Investigation of histological heterogeneity based on the discrepancy between the hyperintense area on T2-weighted images and the accumulation area on 11C-methionine PET in minimally enhancing glioma

Abstract

IntroductionThe objective of the study was to investigate the correlation between differences between imaging modalities and histological heterogeneity in minimally enhancing glioma. MethodsA prospective study was performed in 11 patients with minimally enhancing glioma (<1 cm3 volume) in the T2 or FLAIR hyperintense (T2/FL+) area who simultaneously underwent 11C-methionine (MET)-PET, and had a volume-based discrepancy between the T2/FL+ area and MET accumulation (MET+) area (tumor to normal cortex (T/N) ratio ≥1.3) of >10%. The correlation between the imaging discrepancy and histological heterogeneity was investigated. ResultsThe average T/N ratio for the T2/FL+/MET+ area in grade II glioma (2.08 ± 0.4) was smaller than that in grade III (4.19 ± 2.4), whereas that for the T2/FL+/MET− area was similar in grade II (1.07 ± 0.2) and III (1.07 ± 0.1). The average T/N ratio for the T2/FL+/MET+ area in grade II and III was higher than that for the T2/FL+/MET− area (p < 0.0005 for grade II, p < 0.05 for grade III). In the T2/FL+/MET− area, 8 cases showed no neoplastic features, while the other 3 cases had neoplastic features with comparatively lower grade than the T2/FL+/MET+ area. The volumetric ratio of the MET+ area (16.8 ± 16.0 cm3) to the T2/FL+ area (41.5 ± 20.9 cm3) was 43.4%, and the volumetric difference in grade II cases (61.6%) tended to larger than that in grade III (50.6%). In immunohistochemical findings, the only MIB1 labeling index differed between grade II (5.5 ± 2.1) and III (23.2 ± 18.0) with significantly difference. In the T2/FL+/MET− area, 3 of 6 grade II gliomas had neoplastic features, whereas all 5 grade III gliomas had normal brain including one gliosis histologically. ConclusionThe discrepancy between the T2/FL+ and MET+ areas could reflect spatial heterogeneity in histological findings. An understanding of the correlation between imaging and pathology based on spatial heterogeneity may assist with appropriate diagnosis and treatment for patients with glioma.