Atypical Calf Cyst Treated With Doxycycline Sclerotherapy

Abstract There are many types of cysts in the leg; the most common is a popliteal (Baker’s) cyst. This occurs when synovial fluid fills the tissue plane between the medial head of the gastrocnemius and the semimembranosus muscle and is often associated with intraarticular knee pathology. Treatment for various types of cysts includes aspiration with or without fenestration, injections with corticosteroids, dextrose, or various sclerosing agents, and surgical excision. This case describes a 58-year-old man with a large cyst measuring 14.7x2.7x3.1 cm in size in the lateral calf, within the lateral gastrocnemius, with atypical size and location for a calf cyst. CT arthrogram showed intraarticular communication with the knee. The cyst recurred after two aspirations and injections with 25% dextrose/lidocaine. Aspiration and injection with doxycycline resulted in temporary relief followed by recurrence. Complete cyst resolution occurred after final aspiration without injectate. The cyst was likely synovial based on location, intraarticular communication, and fluid analysis. We suspect that complete resolution may have been due to repeated aspiration and injection, essentially performing longitudinal cyst fenestration, with possible contribution from doxycycline injection. Further study of intra-cyst doxycycline injection with re-aspiration after 10 minutes for treatment of refractory cysts may be warranted.