Diffuse leptomeningeal glioneuronal tumor (DLGNT) is characterized by widespread leptomeningeal lesions with focal parenchymal involvement. We present a child with a large intramedullary spinal cord lesion, whose biopsy revealed a biphasic astrocytic tumor consistent with pilocytic astrocytoma. Next-generation sequencing revealed a KIAA1549-BRAF fusion, 1p/19q co-deletion, and no IDH1 mutation. Methylation profiling demonstrated a calibrated class score of 0.98 for DLGNT. Despite morphologic similarities to pilocytic astrocytoma and lack of oligodendroglial/neuronal components or leptomeningeal dissemination, the molecular profile definitively classified the tumor as DLGNT. This case highlights the importance of molecular and genetic testing in diagnosing pediatric central nervous system tumors.