Hi.. Tornwaldt's cyst refers to a rare cyst like structure seen behind the pharynx/adenoids. It is a remnant of a structure that was initially present during development of the fetus. The structure used to form a connection between what is known as the vertebral spine and the spinal cord now... This connection usually regress as the fetus grows.. Some time when it does not completely regress it can be seen as a cyst in the MRI scan.. It is most often an incidental finding and does not cause any problems.. Problems occur when this cyst gets infected when it has to be treated by a minor surgical treatment..