Diencephalic pediatric low-grade glioma harboring the BRAF V600E mutation presenting with various morphologies in sequential biopsy specimens

A 5-year-old boy underwent biopsy of an intra-axial calcified tumor in the hypothalamus, which was incidentally found. Based on the presence of ganglion-like cells combined with glial cell element, the pathological diagnosis was ganglioglioma. Because the tumor grew gradually in size over the next 2 years, he underwent chemotherapy with temozolomide. However, at 8 years of age, the boy developed hydrocephalus and the cystic lesion had re-grown. Endoscopic cyst fenestration and tumor biopsy was performed, and pathological diagnosis was tentatively oligodendroglioma based on the presence of tumor cells with a perinuclear halo. At 10 years of age, hydrocephalus recurred and the cystic lesion had re-grown. A second round of endoscopic cyst fenestration and tumor biopsy led to a pathological diagnosis of pilocytic astrocytoma due to a biphasic appearance with areas of dense tumor cells and microcystic areas, tumor cells with eosinophilic processes, and the presence of an eosinophilic granular body. Genetic analysis of the first biopsy successfully identified the BRAF V600E mutation. Because pathological diagnosis of diencephalic low-grade glioma harboring BRAF V600E would be sometimes difficult due to pathological variations, pathological diagnosis should be performed under the consideration of molecular diagnosis of BRAF V600E for optimal diagnosis and treatment.