 cases. The Tl index was expressed as the count rate of the tumor site to the count rate over the contralateral normal region in 25 cases. MRS was evaluated as the metabolite ratios of choline/creatine (Cho/Cr) and Cho/N-acetylaspartate (NAA), and as the presence of lactate and lipid metabolites in 23 cases. Results : As the malignancy grade of the glioma rises, so too did the MG Scale of FDG-PET and Tl index (PET MG Scale (A : Gr. 1; 2 cases, Gr. 2; 2 cases, AA : Gr. 1; 1 case, Gr. 2; 1 case, GB : Gr. 2; 2 cases, Gr. 3; 1 case), Tl index : A : 1.29±0.22, AA : 1.97±0.44, GB : 3.42±1.38). Metabolite ratios of Cho/Cr and Cho/NAA in the high-grade gliomas were higher than those in the low-grade gliomas, however, those of GB were lower than those of AA, maybe due to difficulty in the spectroscopic voxel selection (Cho/Cr : A : 1.86, AA : 2.96, GB : 2.73, Cho/NAA : A : 2.90, AA : 6.37, GB : 5.57). Both lactate and lipids presented in the high-grade glioma cases. Proliferative potential as measured by MIB-1 index mostly correlated with the Tl index significantly (p=0.0002). Conclusion : We were able to evaluate the malignancy grade of gliomas preoperatively by using FDG-PET, Tl-SPECT and MRS, however, we also need to understand the pitfalls of each of these examinations respectively.