We studied a frontal lobe subcortical cystic
tumor that had been resected from a 13-year-old girl with a 3-year history of intractable partial seizure. Currently, more than 13 years after surgery, the patient remains recurrence-free and has no neurological deficits. Histological examination showed that the
tumor was non-infiltrating and paucicellular with a mucinous matrix, and consisted of fairly uniform small cells with round to oval nuclei. Within the mucinous matrix, the
tumor cells were often arranged in pseudorosettes around small blood vessels. Mitotic activity and
necrosis were absent, with a Ki-67 labeling index of <1%. Based on the immunohistochemical and ultrastructural findings, the constituent
tumor cells were considered to be those of
oligodendroglioma, including mini-gemistocytes and gliofibrillary oligodendrocytes. No neuronal elements were identified. Features of
cortical dysplasia (FCD Type 1) were evident in the cortex covering the lesion. The surrounding white matter also contained a significant number of ectopic neurons. The entire pathological picture appeared to differ somewhat from that of ordinary
oligodendroglioma (WHO grade II). Considering the clinical and pathological features, the present unusual
oligodendroglioma appeared to represent a previously undescribed form of
oligodendroglioma (WHO grade I) lying within the spectrum of dysembryoplastic
neuroepithelial tumor (
DNT; WHO grade I). Simultaneously, the present
oligodendroglioma also raises the question of whether or not oligodendrocyte-like cells of DNTs truly show neurocytic differentiation.