Walsh & Hoyt: Cysts and Tumors Involving the Third Ventricle

The third ventricle is the narrow, funnel-shaped, midline cavity between the two lateral symmetric halves of the diencephalon. It communicates at its anterosuperior margin with each lateral ventricle through the foramen of Monro and posteriorly with the fourth ventricle through the cerebral aqueduct (of Sylvius). Zulch found that the most common tumors originating within the third ventricle were colloid cysts, followed by ependymomas, choroid plexus papillomas, epidermoids, and meningiomas. Rarely, a third ventricular hemangioblastoma is reported in patients with the von Hippel-Lindau syndrome. Tumors that originate outside the third ventricle, including astrocytomas, oligodendrogliomas, neurocytomas, and ganglioneuromas, occasionally infiltrate its walls, floor, or roof and enter its cavity. Arachnoid cysts that originate in the suprasellar region may also extend upward and either compress or invade the third ventricle. Finally, lesions of the pineal gland may encroach upon the posterior portion of the third ventricle.