Imaging Clues That Raise Suspicion for Diffuse Midline Glioma

In this episode, Dr. Chong sets up the clinical reality that patients usually present with imaging before tissue and asks Dr. Shonka how MRI findings should shape suspicion for DMG. Dr. Shonka emphasizes that even glioblastoma is rare — “half of 1% of all cancers in adults” — and that DMG is rarer still, so close work with neuroradiology and neuropathology is essential to avoid misclassifying an H3 K27M-altered DMG as a glioblastoma. The midline location is the first clue: thalamus, brainstem, and the spinal cord, particularly in patients in their 40s or younger. Compared with glioblastoma, DMG typically shows less contrast enhancement (sometimes only faint, or even non-enhancing), less peritumoral edema (because the blood–brain barrier is more intact), and lower perfusion on MRI. Glioblastoma, in contrast, is more often hemispheric, with the prototypical ring enhancement around a necrotic center, significant peritumoral edema, and elevated relative cerebral blood volume (rCBV) on perfusion mapping. Dr. Shonka highlights the value of advanced sequences, such as perfusion imaging and apparent diffusion coefficient (ADC) mapping, for initial differentiation and for distinguishing recurrent tumor from treatment effect over time, while noting that not every center has perfusion routinely available. She closes by underscoring that imaging features in DMG are highly variable, that imaging only generates the hypothesis, and that tissue with molecular confirmation remains the basis of diagnosis.

In the next episode, “Molecular Testing in Newly Diagnosed Glioma,” Dr. Chong walks through the essential workup, with attention to limited-tissue scenarios in midline tumors.