A mucous cyst is a benign, fluid-filled sac that forms as a smooth, rounded lump near joints or within soft tissues, often appearing translucent or skin-colored. These cysts are harmless and non-cancerous. Understanding their origins involves examining the processes that lead to fluid accumulation or tissue changes.
Primary Causes of Mucous Cysts
Mucous cysts arise from disruptions to tissues, leading to fluid collection. Physical trauma or injury is a common factor. Direct impact or repetitive stress can damage tissues, causing fluid to leak from vessels or glands and accumulate in a localized area, forming a cyst.
Chronic inflammation also contributes to cyst development. Persistent inflammatory responses can alter tissue structure and promote fluid retention, creating an environment for cyst formation. This prolonged irritation can lead to changes in cells that produce mucin, causing an excessive buildup.
Degenerative joint disease, such as osteoarthritis, plays a role in some mucous cysts. As cartilage within joints breaks down, it can affect the surrounding soft tissues, leading to fluid leakage from the joint capsule and cyst formation. Synovial fluid, which lubricates joints, can seep out and collect under the skin.
Obstruction or rupture of small ducts or glands is another common cause. When a duct, such as a salivary gland duct, becomes blocked or is damaged, its fluid can become trapped, leading to a swelling that develops into a cyst. This prevents the natural flow of secretions, causing them to back up and form a fluid-filled sac.
Common Locations and Their Specific Causes
Mucous cysts frequently appear in specific anatomical locations, each with distinct contributing factors. Digital mucous cysts, found on fingers and sometimes toes, often connect to underlying osteoarthritis in the distal interphalangeal (DIP) joints (closest to the fingertips). Degeneration of joint cartilage and bone spurs (osteophytes) from osteoarthritis can cause synovial fluid to escape and collect near the nail fold or joint, forming these cysts. While osteoarthritis is the most common link, trauma or repetitive motion can also contribute, especially in younger individuals.
Oral mucous cysts, known as mucoceles or ranulas, form on the lips, cheeks, or floor of the mouth. Mucoceles, typically on the lower lip, result from trauma like biting the lip or cheek, which can rupture or obstruct a minor salivary gland duct. This causes saliva to leak into the surrounding tissues, forming a fluid-filled sac. Ranulas, on the floor of the mouth, are larger and develop due to the obstruction of larger salivary glands, such as the sublingual gland.
Nasal and sinus mucous cysts, also called sinonasal mucoceles, develop within the nasal cavity or paranasal sinuses. These cysts are caused by mucus buildup within sinus drainage channels. Obstruction can result from chronic inflammation due to sinusitis, allergies, or infections. Nasal polyps, bony tumors, or complications from previous sinus surgeries can also block these pathways, leading to mucus accumulation and cyst formation.
Recognizing the Signs of a Mucous Cyst
Identifying a mucous cyst involves observing its visual and tactile characteristics. These cysts present as smooth, rounded, and sometimes dome-shaped bumps. Their color varies, appearing translucent, skin-colored, reddish, or bluish, and they often have a pearly or semi-clear surface.
When touched, a mucous cyst feels soft and fluid-filled, or sometimes firm and rubbery. Sizes range from a few millimeters to about 1 centimeter, though ranulas in the mouth can be larger, reaching several centimeters. While many are painless, some may cause discomfort or pain, particularly if pressure is applied or if they grow large enough to affect surrounding structures. Digital mucous cysts can cause a groove or deformity in the nail if they press on the nail matrix.
When to Seek Professional Advice
Consulting a healthcare professional is advised if a mucous cyst causes symptoms or concerns. If the cyst becomes painful, grows rapidly, or interferes with normal functions such as chewing, speaking, or joint movement, medical evaluation is needed.
Signs of infection, such as increased redness, warmth, swelling, or the presence of pus, also indicate a need for medical attention. A healthcare provider can provide an accurate diagnosis, differentiate the cyst from other conditions, and discuss management options if the cyst is bothersome or problematic.