What are the MRI brain findings in fat embolism syndrome (FES)?

MRI Brain Findings in Fat Embolism Syndrome

The characteristic MRI findings in fat embolism syndrome (FES) include multiple small, scattered, non-confluent hyperintense lesions on T2-weighted and FLAIR sequences in a "starfield" pattern, predominantly affecting white matter, with associated diffusion abnormalities that typically represent vasogenic rather than cytotoxic edema. 1, 2, 3

Key MRI Sequence Findings

T2-weighted and FLAIR Imaging

• Multiple small (2-15mm) hyperintense lesions scattered throughout cerebral white matter
• Predominantly bilateral and symmetric distribution
• Lesions typically involve:
  • Subcortical and deep white matter
  • Centrum semiovale
  • Corpus callosum
  • Cerebellum
  • Less commonly basal ganglia and thalami 4, 3

Diffusion-Weighted Imaging (DWI)

• Hyperintense lesions on DWI
• Unlike ischemic stroke, these lesions typically show increased ADC values (not restricted diffusion)
• This pattern suggests vasogenic edema rather than cytotoxic edema 2, 3

Susceptibility-Weighted Imaging (SWI)/T2* GRE

• May show punctate microhemorrhages in some cases
• SWI is 3-6 times more sensitive than conventional T2* GRE for detecting small hemorrhagic lesions 4

Contrast Enhancement

• Typically minimal to no enhancement in acute phase
• Contrast administration is not necessary for diagnosis of FES 4

Differential Diagnosis Using MRI

Fat embolism syndrome can be differentiated from diffuse axonal injury (DAI) using MRI with the following features:

1. Distribution pattern: FES shows more diffuse, symmetric distribution compared to DAI's more asymmetric pattern

2. Diffusion characteristics:

   • FES: Predominantly vasogenic edema (increased ADC)
   • DAI: Predominantly cytotoxic edema (decreased ADC) 3

3. DTI parameters:

   • FES: Higher radial diffusivity (RD) and lower fractional anisotropy (FA)
   • DAI: Less pronounced changes in RD and FA 3

Clinical Correlation and Timing

• MRI abnormalities typically appear 24-72 hours after the initial trauma or orthopedic procedure
• MRI findings may persist for weeks but often resolve completely over time
• MRI is significantly more sensitive than CT for detecting cerebral fat embolism 1
• Brain CT is typically normal or may show only subtle, nonspecific low-density areas 1

Diagnostic Algorithm

1. Consider FES in patients with:

   • Long bone fractures or orthopedic procedures
   • Altered mental status, confusion, or focal neurologic deficits
   • Respiratory distress and/or petechial rash

2. Initial imaging:

   • Brain CT may be performed initially but is often normal
   • Proceed to brain MRI if clinical suspicion remains high despite normal CT

3. Optimal MRI protocol:

   • T1-weighted imaging
   • T2-weighted and FLAIR sequences
   • DWI with ADC mapping
   • SWI or T2* GRE sequences
   • Consider DTI if available and differential with DAI is needed 4, 3

Clinical Implications

Early diagnosis of cerebral fat embolism using MRI is crucial for:

• Differentiating from other causes of altered mental status
• Guiding supportive management
• Providing prognostic information
• Avoiding unnecessary interventions for misdiagnosed conditions

MRI should be considered the first-line imaging modality when cerebral fat embolism is suspected, as it has significantly higher sensitivity than CT and can detect the characteristic "starfield" pattern of lesions 1, 2.