Popliteal (Baker's) Cysts

Key Points

• Fluid-filled synovial cyst in the popliteal fossa
• More common in children aged 4-7 years
• Usually benign and self-limiting in children
• Often associated with underlying joint pathology
• Different etiology and management compared to adult Baker's cysts

Overview

Popliteal cysts, also known as Baker's cysts, are synovial fluid-filled lesions located in the popliteal fossa. In children, they often present as an incidental finding and may be asymptomatic. Unlike adults, pediatric popliteal cysts frequently occur without associated intra-articular pathology.

Pathophysiology

Anatomical Considerations:

• Formation mechanism:
  • Distention of gastrocnemius-semimembranosus bursa
  • Communication with knee joint space
  • One-way valve mechanism
• Associated Conditions:
  • Juvenile Idiopathic Arthritis (JIA)
  • Trauma
  • Synovitis
  • Meniscal tears (rare in children)

Histopathology:

• Synovial lined cavity
• Fibrous wall composition
• Connection to knee joint via semimembranosus bursa

Clinical Presentation

History:

• Often asymptomatic
• Presenting complaints:
  • Posterior knee swelling
  • Mild discomfort with activity
  • Feeling of tightness
  • Occasional pain
• Associated symptoms:
  • Joint stiffness
  • Limited range of motion
  • Activity-related discomfort

Physical Examination:

• Inspection:
  • Visible posterior knee swelling
  • Usually soft and non-tender
  • More prominent with knee extension
• Palpation:
  • Soft, compressible mass
  • Usually non-tender
  • Mobile in transverse plane
• Special Tests:
  • Foucher's sign
  • Transillumination test

Diagnosis & Assessment

Imaging Studies:

• Ultrasound:
  • First-line imaging modality
  • Shows anechoic or hypoechoic mass
  • Can assess for complications
• MRI:
  • Gold standard for evaluation
  • Shows relationship to surrounding structures
  • Identifies associated pathology
  • T2-weighted images show fluid signal
• X-rays:
  • Limited utility
  • May show soft tissue shadow
  • Rules out bony abnormalities

Differential Diagnosis:

• Soft tissue tumors
• Arterial aneurysms
• Deep vein thrombosis
• Ganglia
• Synovial sarcoma

Management

Conservative Treatment:

• Observation:
  • First-line treatment in children
  • Regular monitoring
  • Spontaneous resolution common
• Activity Modification:
  • Avoid aggravating activities
  • Range of motion exercises
  • Physical therapy if needed

Medical Management:

• NSAIDs for symptomatic relief
• Treatment of underlying condition if present
• Aspiration:
  • Rarely indicated in children
  • High recurrence rate

Surgical Management:

• Indications:
  • Large, symptomatic cysts
  • Failed conservative treatment
  • Complications
• Surgical Options:
  • Open excision
  • Arthroscopic treatment
  • Treatment of underlying pathology

Complications & Prognosis

Potential Complications:

• Rupture:
  • Pseudo-thrombophlebitis
  • Compartment syndrome (rare)
• Compression:
  • Neurovascular compromise
  • Deep vein thrombosis (rare)
• Recurrence after treatment

Prognosis:

• Generally excellent in children
• High rate of spontaneous resolution
• Better outcomes compared to adults
• Regular monitoring recommended