Diffuse midline glioma, H3 K27-altered, forming a suprasellar mass: A case report.

Diffuse midline glioma, H3 K27-altered (DMG), is an extremely aggressive tumor that mainly arises in midline structures such as the thalamus, brainstem, and spinal cord in children and young adults. We report a rare adult case of DMG presenting as a suprasellar mass. A 56-year-old man presented with progressive visual impairment over 2 months. Magnetic resonance imaging (MRI) revealed a lobulated mass centered on the optic chiasm and extending from the suprasellar region to the anterior aspect of the midbrain, with involvement of both optic tracts and the hypothalamus. Subtotal resection was performed, and histopathological and molecular genetic examination demonstrated a diffuse glioma harboring an H3F3A p.K28M (H3.3 K27M) mutation, leading to the diagnosis of diffuse midline glioma, H3 K27-altered (H3.3 K27M-mutant subtype), central nervous system WHO grade 4. Based on the clinical presentation and MRI findings, the tumor was considered to originate from the optic chiasm. However, autopsy findings suggested that the tumor likely originated from the hypothalamus and secondarily involved the optic chiasm. Despite postoperative chemoradiotherapy, the patient died approximately 5 months after symptom onset. Although DMG occurring in the suprasellar region with optic tract involvement is very rare, it should be considered in the differential diagnosis of suprasellar masses.