Cerebellar high-grade glioma with H3 K27M mutation: illustrative case

<jats:sec><jats:title>BACKGROUND</jats:title><jats:p>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 <jats:italic>Classification of Tumours of the Central Nervous System</jats:italic>. They are aggressive pediatric tumors with a poor prognosis but have also been reported in adults.</jats:p></jats:sec><jats:sec><jats:title>OBSERVATIONS</jats:title><jats:p>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 <jats:italic>HIST1H3B</jats:italic> 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.</jats:p></jats:sec><jats:sec><jats:title>LESSONS</jats:title><jats:p>When a glioblastoma shows localization or dissemination patterns different from those of typical glioblastoma, an H3 K27M-mutant glioma should be suspected.</jats:p></jats:sec>