Indolent presentation of a diffuse midline glioma, H3 K27-altered

Diffuse midline glioma (DMG), H3 K27-altered, are aggressive central nervous system tumors which are universally fatal, with a median survival of 8-12 months after diagnosis. Here, we present a patient who was incidentally found to have a lesion, concerning for tumor, within the right thalamus on brain magnetic resonance imaging at 2 years of age. Twelve years later, subsequent imaging showed that the lesion had enlarged, with biopsy consistent with DMG harboring an H3 K27M mutation. This case illustrates an unusual presentation of a DMG, H3 K27-altered, with an indolent course. Such findings highlight the fact that more research is needed to understand what factors may contribute to these tumors' malignant course.