11C–methionine PET/CT in meningiomas

Abstract

Currently, positron emission tomography (PET) is the standard imaging modality in neuro-oncology for gliomas and metastatic lesions. The experience of PET application in meningiomas, the most frequent primary CNS neoplasms, is much less, and the interpretation of the study results has a number of differences. The aim of the study was to evaluate the possibility and peculiarities of PET application in meningiomas based on our own clinical experience and literature review. The study included 70 patients with 77 meningiomas who underwent PET/CT with 11C-methionine. The mean age at the time of examination was 57.4 years (19–86 years). The main evaluation parameter, the tumor-to-brain ratio (TBR) of 11C-methionine (11C–MET) averaged 3.13 (1.00–10.66). Meningiomas were characterized by high 11C–MET TBR, with 89.6% of cases having TBR greater than 1.5. In histologically verified WHO grade 1, 2, and 3 meningiomas, the median TBR was 4.06 [3.04, 4.57], 2.32 [2.12, 3.69], and 4.29 [2.60, 5.10] and did not differ significantly between groups. Meanwhile, in histologically unresectable slow-growing or non-growing incidental meningiomas, TBR of 11C–MET was significantly lower than in WHO grade 1 and 3 meningiomas. There was no significant difference in the accumulation index between irradiated meningiomas with tumor growth control (3.81 [2.97, 3.98]) and recurrence (3.62 [2.60, 4.30]). When irradiated and non-irradiated meningiomas of WHO grade 1, 2 and 3, as well as the combined group of grade 1–3 tumors were compared, no significant differences in 11C–MET TBR were found. The use of PET/CT in meningiomas has a number of important features. Meningiomas are characterized by high TBR of 11C–MET. According to our data PET/CT with 11C–MET does not allow differentiating between meningiomas of different degrees of malignancy – 1, 2 or 3 according to WHO. With effective radiotherapy, meningiomas show partial reduction of TBR or remain stable. Even with prolonged growth control after radiation treatment, meningiomas may still have high TBR of 11C–MET. When comparing growing and stable meningiomas, irradiated and non-irradiated tumors, no significant differences in TBR of 11C–MET are found.