Synonyms

• Unicameral Bone cyst
• UBC

Category

Bone

Behaviour

Benign

Gender

Both equally

Tissue of Origin

Bone

Epidemiology

• Most common Bone cyst in children
• Peak incidence in children <20 years
• Predilection for metaphysis of long Bones adjacent to growth plate
• Distal femur and proximal humerus most common

Clinical Features

• Usually asymptomatic
• Incidental finding
• Pathological fracture if large

Location

• Distal femur (most common)
• Proximal humerus
• Proximal femur
• Pelvis
• Tibia

Imaging

• Plain radiograph: central radiolucent lesion with sclerotic margin
• Falling fragment sign (pathognomonic if present)
• MRI: simple cyst with no internal septation

Pathology

• Simple cyst with clear fluid
• Fibrous membrane wall
• No endothelial lining

Genetics

Sporadic

Treatment

• Observation: many regress spontaneously with skeletal maturity
• Intralesional injection: methylene blue, OK-432, or Bone marrow
• Curettage and Bone graft if symptomatic or fracture

Prognosis

• Excellent: often involute spontaneously
• May persist into adulthood

Key Points

• Benign self-limited lesion
• Observation appropriate initially
• Multiple effective injection treatments

Workup - Blood Tests

No tests required

Workup - Local Imaging

• Plain radiograph: falling fragment sign pathognomonic
• MRI if diagnostic uncertainty

Workup - Biopsy

Not required

Workup - Staging

Not applicable