What are the radiological findings suggestive of fat embolism syndrome?

Radiological Findings in Fat Embolism Syndrome

The most characteristic radiological findings of fat embolism syndrome (FES) include diffuse, well-demarcated ground-glass opacities and ill-defined centrilobular nodules on chest CT, while brain MRI typically shows distinctive scattered high-intensity lesions in a "starfield" pattern. 1

Chest Imaging Findings

Chest Radiography

• Often normal or non-specific in early stages
• Common findings include:
  • Focal infiltrates
  • Segmental pleural effusions
  • Raised diaphragm
  • Diffuse bilateral pulmonary opacities developing 12-36 hours after injury 2, 3
• A normal chest radiograph in an acutely breathless hypoxic patient with appropriate clinical context (long bone fracture) increases the likelihood of FES 2

Chest CT Findings

• Most sensitive imaging modality for pulmonary manifestations of FES
• Characteristic findings include:
  • Diffuse, well-demarcated ground-glass opacities
  • Ill-defined centrilobular nodules
  • Patchy distribution throughout both lungs
  • Interlobular septal thickening 1
• These findings typically appear within 24-72 hours after the inciting event 3

Brain Imaging Findings

Brain MRI Findings

• Most sensitive modality for neurological manifestations of FES
• Characteristic findings include:
  • Multiple scattered high-intensity lesions on T2-weighted and FLAIR sequences
  • "Starfield pattern" of multiple small, scattered hyperintense lesions
  • Lesions predominantly in white matter, particularly at gray-white matter junctions
  • Diffusion-weighted imaging (DWI) shows restricted diffusion in acute phase 4, 5
• These findings may be present even in patients with predominantly neurological symptoms without respiratory involvement 5

Timing and Evolution of Radiological Findings

• Radiological abnormalities typically develop 12-36 hours after the inciting event (fracture, trauma, orthopedic procedure) 3
• Chest imaging findings may precede clinical symptoms
• Imaging findings usually resolve within 1-4 weeks with appropriate treatment 1

Clinical Context for Interpretation

Radiological findings should be interpreted in the appropriate clinical context:

• Recent history of long bone fracture, pelvic fracture, or orthopedic procedure
• Classic triad of respiratory distress, neurological symptoms, and petechial rash 3, 4
• Onset of symptoms typically 24-72 hours after injury 3

Diagnostic Pitfalls

• Chest radiograph may be normal in early stages despite significant clinical symptoms
• CT findings may mimic other conditions like pulmonary edema or ARDS
• Brain MRI findings may be confused with other embolic phenomena or diffuse axonal injury
• Absence of radiological findings does not exclude the diagnosis if clinical suspicion is high 4, 6

Monitoring and Follow-up Imaging

• Serial chest imaging is useful to monitor disease progression and response to treatment
• Follow-up brain MRI may show resolution of lesions in patients who recover 4
• Continuous monitoring of respiratory status with pulse oximetry and arterial blood gases is essential in managing patients with suspected FES 3