Definition and Diagnosis
Fluid filled cysts that have a synovial membrane. Synovium is what lines joints throughout the body. Synovial cysts commonly communicate with nearby joints and may enlarge when joint pressure increases with movement or weight bearing. Synovial cysts may compress nerves causing pain radiating down a limb, numbness, and weakness. Sometimes these cysts may invade a nerve and damage it from within; an example of this would be the peroneal nerve at the knee, or the suprascapular nerve in the shoulder. Diagnosis is confirmed with MRI, where a cystic lesion is seen compressing or expanding the symptomatic nerve. Electrical testing can help guide treatment. Synovial cysts occur with osteoarthritis, rheumatoid arthritis, and repetitive trauma.
Coronal MRI of the knee (view from behind) revealing a synovial cyst within the common peroneal nerve (arrowheads)
Treatment Options
Asymptomatic synovial cysts are not treated. If progressive or persistent nerve pain, numbness, or weakness is present, especially if there is electrical evidence of nerve damage, these cysts should be drained and removed with surgery. Although surgery is usually efficacious, cyst recurrence can occur. Complications from surgery are rare, but include weakness and possible fluid collection in the wound.
Further Reading
National Institute of Neurological Disorders and Stroke
Repetitive Motion Disorders Information Page
