IMG-12. Magnetic Resonance Spectroscopy Utilization in a Rare Adult Case of Diffuse Midline Glioma, H3 K27 Altered, with Low Levels of MGMT Methylation

Abstract Diffuse midline glioma, H3 K27 altered (DMG), is an infiltrative glioma subtype characterized by mutations in the gene H3F3A. DMGs exhibit a diffuse growth pattern and commonly arise in the thalamus, brainstem, or spinal cord. Highly aggressive and associated with poor survival, DMG accounts for roughly 10% of pediatric brain tumors, representing the leading cause of pediatric cancer-related deaths. A diagnosis of DMG is rare in adulthood. This case report utilizes chart review of the history, physical examination, laboratory tests, imaging findings, and pathology samples acquired during this patient’s hospital admission. We present a case of an atypical high grade glioma (HGG) in a young woman with a family history of Glioblastoma Multiforme and Coffin-Siris Syndrome. This patient presented with acute unilateral facial and upper extremity weakness and numbness. Initial neuroimaging ruled out an intracranial hemorrhage or cerebral infarct. Magnetic Resonance Imaging revealed lesions located in the left thalamus, right cerebellum, and left caudothalamic region with intraventricular spread, diffusion restriction along the ependyma of the lateral ventricles, and infratentorial leptomeningeal enhancement. Magnetic resonance spectroscopy (MRS) was utilized to better analyze these irregular lesions. Suboptimal voxel placement initially yielded nondiagnostic spectroscopy results. When voxels were selected precisely by an attending radiologist, the resulting metabolite peaks and ratios correlated to a CNS lymphoma, or a necrotic infiltrative HGG. Pathology characterized the mass as a CNS WHO grade four diffuse HGG with extensive necrosis and a H3 K27 alteration, indicating a final diagnosis of a DMG. This case points to possible relationships between subclinical SMARCA4 mutations and the early development of rare gliomas, as well as low levels of MGMT methylation. This case demonstrates the importance of teamwork between radiologists and technologists in voxel selection and a need for scientific consensus to improve the diagnostic certainty of MRS in rare tumor morphologies.