A cyst is a closed sac having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, the cyst could go away by itself or will have to be removed using surgery.
A syrinx in the spinal cord or brainstem is sometimes inaccurately referred to as a cyst.
Carcinoid Tumor Arising in a Tailgut Cyst of the Anorectal Junction With Distant Metastasis: A Case Report and Review of the Literature
May 01, 2004; Tailgut cyst is a rare congenital presacral lesion and is believed to arise from the persistent remnants of the postanal gut....