A Cystic Mass in the Popliteal Fossa and Its Differential Diagnosis

Im ag es A cystic mass arising in the popliteal fossa can be either a meniscal cyst, a synovial cyst (Baker’s cyst), or a ganglionic cyst [1]. Soft-tissue popliteal masses can be evaluated using physical examinations and imaging studies, such as computed tomography (CT) or magnetic resonance imaging (MRI). Thereafter, pathologic studies can be used for making a final confirmation of the diagnosis. Ganglionic cysts are soft-tissue masses caused by the myxoid degeneration of the connective tissue at the joint capsules and tendon sheaths. They are filled with a gel-like material lined with a flat spindle cell membrane. They are common around the wrist or the foot joint. When found in the popliteal fossa, they are mostly intra-articular cysts connected with the knee joint space and can rarely be intramuscular cysts [2]. Therefore, surgeons may mistake ganglionic cysts in the popliteal fossa for Baker’s cysts or meniscal cysts. A 47-year-old woman presented to our hospital with an 8-month history of a left calf mass in the popliteal fossa. She reported an increase in size and pain at palpation. She had no history of trauma or systemic diseases. Upon physical examination, we found a firm and fixed mass, measuring about 5 cm × 3 cm, over the popliteal fossa. She had a full range of motion of the knee joint and no symptoms. Preoperative CT revealed a lobulated cystic mass measuring 5 cm × 3 cm in the proximal part of the lateral head of the gastrocnemius muscle. It was not connected within the knee joint space (Fig. 1). The mass appeared to be an intramuscular ganglionic cyst or an old hematoma; however, we were not able to rule out Baker’s cyst due to the location. Upon exploration, we opened the muscle sheath and found the mass located in the fiber of the gastrocnemius muscle. Being careful not to damage the lateral and medial sural nerve, we dissected the muscle and soft tissues around the mass and found no connection within the knee joint. Then, we