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Diffuse hemispheric glioma, H3 G34-mutant (DHG), is a newly defined pediatric-type tumor in the 2021 WHO classification of central nervous system (CNS) tumors. DHGs harbor missense mutations at codon 35 of H3F3A (H3.3 G35R/V mutations) and exhibit diverse histopathological features, such as glioblastomas or CNS embryonal tumors. Regardless of histological variation, they demonstrate uniform immunohistochemical and molecular findings: Olig2 negative, ATRX loss, p53 positive, and MGMT promoter methylated. These tumors occur predominantly in the cerebral hemispheres of adolescents and young adults, while they are extremely rare in middle-aged and elderly individuals. Here, we report a middle-aged case of DHG with prominent perivascular invasion. The tumor initially demonstrated a focal glioblastoma-like area, whereas the recurrent tumor predominantly showed perivascular spread of spindle cells. We reviewed previously reported DHG cases in middle-aged and elderly patients and compared their clinicopathological features with those of adolescents and young adults.