Popliteal cyst is a soft-tissue swelling in the posterior aspect of the knee which contains gelatinous fluid.It is also called Baker Cyst named after Dr. William Morrant Baker who first described it. Most common location is distal the popliteal crease under the medial head of the gastrocnemius muscle.
These conditions have also been referred in the past as gastrocnemio-semimembranosus bursae, semimembranosus burse, synovial cysts, posterior herniae of the knee joint.
The condition is unilateral mostly. It is almost twice as common in boys than the girls.
Pathological Findings
The cysts may be either bursal or hernial in origin. The bursal cysts develops in bursa of the gastrocnemius-semimembranosus bursae. Hernial cysts protrude the capsule to lie outside.
The cysts are medially located mostly but rarely they are laterally located and occasionally extend into the calf of the leg.
Infiltration by lymphocytes, plasma cells, histiocytes, and even polymorphonuclear cells may be seen in varying degrees. Areas of metaplasia into cartilaginous and osteoid elements may also be there.
Clinical Presentation
Symptoms
- Presence of a swelling in the posterior aspect of the knee is the presenting complaint.
- On occasion there may be stiffness and local pain.
Examination
- A swelling is located distal to the popliteal crease
- Swellingbecomes prominent when the knee is hyperextended and disappears on flexion
- Consistency varies from soft to firm
- Transillumination* test is positive
*The passing of a strong beam of light through a part of the body for medical inspection
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