NI-20 IS GLIOMATOSIS CEREBRI DIAGNOSED AS GRADEII IN NEUROIMAGING A POTENTIALLY GRADEII GLIOMA?

The 2007 World Health Organization (WHO) classification defined gliomatosis cerebri (GC) as a rare entity and an extensively infiltrating diffuse glioma involving three or more cerebral lobes. Although the revised 2016 WHO classification removed GC as a separate glioma entity due to the common histopathological findings shared with other gliomas, GC exhibits a distinct growth pattern and worse prognosis compared with other grade-matched gliomas. We retrospectively reviewed five patients with GC and five patients with insulo-opercular diffuse astrocytoma (IODA) who underwent both proton magnetic resonance spectroscopy (MRS) and [(11)C]-methionine positron emission tomography (MET-PET). The patients were diagnosed with GC or IODA by T2-weighted magnetic resonance imaging /fluid-attenuated inversion recovery from April 2014 to August 2019 at our institution. The locations of lesions where single-voxel MRS to measure the N-acetylaspartate (NAA)/choline (Cho) ratio and MET-PET to measure the tumor/normal (T/N) ratio were performed were the same in every patient. The mean age of all patients was 46.3±13.7 years. The mean ages of the GC (three males and two females) and IODA (two males and three females) groups were 54.0±14.0 and 38.6±8.7 years, respectively. The mean NAA/Cho ratios in the GC and IODA groups were 1.010±0.441 and 0.594±0.449, respectively. The mean T/N ratios in the GC and IODA groups were 1.201±0.050 and 1.169±0.009, respectively. The higher NAA/Cho ratio in the GC lesions may reflect the abundance of normal neural tissue in GC compared with IODA. Nonetheless, the T/N ratios of the two groups were comparable. The discrepancy suggests that GC cells have higher tumor metabolic activity than IODA cells. Therefore, when GC is simply classified as grade II glioma based on neuroimaging diagnosis, the possibility of underestimating its malignant potential at the single-cell level should be considered.