Intracranial Retrograde Cerebrospinal Fluid Dissemination of H3 K27-altered Glioma.

Introduction: Diffuse midline glioma, H3 K27-altered (DMGHA), is an uncommon malignant primary brain tumor associated with a grave prognosis and limited treatment options. We report a unique case of an elderly woman who was initially treated for a right cerebellar DMGHA. She subsequently developed a distal recurrence at the septum pellucidum, hypothesized to be a result of retrograde cerebrospinal fluid (CSF) dissemination. Case History: A 72-year-old woman initially presented with headache and dizziness. The subsequent workup revealed a right cerebellar mass. A diagnosis of DMGHA was confirmed by histological studies and molecular profiling, and she was treated with gross total resection followed by protocol-based chemoradiation. At 12 months after surgery and treatment, surveillance imaging showed a new isolated enhancing mass in the septum pellucidum. She underwent another gross total resection with an anterior interhemispheric approach. Pathology confirmed a diagnosis of DMGHA. Conclusion: We report a novel case of recurrent distal spread of a right cerebellar DMGHA to the septum pellucidum. Although several putative mechanisms may be hypothesized to account for the very unique pattern of disease spread including simple multifocal disease, retrograde CSF dissemination may be the most likely mechanism. This is due to the lack of radiographic evidence for subcortical or hematogenous spread, and the interface between both enhancing masses and the CSF compartment.