>99% wedged into foramen of Monro
<1% other sites include lateral, fourth ventricles, cerebellum and extra-axial( prepontine and meninges).
1-2 mm up to 3 cm with mean size of 15 mm.
0.5-1.0% of primary brain tumors and 15-20% of intraventricular masses.
Cyst contents gelatinous( colloid) material with variable viscosity with or without necrotic leukocytes and cholesterol clefts.
On non contrast CT- two thirds hyperdense, one third iso/hypodense with or without hydrocephalus. Rarely can have hemorrhage and calcification.
On contrast CT- doesn’t enhance and rarely rim enhancement.
On DWI- no restricted diffusion.
Most common presentation is headache(50-60%)
Acute foramen of Monro obstruction may lead to rapid onset hydrocephalus, herniation and death