- Epidemiology & Location:
- Most common soft-tissue mass of hand/wrist; peak in young adults (20–40 yo, F > M).
- Most common site: Dorsal wrist (~70%, scapholunate joint); volar wrist (~20%) near radial artery.
- Pathophysiology:
- Fluid-filled pseudocyst (lacks synovial/epithelial lining) containing gelatinous, hyaluronic acid-rich mucin resulting from repetitive microtrauma or joint capsule degeneration.
- Clinical Presentation:
- Smooth, rubbery, mobile, well-circumscribed mass; size fluctuates w/ joint activity.
- Usually painless or presents w/ a dull ache during extreme wrist motion.
- Key physical exam finding: (+) Transillumination (differentiates fluid-filled cyst from solid tumor).
- Diagnosis:
- Clinical: Made via history, exam, and (+) transillumination.
- Ultrasound: Initial imaging if atypical/unclear (reveals anechoic, avascular mass w/ posterior acoustic enhancement).
- X-ray: Normal; performed only to rule out underlying OA, fractures, or bone pathology.
- MRI: Reserved for occult dorsal wrist pain without a palpable mass.
- Key Differentials:
- Giant cell tumor of tendon sheath: Solid mass, does not transilluminate, common on volar digits.
- Epidermoid cyst: Attached to skin, central punctum, cheesy keratin material, does not transilluminate.
- Lipoma: Soft, lobulated, subcutaneous, does not transilluminate.
- Management:
- Asymptomatic (First-line): Observation & reassurance (~50% resolve spontaneously).
- Symptomatic / Impairment (Second-line): Closed needle aspiration (diagnostic/therapeutic; ~50% recurrence rate; avoid blind aspiration on volar side due to radial artery risk).
- Refractory / Recurrent / Nerve Compression (Definitive): Surgical excision (must resect cyst along with pedicle/joint capsule to lower recurrence to 5–15%).