What is fat stranding in a medical context?

What Fat Stranding Means in Medical Imaging

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

Radiological Appearance

• On CT scans, fat stranding appears as hazy increased density in normally dark (low-attenuation) fat tissue 1
• On MRI, it manifests as high T2 signal intensity in fat-suppressed sequences 1
• This finding is distinct from "fat thickening" (also called "creeping fat"), which refers to increased volume of fat tissue rather than inflammatory changes 1

Clinical Significance and Interpretation

Fat stranding is a highly sensitive but non-specific finding that indicates active inflammation or pathology in the adjacent structures 1. The key is recognizing that fat stranding always occurs around the underlying lesion and helps localize the source of disease 2.

Pattern Recognition Matters

• Reticular pattern is the most common presentation across all etiologies 3
• "Disproportionate" fat stranding (stranding more severe than expected for the degree of adjacent organ abnormality) suggests mesentery-centered pathology: diverticulitis, epiploic appendagitis, omental infarction, or appendicitis 2
• Multiple areas of involvement with reticulonodular pattern significantly predicts malignant tumors over benign processes 3

Common Clinical Conditions Associated with Fat Stranding

Gastrointestinal Pathology

• Diverticulitis: Pericolonic fat stranding is one of the most common CT findings, appearing alongside bowel wall thickening and visible diverticula 4, 1
• Peptic ulcer disease/gastritis: Fat stranding along the gastroduodenal region indicates inflammation, often with mucosal hyperenhancement and submucosal edema 4
• Inflammatory bowel disease: Perienteric or mesenteric fat stranding indicates active inflammation 1, 5
• Appendicitis: Fat stranding around a dilated, fluid-filled appendix 2

Other Abdominal/Pelvic Conditions

• Acute cholecystitis: Perivesicular fat stranding indicates active gallbladder inflammation 1
• Pelvic inflammatory disease: Pelvic fat stranding with fluid and peritoneal thickening 6
• Acute pyelonephritis: Perinephric fat stranding around inflamed kidneys 7
• Necrotizing fasciitis: Fat stranding with skin thickening and fluid/gas in fascial planes 1
• Bowel trauma: Mesenteric fat stranding is 34% sensitive and 92% specific for bowel injury 5

Imaging Optimization

Contrast-enhanced CT is the preferred modality for detecting and characterizing fat stranding 4, 1, 6. Here's why:

• IV contrast significantly improves visualization of mucosal enhancement, wall hyperenhancement, and abscess formation 4, 6
• Non-contrast CT has substantially lower sensitivity for detecting subtle fat stranding 1, 5
• Neutral oral contrast (water or dilute barium) is preferred over positive contrast when evaluating for mucosal disease, as it allows better assessment of mucosal enhancement 4
• MRI with fat-suppressed sequences can detect fat stranding with high sensitivity when radiation exposure is a concern 1, 5

Critical Pitfalls to Avoid

• Do not assume fat stranding alone indicates severity: The extent and pattern matter more than presence alone 3, 2
• Single area involvement typically suggests benign inflammatory processes, while multiple areas raise concern for malignancy or severe disease 3
• Always correlate with clinical presentation: Fat stranding in colon cancer occurs more frequently with increasing circumferential tumor proportion (≥75%) and longitudinal length, but doesn't reliably distinguish depth of invasion beyond subserosal infiltration 8
• In immunocompromised patients, maintain a lower threshold for aggressive management even with modest fat stranding, as these patients are at higher risk for complicated disease 1

Diagnostic Approach Based on Location

• Pericolonic stranding: Consider diverticulitis (with diverticula), inflammatory bowel disease (with bowel wall changes), or colon cancer (with mass) 4, 1
• Mesenteric stranding: Evaluate for bowel injury in trauma, mesenteric ischemia, or inflammatory bowel disease 5
• Perivesicular stranding: Acute cholecystitis is the primary consideration 1
• Periarterial stranding around celiac/superior mesenteric arteries: Consider visceral disseminated varicella-zoster virus infection in immunocompromised patients 9