The colloid cyst of the third ventricle is a benign dysembryoplastic tumor, very rare, representing 0.2 to 2% of brain tumors. It is a tumor mainly of adults in their 30s and 40s, with a male predominance. It is a rounded cystic lesion, a few millimeters to several centimeters for the largest, containing a gelatinous substance more or less liquid. The main symptom is HTIC. Many colloid cysts are asymptomatic and are discovered incidentally. MRI is...