Ganglion of the wrist is the number one soft tissue hand mass. If a mass is present in the wrist, there is a 70% probability that it is a ganglion.
The bump or the cyst is filled with gelatinous material that can change in size and is close to a tendon sheath or the wrist joint. The causes of cysts are unknown. It may be caused by trauma or degeneration and weakness of the capsule.
Ganglion cysts of the wrist can be either dorsal or volar. A ganglion cyst that grows on the top of the wrist is called a dorsal ganglion. Dorsal ganglion is common (70%) and arises from the scapholunate ligament. A ganglion cyst that grows on the bottom of the wrist is called a volar ganglion. These are less common (20%), but are most common between the Flexor Carpi Radialis (FCR) and Abductor Pollicis Longus (APL) muscles. Volar cysts arise from the radiocarpal joint or the STT joint.
For a dorsal cyst, the bump or the mass is well defined, localized, smooth and not attached to the underlying skin. The mass will be translucent. The mass is obvious with flexion of the wrist, so an MRI is not needed. A volar cyst may be diagnosed with an MRI; however, ultrasound imaging is better for showing the relationship between the artery and the ganglion.
Dr. Nabil Ebraheim's Blog 