 Cysts usually just contain fluid and are lined by either many layers of flat cells or column-shaped cells.Despite this, the presence of a cyst can cause problems similar to those of thymomas, by compressing nearby structures, and some may contact internal walls () and be difficult to distinguish from tumours.When cysts are found, investigation may include a workup for tumours, which may include CT or MRI scan of the area the cyst is suspected to be in.