A Case Study of Baker Cysts With Intramuscular Extension into the Medial Head of the Gastrocnemius

Abstract

Baker cysts are common pathological findings during sonography of the popliteal fossa. Although they can present as a typical, mild variant or have an atypical sonographic appearance, a common feature of them is that their expansion is usually limited in the intermuscular planes or spaces between muscles and knee capsule. Baker cysts extending into muscles are rare. Two cases of a Baker cyst with extension into the medial head of the gastrocnemius (MHG) are reported with sonographic findings. Both of the cases were discovered in females, who had anterior or bilateral knee pain and radiographic features of osteoarthritis. Knee effusion was identified sonographically in both of the patient cases. In the popliteal fossa, Baker cysts were found in both patients with intramuscular extension into the MHG. In the first case, a cystic penetration was noted into the MHG, near the neck of the cyst, having a cone shape and oriented toward the inferior aspect of the muscle. The second case had a cystic penetration into the MHG near the base of the cyst with a tube shape, along its long axis. The possible pathogenesis is discussed.