18F-FMISO accumulates in glioblastoma multiforme but not in grade III or less malignant gliomas

Objectives 18F-fluoromisonidazole (FMISO) accumulates in hypoxic peri-necrotic tissues. Since necrosis is a pathological landmark in discriminating GBM (WHO grade IV) from nonGBM (grade III or less), FMISO PET may have a potential to differentiate GBM from nonGBM. The purpose of this study was to evaluate diagnostic value of FMISO, in comparison with that of FDG.

Methods Twelve glioma patients (M:F=6:6, age 54±15 years old), consisting of 10 preoperative cases and 2 postoperative recurrent cases, underwent both FMISO PET (400MBq, 4hr interval) and FDG PET (400MBq, 1hr interval) within a week. In qualitative analysis, a higher uptake in the tumor than surrounding tissue was defined as positive. Semiquantitative measurements including SUVmax and tumor-to-normal ratio (TNR) were statistically analyzed. TNR was calculated by SUVmax/[SUVmean of contralateral frontal cortex]. PET findings were compared with WHO grading and existence of necrosis in surgical specimens.

Results Pathological diagnosis was GBM in 6 and nonGBM in 6 cases (grade III:II = 4:2). Necrosis was found in all the GBMs but not in nonGBMs. In qualitative analysis, all the GBM cases showed positive FMISO uptake in the tumor (6/6), while all the nonGBM cases showed no uptake (0/6, P<0.01). In contrast, FDG was positive in 6/6 of GBMs and in 4/6 of nonGBMs (P=NS). Both SUVmax and TBR of FMISO were higher in GBM than in nonGBM (SUVmax: GBM 2.98±0.38 vs nonGBM 1.55±0.47, P<0.001; TNR: 3.24±0.44 vs 1.64±0.26, P<0.001), whereas neither SUVmax nor TNR of FDG showed a significant difference (SUVmax: 5.79±1.38 vs 9.32±7.39, P=NS; TNR 1.39±0.41 vs 1.41±0.98, P=NS).

Conclusions FMISO PET successfully discriminate GBM from less malignant gliomas, while FDG PET could not do in this study population. Demonstrating ischemic tissues with FMISO helps glioma grading, which affects prognosis and treatment strategy