Oligodendroglioma with ganglioglioma-like maturation: the histopathological diagnostic challenge of a brain neoplasm with aberrant neuronal component - A case report and review of the literature.

Background: Oligodendroglioma with ganglioglioma-like maturation is a rare entity not included in the 2016 World Health Organization Classification of Tumors of the Central Nervous System. To date, only a few cases were described in the literature. We report a case of this tumor, along with a review of the previous case reports/ series. Case Description: A 63-year-old man with a left frontal mass and a 2-month history of seizures underwent surgical resection in our center. Grossly, the specimen appeared as a yellowish mass with prominent hemorrhagic component. Microscopically, the lesion was composed by small round cells often surrounded by a clear halo and, near the hemorrhagic area, by scattered large cuboidal cells with vesicular nuclei and prominent eosinophilic nucleoli. On immunohistochemical stains, both cells components tested positive for ATRX, p53, and GFAP; larger ganglion-like cells showed synaptophysin and chromogranin-A expression. IDH1 codon 132 mutation, 1p-19q-codeletion, and MGMT methylation were observed. Eventually, a diagnosis of oligodendroglioma (the WHO grade II) with ganglioglioma-like maturation was rendered. The patient received adjuvant chemotherapy and is currently alive and asymptomatic. Conclusion: Recognition of ganglioglioma-like maturation in oligodendrogliomas may prevent undertreatment of these neoplasms. To this end, fluorescence