Epidemiology

• Can affect all age groups; unusual in children
• Most common in ages 20 to 40 years and 3 times as common in women
• Common in dorsal wrist, radial wrist, and dorsum of the distal interphalangeal (DIP) joint (referred to as a mucous cyst)
• Mucous cysts are usually seen in older patients.
• 60–70% of hand and wrist ganglion cysts are on the dorsal wrist; 15–20% are on the volar wrist.

Prevalence

• Prevalence of wrist ganglia in patients presenting with wrist pain is as high as 19%.
• Prevalence of ganglia in patients with a palpable mass in the wrist is as high as 27%.
• Reported prevalence in ankles is 5.6%.

Etiology and Pathophysiology

Pathogenesis is unclear. Cysts are filled with mucin and communicate with the adjacent joint space, tendon, and/or tendon sheath via a stalk. Several theories about their origin include:

• Herniation of synovial lining creates a one-way valve. Although this is supported by dye studies, the lack of a synovial (epithelial) lining in the cyst wall makes this less likely.
• Mucoid degeneration of connective tissue results in formation of hyaluronic acid, leading to cystic space formation. Studies haven’t confirmed this hypothesis.
• Joint stress leads to a tear in the joint capsule or tendon sheath allowing synovial fluid to leak into surrounding tissues. Local irritation leads to production of fluid and a pseudocapsule forms (explaining the lack of an epithelial lining).
• Recurrent stress may stimulate mucin production by nearby mesenchymal cells (seen on electron microscopy) resulting in cyst formation (1).

Genetics
No specific genetic links have been found.

Risk Factors

• Female > male
• Osteoarthritis for mucoid cysts
• Joint trauma (possible but not proven)

Commonly Associated Conditions

Mucous cysts are usually associated with osteoarthritis at the DIP joint.