Hematogenous osteomyelitis

Tumor biology and incidence

• Most common in children, with two age peaks: children less than age 2 and children between ages 8 and 10 
• Blood flow through metaphyseal bone slows in growing bones of children, allowing for more turbulent flow and decreased phagocytosis; predispose to infection
• Staphylococcus aureus most common infecting organism

Presentation and physical findings

• In early stages, may not present with systemic signs
• In chronic form, patients may present with history of pain of several months’ duration.
• Blood work
  • Normal to elevated white blood cell count
  • Elevated erythrocyte sedimentation rate (ESR); usually takes 3-5 days to reach its peak
  • Elevated C-reactive protein; reaches peak by day 2 postinfection; more accurate than ESR for monitoring progress of treatment.

Radiographic appearance

Within 24 hours of infection

• Evidence of osteomyelitis
• Soft tissue swelling, loss of definition between fascial planes

Within 7-10 days of infection

• Destructive lytic lesion may be present
• Lesion positive on bone scan

Within 2-6 weeks of infection

• Progressive bony destruction of cortical and medullary bone
• Endosteal sclerosis and periosteal reaction are usually present.

Within 6-8 weeks of infection

• Sequestra, indicating areas of necrotic bone
• May be surrounded by a dense involucrum (periosteal new bone formation)

Nuclear medicine

Children

• Technetium 99m diphosphinate bone scan indicated in most cases
  • False negatives increased if performed in first 24 hours after infection
  • False positves seen with trauma and tumor

Adults

• Sequential technetium-gallium excellent at finding vertebral osteomyelitis
• Indium-labelled leukocyte scan more accurate for detecting subclinical osteomyelitis

MRI

Superior to indium-labelled leukocyte scan in defining extent of infection

Differential diagnosis

• In acute stage, eosinophilic granuloma and Ewing sarcoma
• Can simulate many conditions

Pathology

• Reactive inflammatory cell infiltrate (lymphocytes and plasma cells)
• Neutrophils generally not present
• Mixed cellular infiltrate usually indicates a benign diagnosis
• Necrotic bone and marrow fibrosis also present

Diagnosis and treatment

• Individualize to specific case
• All patients will require antibiotics, with or without surgical debridement

Associated condition: Brodie’s abscess

• Form of chronic osteomyelitis usually seen in lower extremities of young adults
• Often insidious bone infection; usually localized to metaphysis of tibia or femur
• Usually has elongated shape and well-demarcated margin; surrounded by reactive sclerotic bone
• May see radiolucent tract extending away from lesion into growth plate
• Sequestra usually absent