A mucous cyst is a common, benign, fluid-filled growth that develops in soft tissues. These sacs are generally painless but can become troublesome depending on their size and location. The two main types are digital mucous cysts (on fingers and toes) and mucoceles (in the mouth and on the lips).
What Exactly Is a Mucous Cyst?
A mucous cyst is a non-cancerous, fluid-filled sac that forms due to a disruption in the normal flow of mucus or joint fluid. The fluid inside is typically thick, clear, and gelatinous, consisting of mucin, a protein found in mucus and synovial fluid. The cyst usually appears as a smooth, dome-shaped lump that may be pearly, translucent, or slightly bluish-pink.
The term “mucous cyst” encompasses two distinct types based on location and cause. A mucocele, or oral mucous cyst, typically occurs on the inner surface of the lower lip but can appear elsewhere in the mouth. Mucoceles form when a minor salivary gland duct is damaged, often by minor trauma like lip biting, causing mucus to leak into the surrounding soft tissue.
Digital mucous cysts appear as firm sacs near the joints of the fingers or toes, most commonly near the last joint of the finger (the distal interphalangeal joint). These growths often connect to the joint space and are associated with underlying joint degeneration, such as osteoarthritis. They can also press on the nail matrix, leading to a groove or deformity in the fingernail.
Expected Duration and Natural Resolution
The question of how long a mucous cyst will last has a variable answer that depends heavily on the cyst’s type and location. Oral mucoceles, which result from trauma to a salivary duct, often have a good prognosis for spontaneous healing. Many small mucoceles will burst on their own, drain, and resolve within a timeframe of three to six weeks.
A conservative approach, such as avoiding habits like lip biting that can traumatize the area, is recommended. While some mucoceles resolve spontaneously after an average of three months, persistence of the underlying trauma can cause the mucocele to last two months or longer.
Digital mucous cysts, which are often linked to underlying joint issues like osteoarthritis, are significantly less likely to resolve naturally. Since the fluid originates from a continually producing joint, the sac tends to refill. These cysts can wax and wane in size, sometimes discharging a sticky fluid, but they frequently persist for many months or even years without intervention.
Monitoring a digital cyst is appropriate only if it is not causing pain or affecting the nail structure. If the cyst presses on the nail bed, it can cause an irreversible groove or deformity. Early treatment may be necessary to prevent permanent nail damage, as smaller cysts with less joint involvement have a better chance for natural resolution.
When Medical Treatment Becomes Necessary
Medical intervention is considered when a mucous cyst causes pain, interferes with function, leads to cosmetic deformity, or fails to resolve naturally after a prolonged observation period. For oral mucoceles, consult a provider if the lesion persists beyond two months, grows larger, or causes difficulty with eating or speaking. For digital cysts, severe pain or a noticeable fingernail deformity are reasons to seek treatment.
Simple aspiration, where fluid is drained with a needle, is a minimally invasive option, but it often results in recurrence because the underlying cause is not removed. Cryotherapy (freezing the cyst) and laser treatment are other less invasive methods used, particularly for mucoceles.
Surgical excision is often the most definitive treatment, especially for digital mucous cysts. For digital cysts, surgery involves removing the cyst sac and its stalk, often addressing underlying bone spurs or joint degeneration (osteophytes). For mucoceles, surgical removal may include the adjacent, damaged minor salivary gland to minimize the chance of the cyst returning.
Addressing Cyst Recurrence
Recurrence is a common issue. For digital mucous cysts, the pathology is often chronic joint inflammation or osteoarthritis, meaning the joint may continue to leak fluid after the cyst is removed. Recurrence rates can be as high as 40% with less invasive techniques like aspiration or steroid injection.
To minimize recurrence, the most effective approach for digital cysts is surgical excision that includes the complete removal of the cyst and any associated osteophytes. For oral mucoceles, recurrence is a concern if the damaged salivary gland is not removed during the procedure. Protecting the affected area from repeated trauma, such as avoiding lip biting, also helps prevent new or recurring mucoceles.