Pathogenesis

Pathophysiology

• two types of digital mucoid cyst have been described, based on the origin of the lesion (1)
  • first type is located at the proximal nail fold and usually is not directly confluent with either an interphalangeal joint or underlying tendon sheath
    • cause has been described as that of localized fibroblast proliferation within the dermis (2)
      • there is a consequent increase in hyaluronic acid production that can lead to focal cutaneous mucinosis and resultant cyst formation
    • second type has been described as a lesion on the dorsal lateral aspect of a digit at the distal interphalangeal joint
      • theoretically, these cysts are caused by a herniation of tendon sheaths or joint linings similar to ganglion cysts located elsewhere in the body
        • these cysts have a stalk-like connection with a joint or tendon sheath
        • stalk allows for the transfer of mucin into the cyst
        • recurrence may be secondary to incomplete excision of this stalk

Reference:

• 1) Karte K et al. Acquired clubbing of the great toenail. Digital mucoid cyst (pseudocyst). Arch Dermatol (1996);132:223-228.
• 2) Drape JL et al. MR imaging of digital mucoid cysts. Radiology (1996); 200: 531-536