What does fat stranding on imaging studies indicate?

What Fat Stranding Means on Imaging

Fat stranding is an abnormally increased attenuation (hazy increased density) in fat tissue on CT imaging that represents inflammatory changes, edema, or regional free fluid—serving as a highly sensitive radiological clue to identify underlying pathology. 1

Radiological Appearance

• On CT imaging, fat stranding appears as hazy increased density in normally dark fat tissue 1
• On MRI, it demonstrates high T2 signal intensity 1
• This finding is distinct from fat thickening ("creeping fat"), which refers to increased volume of fat tissue rather than inflammatory changes 1, 2

Clinical Significance

• Fat stranding is a highly sensitive sign for detecting underlying pathology and serves as a critical clue to identify the source of inflammation 1
• The presence, extent, and pattern of fat stranding help narrow the differential diagnosis and guide clinical management 3
• "Disproportionate" fat stranding—where stranding is more severe than expected for the degree of bowel wall thickening—suggests a narrower differential diagnosis centered in the mesentery 3

Common Clinical Conditions Associated with Fat Stranding

Gastrointestinal Pathology

• Diverticulitis: Pericolonic fat stranding with bowel wall thickening and diverticula 1
• Peptic ulcer disease/gastritis: Fat stranding along the gastroduodenal region due to inflammation, often with mucosal hyperenhancement 4
• Inflammatory bowel disease: Fat stranding indicates active inflammation, particularly in Crohn's disease where wall edema, ulcers, and lymphadenopathy may be present 4, 1
• Appendicitis: Fat stranding around a dilated, fluid-filled appendix 3

Other Abdominal Conditions

• Acute cholecystitis: Perivesicular fat stranding indicating active gallbladder inflammation 1
• Pelvic inflammatory disease: Pelvic fat stranding with fluid and peritoneal thickening 5
• Necrotizing fasciitis: Fat stranding with skin thickening and fluid or gas in fascial planes 1
• Omental infarction and epiploic appendagitis: Disproportionate fat stranding with minimal bowel wall thickening 6, 3
• Mesenteric ischemia and bowel trauma: Mesenteric fat stranding (34% sensitivity, 92% specificity for bowel injury) 2

Imaging Optimization

• Contrast-enhanced CT is the preferred modality for visualizing fat stranding, as it provides better tissue characterization and allows detection of abnormal enhancement 1, 5
• Non-contrast CT has lower sensitivity for detecting subtle fat stranding 1
• MRI with fat-suppressed sequences can detect fat stranding with high sensitivity, particularly useful when radiation exposure is a concern 1, 2

Diagnostic Patterns That Guide Management

Extent and Distribution

• Multiple areas of fat stranding are significantly associated with malignant tumors (p = 0.040) 7
• Single area involvement is more common in benign tumors and inflammatory conditions 7
• Fat stranding is always located around the underlying lesion 7

Pattern Recognition

• Reticular pattern is the most common presentation regardless of etiology 7
• Reticulonodular pattern is a significant predictor of malignant tumor (p = 0.022) 7
• Disproportionate fat stranding (stranding >> bowel wall thickening) suggests diverticulitis, epiploic appendagitis, omental infarction, or appendicitis 3

Clinical Pitfalls

• Fat stranding is non-specific and requires correlation with other imaging findings, clinical presentation, and laboratory values 1
• Similar fat stranding patterns can occur in different conditions (e.g., pericolonic stranding in diverticulitis vs. perienteric stranding in IBD), requiring careful evaluation of associated findings 5
• In gastroduodenal perforation, fat stranding along the gastroduodenal region occurs in 89% of cases but must be combined with other findings like wall defects (positive likelihood ratio 36.83) for accurate diagnosis 4