| Discussion: A colloid cysts is a benign epithelial cyst that usually arise from the inferior aspect of septum pellucidum and protrude into the anterior portion of the third ventricle between columns of fornix. There comprise 0.5 - 3% of all primary brain tumors, 15-20 % of intraventrcular neoplasm and almost excusively found within the third ventricle at the formen of monroe, although?there are reports of colloid cysts at unusual locations such as lateral ventricle and posterior fossa. They generally present in the 3rd?5th decade?(30 - 40%), although, they can present in extremes of age. The vast majority of colloid cysts are found incidentally on radiograph?and are asymptomatic; when they are sympotmatic, they present acutely with manifestation of ventricular outflow obstruction and consequent obstructive hydrocephalus. The primary presenting complaint is headache. The headaches are classically intermittent, episodic, sometimes intense and severe. They also tend to be positional. This headache is decreased on lying down, which is unusual for a headache?secondary to an intracranial space occupying lesion. Associated symptoms include vertigo, memory deficit, diplopia and behavioral disturbances and sudden death. The clinical finding of headaches is due to transient obstruction secondary to ball valve mechanism at the foramen of Monro. On CT, colloid cysts appear as a unilocular lesions that is present at the roof of the third ventricle and mostly?are hyperdense; isodense or hypodense lesions tend to be very uncommon; calcifications also tend to be uncommon.On MR, colloid cysts have high T1 signal, low T2 signal and rarely demonstrate thin rim enhancement on T1 with gadolinium contrast. Colloid cysts tend to enlarge over time and if resection is required, this can be done using transcallosal surgery. | 
ANATOMY - FORAMEN OF MONROE LESION
