Baker's Cyst and Cancer Risk: What You Need to Know

A Baker's cyst (popliteal cyst) is a fluid-filled swelling behind the knee, usually communicating with the knee joint via a valvular opening. It is almost always benign and secondary to intra-articular pathology:

• Osteoarthritis (most common).
• Meniscus tear.
• Rheumatoid arthritis.
• ACL tear.

Cancer Association

In <1% of cases, a popliteal cyst in the setting of osteoarthritis may be associated with an underlying neoplastic or pre-neoplastic process within the joint (e.g., synovial sarcoma, pigmented villonodular synovitis, metastatic disease). This is exceedingly rare.

When to Investigate Further

• Rapidly enlarging cyst.
• Fixed, hard, or irregular mass.
• Night pain, weight loss, constitutional symptoms.
• Atypical imaging features (solid components, invasion).

Routine cysts are managed by treating the underlying knee condition. Aspiration/injection or excision rarely needed.