A 42-year-old woman comes to the office for evaluation of a mass at her right wrist. The patient first noticed swelling in her wrist a few months ago after spending a week knitting blankets for her family. The mass has not caused any pain or stopped her from participating in daily activities, but it continues to slowly increase in size. Medical conditions include hyperlipidemia and rheumatoid arthritis. Medications include methotrexate, a statin, and occasional ibuprofen. Vital signs are normal. BMI is 28 kg/m². There is slight ulnar deviation at both wrists, with a 2-cm mass on the extensor surface of the right wrist and no overlying skin discoloration. The mass is firm, mobile, and nontender to palpation, and it transilluminates on penlight examination. Which of the following is the most likely diagnosis in this patient?

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11ec25c8_d86d_476b_bc81_657aa6b7c0c9_MD0003_00 This patient, with a mobile, nontender swelling at the dorsal surface of the wrist, has a ganglion cyst. Ganglion cysts are generally harmless lesions that are most common in patients with underlying joint disorders or prior joint injury. They can occur in both upper and lower extremities but are most common at the wrist. Ganglion cysts are typically filled with mucinous fluid and often communicate with the underlying joint via a hollow pedicle; fluid is postulated to flow from the joint space to the cyst, and a one-way valve mechanism prevents return flow to the joint. The diagnosis of ganglion cyst is usually obvious on inspection and can be confirmed on transillumination of the mass. If in doubt, ultrasound or MRI can confirm the diagnosis, but imaging is rarely necessary. Most ganglion cysts resolve spontaneously and require no treatment. For the few patients with painful and persistent symptoms, options include aspiration and surgical excision. (Choices A, C, and D) Epidermoid cysts are small (<1 cm), freely mobile nodules, typically with a central punctum; they develop most commonly on the palmar surface of the digits. Lipomas are soft, fleshy masses found in subcutaneous tissues; they are usually on the trunk or shoulders. Rheumatoid nodules are firm, fibrotic masses typically found in subcutaneous tissues overlying pressure points (eg, olecranon, dorsal forearm). Unlike ganglion cysts, these lesions do not transilluminate. Epidermoid cysts Lipomas Rheumatoid nodules (Choice E) Tendinous xanthomas are smooth, firm growths that are most commonly seen in patients with severe hyperlipidemia or lipid storage disorders. They are typically multifocal (most common on the Achilles tendon), move with the tendon, and do not transilluminate. Educational objective: Ganglion cysts are mobile, nontender swellings that occur most commonly at the dorsal surface of the wrist. The diagnosis is usually obvious on inspection and can be confirmed on transillumination of the mass. Most ganglion cysts resolve spontaneously and require no treatment. References: Ganglion cyst. (http://www.ncbi.nlm.nih.gov/pubmed/29262133)

A 42-Year-Old Woman Comes to the Office for Evaluation of a Mass