Colloid Cysts of the Third Ventricle

Colloid cysts are rare benign tumors that almost exclusively arise near the foramen of Monro in the third ventricle. They represent approximately 1% to 2% of all intracranial tumors. Although many colloid cysts are asymptomatic, they may obstruct the foramen of Monro and cause obstructive hydrocephalus and, in certain cases, rapid clinical deterioration and death. The natural history of colloid cysts is not completely understood, but it is widely accepted that asymptomatic cysts may be observed whereas symptomatic cysts should be surgically resected soon after symptoms develop. Because they are located in the center of the brain in the third ventricle, a number of different surgical approaches may be used to reach the cyst, including multiple open and endoscopic procedures. This chapter provides an overview of colloid cysts, their natural history, risk factors, and imaging characteristics. The proper management of colloid cysts, including many different surgical options, is outlined, and important surgical anatomy is detailed.