What is the likely diagnosis for a patient with well-defined anechoic to hypochoic cystic lesions in both popliteal fossae?

Baker's Cyst (Popliteal Cyst)

The bilateral well-defined anechoic to hypochoic cystic lesions located between the medial heads of the gastrocnemius muscles and the semimembranosus tendons are diagnostic of Baker's cysts. 1

Diagnostic Confirmation

The anatomic location and ultrasound characteristics are pathognomonic for Baker's cysts:

• Baker's cysts characteristically appear as comma-shaped extensions visualized sonographically between the medial head of gastrocnemius and semimembranosus tendon 1, 2
• The anechoic to hypochoic appearance with posterior acoustic enhancement confirms fluid-filled cystic structures 1
• Absence of internal septations or solid components indicates simple cysts rather than complex lesions 1
• Baker's cysts are fluid accumulations in the bursa of the gastrocnemius or semimembranosus muscles that frequently communicate with the knee joint space 1, 2

The bilateral presentation (right: 2.13 cm x 0.62 cm; left: 1.15 cm x 0.43 cm) is not uncommon, as 5% to 32% of knee problems may have these cysts depending on the population studied 3

Clinical Context and Underlying Pathology

In adult patients, Baker's cysts typically indicate underlying intra-articular knee pathology:

• Degenerative joint disease (osteoarthritis) is the most common associated condition 4, 3
• Inflammatory arthropathies including rheumatoid arthritis 5
• Meniscal tears or other internal derangements 4
• The cysts arise from a valvelike mechanism allowing one-way passage of synovial fluid from the joint into the gastrocnemio-semimembranosus bursa, causing distention 3

Plain radiographs of the knee (anteroposterior, lateral, sunrise/Merchant, and tunnel views) should be obtained first to evaluate for underlying joint pathology causing the cyst 1

Important Differential Diagnosis

Critical pitfall: Do not assume all popliteal masses are benign Baker's cysts 1

The following must be excluded:

• Popliteal artery aneurysm—especially in patients with history of other arterial aneurysms or atherosclerotic disease 1, 5
• Deep vein thrombosis (DVT)—particularly if the cyst ruptures, as ruptured Baker's cysts clinically mimic DVT with sudden calf pain, swelling, and inflammation 1, 2
• Soft tissue tumors or masses 4
• Thrombosed popliteal vein 5

Ultrasound with Doppler can simultaneously evaluate for both Baker's cyst and DVT, and can determine vascularity to exclude popliteal artery aneurysm 1

Management Approach

Asymptomatic or Minimally Symptomatic Cysts

Asymptomatic cysts found incidentally require no treatment 3

Symptomatic Cysts—Address the Underlying Knee Pathology

Treatment must focus on the underlying knee condition, not the cyst itself:

• Topical NSAIDs are the preferable first-line pharmacologic therapy due to superior safety profile and should be considered before oral NSAIDs 2
• Oral NSAIDs should be used at the lowest effective dose for the shortest duration, with monitoring for gastrointestinal, cardiovascular, and renal adverse effects 2
• Intra-articular corticosteroid injection into the knee joint is strongly recommended, demonstrating short-term efficacy by reducing both knee joint inflammation and Baker's cyst size 2
• Self-management education programs and activity modifications for osteoarthritis-related cysts 2
• Weight management for overweight patients 2
• Physical therapy to strengthen surrounding muscles 2

Interventional Options for Persistent Symptoms

Ultrasound-guided aspiration may provide temporary relief for symptomatic cysts, and corticosteroid injection into the knee joint may be beneficial when there is associated synovitis 1

However, simple aspiration without sclerotherapy or corticosteroid injection invariably results in cyst refilling and should not be considered definitive therapy 2

Surgical Excision

Surgical excision is rarely necessary and should be reserved for cases that fail conservative management 3

Arthroscopic surgery should be avoided for degenerative knee disease associated with Baker's cysts, as evidence shows no benefit over conservative management 1

Medications to Avoid

• Glucosamine is strongly recommended against, as studies with lowest risk of bias fail to show important benefit 2
• Acetaminophen has very limited utility with small effect sizes and should only be considered for short-term use when NSAIDs are contraindicated, requiring monitoring for hepatotoxicity if used regularly 2

Monitoring for Complications

Watch for cyst rupture, which presents with:

• Sudden calf pain and swelling mimicking DVT 1, 2
• Dissemination of fluid into the calf 1, 2
• Rarely, compartment syndrome or infection 6

If rupture is suspected, ultrasound is the first-line imaging to evaluate for both ruptured cyst and DVT simultaneously 1