Synovial Cyst of the extensor digitorum superficialis: A case report

Background: A synovial cyst is a herniation of synovial tissue through a joint capsule, often mistaken for a ganglion cyst. The key distinctions are that synovial cysts have a synovial cell lining, while a ganglion cyst is delineated by dense fibrous connective tissue. Typically found near joints, synovial cysts are associated with conditions like osteoarthritis, prevalent in females aged 20 to 50. We present a rare case of a synovial cyst in the extensor digitorum superficialis of the right hand. Case summary: A 53-year-old Hispanic female visited our hand clinic due to a 3-year history of pain on the back of her right hand. At exploration, a 3 × 3 cm soft tumor was identified. Surgery revealed a clear-yellowish mass within the extensor digitorum superficialis tendon. Following the surgery, synovial cyst was confirmed by pathology and the patient was discharged without complications. Conclusion: This case highlights the rare presentation of an intratendinous synovial cyst and emphasizes the importance of a comprehensive understanding of synovial cysts in the differential diagnosis of hand tumors.