Ganglion cysts develop over joints and tendon sheaths. Fluid accumulates inside a small sac which is connected to its surroundings at first, then slowly separates, creating a fully formed cyst.
It is not known why ganglion cysts develop. Trauma to the limb, overexertion, joint wear, inflammation of the tendon sheath can all contribute to the formation of ganglion cysts. They can occur in both men and women, and at any age, but they are most common in women between the ages of 20 and 40.
The size of the cyst may change over time: it can grow, shrink, disappear or reappear, depending on how much the affected limb is used.