10323-CS-26 A Case of Diffuse Midline Glioma Presenting with Peritoneal Dissemination Following Ventriculoperitoneal Shunt Placement

Abstract Background Diffuse midline glioma (DMG), characterized by the H3K27M mutation, is a WHO Grade 4 tumor primarily affecting midline structures such as the thalamus and brainstem. While ventriculoperitoneal (VP) shunting is often required for associated hydrocephalus, peritoneal dissemination of DMG via VP shunt is extremely rare, with only a few reports to date. Case Presentation A man in his 30s presented with headache and visual disturbance. MRI revealed a hypothalamic tumor with obstructive hydrocephalus. A VP shunt was placed, followed by endoscopic biopsy confirming a diagnosis of DMG with H3K27M mutation. The patient received focal radiation therapy with concurrent and maintenance temozolomide. Eight months post-shunt, he developed abdominal distension. Imaging revealed ascites, and laparoscopic peritoneal biopsy was performed along with peritoneal port placement. Histopathology confirmed peritoneal dissemination of DMG. Additionally, intraventricular dissemination was observed 9 months after shunting. Discussion This case highlights a rare instance of peritoneal dissemination of DMG following VP shunt placement. The tumor’s propensity to shed cells into the cerebrospinal fluid suggests that shunt-mediated spread is a plausible mechanism. Although leptomeningeal spread of DMG is known, peritoneal metastasis remains exceedingly uncommon. This case adds to the limited literature suggesting the potential risk of tumor cell dissemination through VP shunting in midline gliomas. Conclusion We report a rare case of DMG with peritoneal dissemination following VP shunt surgery. Clinicians should be aware of this potential complication, especially in tumors known to shed malignant cells into CSF. Further accumulation of similar cases is needed to better understand the mechanisms and clinical implications of shunt-mediated dissemination in DMG.