Oligodendroglial hamartoma: a potential source of misdiagnosis for oligodendroglioma

Various subtypes of intracerebral hamartomas, associated with seizure disorders, have long been described. We describe a cerebral hamartoma placed in the left frontal lobe, associated with drug-resistant epilepsy, composed exclusively of mature oligodendroglial cells. The patient was a 27-year-old right-handed male presenting with severe epileptic encephalopathy and symptoms of behavior dysfunction (disinhibition, rage attacks) associated with a left frontal lesion. Magnetic resonance imaging revealed a small area iso-hypointense compared to the gray matter in T1-weighted sequences not enhancing after gadolinium contrast injection in the left frontal site. On histology, a cortical lesion composed of large aggregates of oligodendroglial cells, with round central nuclei and clear perinuclear halos, was observed. Neither mitotic figures nor necrosis were present. Reactivity for Ki67 and P53 was not found. The lesion was well demarcated from the adjacent brain parenchyma and perineuronal satellitosis was not observed in the cortex. In conclusion, albeit extremely rare, recognition of oligodendroglial hamartoma and its distinction from other epileptogenic lesions as dysembryoplastic neuroepithelial tumor or above all oligodendroglioma have important therapeutic and prognostic implications.