Incidental meningiomatous component within an intraventricular metastasis: A rare intraventricular collision tumor

Background: Intraventricular cerebral metastases are rare. Collision tumors comprising metastatic carcinoma with a meningiomatous component are exceptional, particularly within the ventricular system. Case Description: A 79-year-old female with a history of endometrial serous carcinoma presented with progressive cognitive decline and gait instability. Magnetic resonance imaging demonstrated a large left occipital mass with intraventricular extension and surrounding edema. She underwent resection. Histopathology showed a papillary tumor consistent with metastatic high-grade serous carcinoma, and within the specimen, a discrete meningiomatous focus was identified, compatible with a collision tumor. Postoperatively, she recovered without new deficits. Conclusion: This case highlights an uncommon intraventricular collision tumor formed by metastatic high-grade serous carcinoma and an incidental meningiomatous component, underscoring the importance of thorough sampling and immunohistochemistry for ventricular masses in oncologic patients.