Intraoperative Findings of a Baker’s Cyst

Patient Presentation

A 54-year-old woman presented with gradually progressive pain and a sensation of fullness in the left knee accompanied by visible posterior knee swelling, exacerbated by walking and knee flexion. She denied a history of trauma or inflammatory joint disease but reported having undergone surgical excision for a similar condition affecting the contralateral knee several years earlier. Physical examination revealed a soft, fluctuant, mobile mass measuring approximately 4 × 4 cm in the left popliteal fossa, with variation in size during knee movement; the lesion was non-tender, without calf edema, and distal neurovascular status was intact. In the absence of red flag features, preoperative imaging was deferred. Surgical excision was performed, and the intraoperative image demonstrated a well-circumscribed cystic lesion arising from the popliteal fossa (figure 1). The patient recovered without immediate postoperative complications.

Figure 1.Intraoperative view demonstrating a well circumscribed cystic lesion arising from the popliteal fossa consistent with a Baker’s cyst.

Diagnosis

Left Baker’s cyst (popliteal cyst).

Discussion

Baker’s cyst is a benign synovial fluid-filled distension of the gastrocnemio-semimembranosus bursa that presents as a posterior knee mass.¹ Clinical features commonly include pain, tightness, or a sensation of fullness, with a palpable mass in the popliteal fossa that may fluctuate with knee flexion and extension.

Diagnosis is often clinical in patients with characteristic findings.¹ Important differential diagnoses include deep vein thrombosis, popliteal artery aneurysm, soft-tissue tumors, and abscesses.^1,2 Complicated or ruptured Baker’s cysts have been reported to mimic deep vein thrombosis, posing a diagnostic challenge in patients with posterior knee or calf swelling.³ Imaging with ultrasonography or magnetic resonance imaging is recommended when diagnostic uncertainty or red flag features are present, including a pulsatile mass, rapidly enlarging swelling, calf edema, or neurovascular compromise.² In patients with a typical presentation and intact distal neurovascular examination, imaging may be deferred.

Baker’s cysts are most frequently observed in middle-aged and older adults and are often associated with underlying knee pathology, although they may occur without clinically evident joint disease.¹ Management ranges from observation to surgical excision in symptomatic or persistent cases.² This image highlights the characteristic intraoperative appearance of a Baker’s cyst and reinforces the importance of clinical recognition and risk stratification in patients presenting with posterior knee swelling.