What is fat stranding?

Fat Stranding: Radiological Finding and Clinical Significance

Fat stranding is a radiological finding on CT imaging characterized by increased attenuation (hazy increased density) in fat tissue due to inflammatory changes, representing edema within the fat. 1

Definition and Appearance

• Fat stranding appears as abnormally increased attenuation in fat tissue, often associated with regional free fluid or edema, representing inflammatory changes 1
• On CT images, it appears as hazy increased density, while on MRI it shows high T2 signal intensity 1
• This finding is distinct from fat thickening (also called "creeping fat"), which refers to increased volume of fat tissue rather than just inflammatory changes 1

Clinical Significance

• Fat stranding is a highly sensitive sign for detecting underlying pathology, serving as a clue to identify the source of inflammation 1
• It is always located around the underlying lesion, making it useful for localizing the primary problem 2
• "Disproportionate" fat stranding (more severe than expected for the degree of bowel wall thickening) suggests specific conditions centered in the mesentery, including diverticulitis, epiploic appendagitis, omental infarction, and appendicitis 3

Common Conditions Associated with Fat Stranding

• Necrotizing fasciitis: Fat stranding is one of the typical CT findings, along with skin thickening and fluid or gas in fascial planes 4
• Diverticulitis: Pericolonic fat stranding is a characteristic finding, along with bowel wall thickening and diverticula 4, 5
• Appendicitis: Fat stranding with free fluid on CT is significantly associated with complicated appendicitis 6
• Inflammatory bowel disease: Indicates active inflammation 1
• Trauma: Fat stranding is often seen in multiple areas in cases of trauma 2
• Malignancy: More common in malignant tumors (44%) than benign tumors (12%), and typically involves multiple areas in malignant cases 2

Patterns and Distribution

• The pattern of fat stranding can help narrow the differential diagnosis 2:
  • Reticular pattern (interconnected linear strands) is the most common presentation 2
  • Reticulonodular pattern is significantly associated with malignant tumors 2
  • Single-area involvement is more common in inflammation and benign tumors 2
  • Multiple-area involvement is more common in malignant tumors and trauma 2

Factors Affecting Fat Stranding Appearance

• Patient factors that increase likelihood of fat stranding in acute conditions include:
  • Age ≥40 years 7
  • Body mass index ≥23 kg/m² 7
  • Elevated inflammatory markers (WBC ≥10,000/μl, C-reactive protein ≥2.4 mg/dl) 7
• In colon cancer, fat stranding is more frequent with increasing circumferential proportion of the tumor and greater longitudinal length 8

Imaging Considerations

• Fat stranding is best visualized on contrast-enhanced CT 1
• Non-contrast CT has lower sensitivity for detecting subtle fat stranding 1
• MRI can also detect fat stranding with high sensitivity, especially with fat-suppressed sequences 1

Fat stranding serves as an important radiological sign that can guide clinicians to the underlying pathology, though it remains a non-specific finding that requires correlation with other clinical and imaging features for definitive diagnosis.