Ganglion cysts are the most frequent type of hand tumor or lump. They are not malignant and, in most circumstances, are not harmful. They can appear in a variety of areas, but the most common is on the back of the wrist. These fluid-filled cysts can emerge, vanish, and change size fast. They are not caused by injury nor do they represent bone cancer. Cysts can be simple or complex. A ganglion is a simple cyst that does not contain any tissue other than fluid. Ganglia usually do not cause problems until they reach a large size because the increased pressure inside the cyst may force some material out through tiny openings in its surface. This material may look like dust or sand when it escapes and collect below the skin's surface. Complex ganglia contain tissues similar to those found in normal joints such as muscle, tendon, and ligament. Because of this similarity, complex ganglia are also called synovial cysts. Unlike simple ganglia, which always remain under the skin's surface, synovial cysts may protrude through the skin or be embedded within it. Computed tomography (CT) or magnetic resonance imaging (MRI) can help diagnose and determine the size of these tumors. Synovial cysts often arise from one of the tendons in the hand near where it attaches to the bone.