A cyst is a closed sac, having a distinct membrane and division compared to the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (not unlike the manner in which water molecules group together, forming a bubble); however, the distinguishing aspect of a cyst is the cells forming the “shell” of such a sac, being distinctly abnormal (in both appearance and behaviour) when compared to all surrounding cells for that given location. It may contain air, fluids, or semi-solid material.

see Tumor cyst.

Arachnoid cyst.

Choroid plexus cyst of the third ventricle.

Colloid cyst.

Cystic lesion

Cystic tumor

Dermoid cyst.

Epidermoid cyst.

Neuroglial cyst.

Pineal cyst.

Cystic lesions in the atrium (trigone) of the lateral ventricle may become symptomatic due to obstruction of physiological CSF circulation and/or from mass effect on adjacent structures.

Synovial cyst.

Tarlov cyst

Juxtafacet cyst.