H3 K27-altered diffuse midline glioma in adults arising from atypical regions: Two case reports and literature review

• Published in: Radiology case reports Vol. 19; no. 1; pp. 200 - 206
• Main Authors: Sugii, Narushi, Ninomiya, Yuki, Akimoto, Yu, Tsurubuchi, Takao, Ishikawa, Eiichi
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier 01.01.2024
• Subjects: Adult diffuse midline glioma; Corpus callosum; H3 K27-altered; H3 K27M; Hypothalamus; H3 K27-altered; Adult diffuse midline glioma; Hypothalamus; Corpus callosum; H3 K27M
• ISSN: 1930-0433; 1930-0433
• DOI: 10.1016/j.radcr.2023.10.031

Diffuse midline glioma (DMG), H3 K27-altered, is a newly defined "pediatric-type," diffuse, high-grade glioma under current WHO classifications (updated in 2021). An essential diagnostic criteria of DMG is its occurrence in the midline structures; most intracranial DMG occurs in the brainstem or thalamus but can also occur in other midline structures. We experienced 2 adult cases of intracranial DMGs in areas other than the brainstem and thalamus that were initially difficult to diagnose. Case 1 was a 49-year-old man with extensive T2 high-signal lesions in the bilateral frontal lobes and corpus callosum on brain MRI. A Gd-based contrast medium partially enhanced the lesion and showed marked diffusion restriction, mimicking malignant lymphoma. Case 2 was a 24-year-old man who presented with paroxysmal olfactory abnormalities. The tumor extended mainly to the right temporal lobe, the right basal forebrain, and the bilateral hypothalamus, showing a T2/FLAIR mismatch sign suggestive of IDH-mutant astrocytoma without 1p/19q co-deletion. After a biopsy, both cases were properly diagnosed as DMG, H3 K27-altered (K27M-mutant). Diagnosing adult cases involving atypical midline structures is sometimes challenging before surgery; we discuss this phenomenon with both case details and a literature review.