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

MRI Brain Findings in Fat Embolism Syndrome (FES)

The characteristic MRI findings in fat embolism syndrome include multiple small, scattered 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

Typical MRI Findings in FES

Key Imaging Characteristics

• Distribution pattern: Multiple small (2-15mm), non-confluent, scattered lesions in a "starfield" pattern 3
• Anatomical location: Predominantly in subcortical and deep white matter, centrum semiovale, cerebellum, and occasionally basal ganglia 2, 4
• Signal characteristics:
  • Hyperintense on T2-weighted and FLAIR sequences 1, 3
  • Variable appearance on DWI with predominantly high signal 5
  • Predominantly vasogenic edema pattern (increased radial diffusivity) rather than cytotoxic edema 6

Sequence-Specific Findings

• DWI (Diffusion-Weighted Imaging): Shows multiple bright lesions that often represent vasogenic edema rather than true restriction 5
• T2/GRE or SWI:* May show petechial hemorrhages in some cases 1
• T1-weighted imaging: Usually normal or may show subtle hypointense lesions 2

Diagnostic Value of MRI in FES

MRI is significantly more sensitive than CT for detecting cerebral fat embolism. CT scans are typically negative or show only subtle, nonspecific findings in FES patients 3, 2. MRI should be considered the first-line neuroimaging modality when cerebral fat embolism is suspected 3.

The sensitivity, specificity, and accuracy of conventional MRI in diagnosing cerebral FES are approximately 76%, 85%, and 80%, respectively 6.

Differentiating FES from Other Conditions

FES vs. Diffuse Axonal Injury (DAI)

• Distribution: FES shows more uniform, bilateral distribution compared to DAI 6
• DTI findings: FES shows higher radial diffusivity and lower fractional anisotropy compared to DAI 6
• Mechanism: FES lesions primarily represent vasogenic edema, while DAI shows more cytotoxic edema 6

Timing of Imaging

• MRI abnormalities typically appear 24-72 hours after the initial trauma or precipitating event 2, 4
• Follow-up imaging may show resolution of lesions within weeks to months 5

Clinical Correlation

Neurological manifestations of FES typically occur 12-72 hours after the initial insult (usually long bone fractures) 4. These include:

• Altered mental status ranging from confusion to coma
• Focal neurological deficits
• Seizures
• Autonomic dysfunction

MRI findings should be correlated with clinical features, which may include the classic triad of respiratory distress, neurological abnormalities, and petechial rash 2.

Pitfalls and Considerations

• Cerebral fat embolism may occur without respiratory or dermatological signs, making neuroimaging crucial for diagnosis 4
• Initial CT scans are often negative, potentially leading to missed or delayed diagnosis 3
• Early MRI (within 24 hours of symptom onset) is recommended when FES is suspected 7
• A comprehensive MRI protocol should include T2-weighted, FLAIR, DWI, and T2*/GRE or SWI sequences 1, 7

In conclusion, MRI is the imaging modality of choice for diagnosing cerebral fat embolism syndrome, with characteristic findings that can help differentiate it from other neurological conditions, particularly when clinical suspicion is high despite negative CT findings.