Diffuse midline glioma H3 K27M-mutant is a distinct subtype of glial tumors newly introduced in the revised fourth edition of the World Health Organization Classification of Tumours of the Central Nervous System. They are aggressive pediatric tumors with a poor prognosis but have also been reported in adults.
The authors present the case of a man in his 60s who presented with rotatory vertigo, taste disorder, and right facial paralysis. Magnetic resonance imaging showed a tumor expanding from the cerebellum to the pons, which was histologically identified as glioblastoma, grade IV, IDH wild type. After tumor resection, the patient received chemoradiotherapy but showed only a partial response. His condition gradually worsened, and he died of progressive disease 12 months postoperation, after which an autopsy was performed. Tumor cells with a high nuclear-to-cytoplasm ratio were immunohistochemically analyzed and found to test positive for H3 K27M and negative for H3 K27me3. Furthermore, mutational analysis revealed HIST1H3B K27M mutation, and the tumor was finally identified as a high-grade glioma H3 K27M-mutant. The tumor invaded widely along the cerebral ventricle and disseminated to the spinal cord.
When a glioblastoma shows localization or dissemination patterns different from those of typical glioblastoma, an H3 K27M-mutant glioma should be suspected.