Morrant Baker (popliteal) cyst or pseudothrombophlebitis syndrome

Introduction

A cyst in the midline of the popliteal fossa, at or below the femorotibial junction.

Epidemiology

• incidence is 5% (by MRI)
• commonly associated with inflammatory joint disease, especially rheumatoid arthritis

Pathology

• popliteal cysts are connected to the gastrocnemio-semimembranous bursa in the calf
• pressure diverticulum of the synovial sac protruding through the joint capsule of the knee
• may compress the popliteal vessels
• one-way valve effect where fluid may go from the knee to the popliteal synovial bursa, but not in reverse
• cysts may dissect into the calf or rupture

Clinical manifestations

• calf pain & swelling
• knee effusion
• protrudes when the knee is extended & is not visible with flexion, unless very large
• if the communication is patent, gradual steady pressure on the sac forces some fluid back into the joint cavity, temporarily reducing swelling
• swelling may be translucent
• cysts are usually along the medial side distal to the transverse skin crease

Radiology

• duplex ultrasound
  • assessment of popliteal space
  • rules in/out deep vein thrombosis (DVT)
• magnetic resonance imaging
• arthrography is gold standard for diagnosis

Differential diagnosis

• deep vein thrombosis

Management

• no treatment necessary for asymptomatic popliteal cysts
• glucocorticoid injection
• joint aspiration
• ultrasound-guided cyst aspiration with glucocorticoid injection
• bed rest for 48 hours
• elastic wrap when weight-bearing or ambulating to reduce swelling of calf & ankle
• gradient elastic stocking as calf & ankle swelling diminish
• non-steroidal anti-inflammatory agents for pain & inflammation
• surgery

More general terms

• cyst