[A case of gangliocytoma: a six-year follow-up of cyst formation].

We report a case of gangliocytoma at a cortical and subcortical area in the right parietal lobe. The patient had a generalized seizure at 11 years of age. The MRI shows an ill-demarcated high intensity area in T2 weighted images including an enhancing tumor of 10 mm in diameter. At first, the tumor was carefully followed up because of its small size and the surgical risk. Three years after the onset, a cyst formed at the area of the brain edema adjacent to the tumor. The cyst gradually grew to 21 mm in diameter, the edema had disappeared, and the size of the tumor became smaller (7 mm) within the next 3 years. A mural nodule, jelly-like tumor with calcification was totally removed and diagnosed as gangliocytoma. The cyst fluid was watery-clear, its wall did not contain any tumor. This is the first report of a six-year follow-up of cyst formation of gangliocytoma supporting the concept that edema is a precursor to central nervous system peritumoral cyst formation based on the similar observation of hemangioblastomas.