A colloid cyst is a slow-growing benign tumor that makes up less than 1% of all intracranial neoplasms. It is a neuroepithelial cyst composed of a fibrous, epithelial-lined wall filled with a mucoid or dense hyloid substance. It is most commonly found in the anterior portion of the third ventricle, where it may cause obstructive hydrocephalus by blocking outflow of CSF from the lateral ventricles through the foramina of Monro. Average age of diagnosis ranges from 20-50 years. Many colloid cysts are less than 1 cm in size and are asymptomatic. Larger cysts associated with obstruction present with symptoms of intracranial hypertension or chronic hydrocephalus. These include headache, gait disturbance, disturbance in mentation, nausea and/or vomiting, and blurred vision. Emergent symptoms include papilledema, gait disturbance, hyperreflexia, and positive Babinski reflex. Imaging with CT or MRI typically demonstrates hydrocephalus of the lateral ventricles only.

Surgical removal is the treatment of choice. If the cyst is severely attached to it vicinity including structures such as fornix (important for memory), thalamostriate veins (occlusion leads to serious complications including stroke of the thalamus) and choroid plexus (with risk of bleeding), bilateral shunting can be considered. In this case, risks of shunt dependency, tumor progression, and sudden neurologic deterioration due to hypothalamic compression remain without surgical intervention. Therefore, surgical resection is the treatment of choice.