Diffuse midline glioma H3K27-altered with thoracic epidural metastasis: illustrative case.

backgroundDiffuse midline glioma (DMG) H3K27-altered is a newly recognized diffuse high-grade tumor entity in the 5th edition of the WHO classification of CNS tumors. Spinal extradural metastasis is extremely rare in patients with DMG H3K27-altered, while the occurrence of spinal intramedullary DMG, intradural dissemination, and osseous metastasis has been reported. OBSERVATIONS: The authors report the case of a 6-year-old female presenting with acute-onset urinary retention and paraplegia, who was found to have a pontine DMG, an intradural mass at the level of T1-6, and an extradural lesion at T6-9. The thecal sac was severely compressed by the extradural mass; thus, a T6-9 laminectomy and extradural tumor resection were performed. After the procedure, an amelioration of weakness was observed. The patient was treated with radiotherapy to the spine. Pathology revealed an increase in chromatin, the proliferation of atypical cells, and microvascular proliferation. The H3K27 mutation was confirmed. LESSONS: This case demonstrates an operative view in the metastasis of DMG H3K27-altered to the spinal epidural space without visceral or osseous metastasis. The possibility of spinal epidural metastasis and its surgical treatability should be considered if patients with DMG present spinal cord symptoms. https://thejns.org/doi/10.3171/CASE25249.