A ganglion cyst is a non-cancerous lump, often on the tendons or joints of wrists and hands, though they can appear elsewhere. … They are filled with a jelly-like fluid and might arise from inflammation, joint or tendon injury, or unknown causes. … The size can vary, and while many ganglion cysts are painless, if they press on a nerve, they can cause pain, tingling, and muscle weakness. … Treatment is not always necessary, especially if the cyst doesn't cause discomfort. … However, if problemati