Ganglion cysts form when connective tissue near a joint or tendon breaks down and creates a fluid-filled pocket. Despite decades of study, the exact trigger for this tissue breakdown isn’t fully understood, but several well-established factors make it more likely. These soft, round lumps are the most common type of mass found in the hand and wrist, and they’re not cancerous.
How a Ganglion Cyst Forms
The most widely accepted explanation is that the connective tissue surrounding a joint or tendon sheath undergoes a process called mucoid degeneration. Essentially, the collagen fibers in this tissue start to break down, and small pockets form within the damaged area. These pockets fill with a thick, jelly-like fluid similar to the lubricating fluid inside your joints. Over time, the pockets can merge into a larger cyst that pushes outward as a visible bump under the skin.
Older theories described ganglion cysts as a pouch of joint lining (synovium) that balloons outward, almost like a hernia. But when pathologists examine the cyst wall under a microscope, there’s no cell lining inside it. A true cyst has an inner lining of cells; a ganglion does not. This means it’s not a bubble of joint tissue that popped outward. It’s a new space created by degenerating tissue that then fills with fluid. Some cysts have a narrow stalk connecting them back to the joint capsule, while others appear to sustain themselves independently once formed.
Known Risk Factors
No single cause has been pinpointed, but certain patterns show up consistently in people who develop ganglion cysts.
- Previous joint or tendon injury. A sprain, fracture, or repetitive strain injury like tendonitis can damage the connective tissue around a joint, potentially setting the stage for cyst formation later. Some researchers believe the injury weakens the tissue enough that small areas begin to degenerate and fill with fluid.
- Osteoarthritis. Wear-and-tear arthritis in the hand is strongly linked to ganglion cysts, especially in the finger joints closest to the nails. The bone spurs and joint changes that come with arthritis appear to drive the tissue breakdown that produces cysts in these locations.
- Age and sex. Ganglion cysts are most common in adults between 20 and 50, and they occur more frequently in women than men. The reasons for this aren’t entirely clear, though hormonal and anatomical differences likely play a role.
- Repetitive wrist use. Occupations or activities that involve repeated wrist motion may increase the likelihood, though the evidence here is less definitive than for injury or arthritis.
Where They Appear Most Often
About 70% of wrist ganglion cysts grow on the back of the wrist (the dorsal side), typically originating from the ligament between two small wrist bones. Roughly 20 to 25% develop on the palm side (the volar side), usually arising from a different set of wrist joints. A small percentage appear on the sides of the wrist or along the tendons in the fingers and palm.
The location matters because it hints at the underlying source. Dorsal wrist ganglions tend to arise from ligaments under mechanical stress during normal wrist movement. Volar ganglions sit closer to the radial artery, which is one reason doctors take extra care when evaluating lumps on the palm side of the wrist.
Finger Cysts and Arthritis
Ganglion cysts that appear near the fingertip, right behind the nail, deserve their own mention. These are sometimes called mucous cysts, and they’re closely tied to osteoarthritis in the last finger joint. X-rays of affected fingers almost always show bone spurs and joint narrowing at the same site. Studies have found that arthritis tends to be more severe in fingers with these cysts compared to unaffected fingers on the same hand.
A narrow stalk often connects the cyst back to the arthritic joint capsule. This connection is so important that in one study, surgeons who removed only the bone spurs (without excising the cyst itself) saw the cyst regress on its own in nearly every case. This strongly suggests that the arthritic changes in the joint are driving the cyst formation, not the other way around.
What Doesn’t Cause Them
Ganglion cysts are not tumors and are not caused by infection or cancer. They contain no abnormal cells. The fluid inside is simply a thick mucin, similar in composition to normal joint fluid but more concentrated. There’s also no evidence that cracking your knuckles, typing, or any single everyday habit directly causes them, though sustained repetitive stress on a joint could contribute over time.
Do They Go Away on Their Own?
Many do. Guidelines from the British Society of Surgery for the Hand note that roughly 55% of untreated ganglion cysts resolve spontaneously within six years. For cysts that aren’t painful and don’t interfere with hand function, observation alone is a reasonable approach.
When a cyst is bothersome, the two main options are aspiration (draining the fluid with a needle) and surgical removal. Aspiration is quick and minimally invasive, but the recurrence rate is high, ranging from about 50 to 80% depending on the study. Surgical excision has a much lower recurrence rate, generally between 13 and 28%, because the surgeon removes the cyst wall and its connection to the underlying joint or tendon sheath. Even after surgery, though, recurrence is possible if the tissue degeneration that created the cyst continues.
How They’re Identified
Most ganglion cysts are diagnosed by physical exam alone. They feel firm but slightly spongy, move a little under the skin, and are usually painless unless they press on a nerve. One classic test involves shining a light through the lump. Because the cyst is filled with clear, jelly-like fluid rather than solid tissue, light passes through it. A solid mass would block the light. If there’s any uncertainty, an ultrasound or MRI can confirm the diagnosis and reveal whether the cyst connects to a joint or tendon sheath beneath it.