A ganglion cyst is a non-cancerous, fluid-filled sac that typically develops near a joint or along a tendon sheath. These cysts are relatively common on the foot or ankle, though they are most frequently found around the wrist. The mass is a balloon-like outgrowth filled with synovial fluid, a thick, jelly-like liquid that naturally lubricates joints and tendons. The cyst forms when this fluid collects outside its normal boundaries. Approximately 11% of all ganglion cysts form on the foot or ankle.
Where and Why Ganglion Cysts Form on the Foot
Ganglion cysts can develop virtually anywhere on the foot, but they most commonly appear on the top of the foot, often over the midfoot bones or near the ankle joint. The lateral, or outer, aspect of the ankle is another frequent site.
The precise origin of a ganglion cyst is not fully understood, but the prevailing theory connects their formation to irritation or stress on a joint or tendon. Repeated stress, a single traumatic event, or microscopic tears can weaken the joint capsule or tendon sheath. This weakness allows synovial fluid to leak out and accumulate in a localized sac under the skin.
The foot is susceptible to this type of cyst due to factors like repetitive stress from activities such as running or sports. Tight or ill-fitting footwear can also contribute by causing constant friction or pressure. Underlying joint issues, such as arthritis or bone spurs, can also irritate surrounding tissues, potentially leading to cyst formation.
Recognizing the Signs and Getting a Medical Opinion
The most apparent sign of a ganglion cyst is a noticeable lump beneath the skin, ranging in size from a small pea to a golf ball. This mass may feel soft and spongy or firm and rubbery, and it often fluctuates in size. For many individuals, this visible lump is the only symptom they experience.
If the cyst grows large enough to press on surrounding structures, it can cause secondary symptoms. If situated near a nerve, a person may feel tingling, burning, or numbness, sometimes radiating into the toes. Pain is also a common complaint, usually a dull ache that occurs when the cyst presses against a tendon or joint during movement, or causes discomfort when wearing shoes.
To confirm a diagnosis, a medical professional performs a physical examination, assessing the lump’s texture and mobility. A common diagnostic technique is transillumination, where a light is shined through the mass; the fluid-filled cyst typically allows the light to pass through, unlike a solid tumor.
Imaging studies are also used to provide a definitive diagnosis and rule out other conditions. An ultrasound or Magnetic Resonance Imaging (MRI) scan can clearly show the fluid-filled nature of the mass and its connection to the underlying joint or tendon. These tools are useful for confirming smaller or deeper cysts that are not easily visible. In some cases, a small amount of fluid may be removed for evaluation, a process known as aspiration.
Non-Surgical and Surgical Treatment Options
Treatment for a ganglion cyst depends on whether it is causing symptoms. If the cyst is small, painless, and does not interfere with daily activities, the most common approach is watchful waiting, as these masses can sometimes disappear on their own. Modifying footwear or using padding can also help reduce discomfort for asymptomatic cysts.
For cysts causing pain or limiting movement, medical intervention is recommended. A common, minimally invasive procedure is aspiration, which involves using a needle to drain the fluid from the sac. A steroid medication may be injected following aspiration to help reduce inflammation.
While aspiration provides immediate relief, the cyst has a high rate of recurrence, sometimes as high as 70%. This high recurrence occurs because the stalk connecting the cyst to the joint or tendon sheath is often left behind.
If the cyst is painful, keeps returning after aspiration, or is pressing on a nerve, surgical excision may be necessary. Surgical removal involves excising the entire cyst, including the stalk where it originates. This outpatient procedure provides a lower recurrence rate compared to aspiration. Following surgery, patients may need immobilization with a splint or cast and may require crutches for up to a few weeks to allow the surgical site to heal.