What does fat stranding on Contrast-Enhanced Computed Tomography (CECT) signify?

Fat Stranding on CECT: Significance and Clinical Implications

Fat stranding on contrast-enhanced CT (CECT) signifies inflammation or infiltration of fat tissue and is a critical indicator of active pathological processes in the adjacent structures, helping to identify the location and severity of disease.

Definition and Appearance

• Fat stranding appears as increased attenuation (density) in fat tissue on CT images
• Characterized by linear or reticular densities within the normally homogeneous, low-density fat
• Represents edema and inflammatory changes within fat tissue

Clinical Significance

Primary Indicator of Active Inflammation

• Serves as a key marker of active inflammatory processes 1
• Significantly associated with underlying pathology (present in 38% of abdominal disorders) 2
• When present with other CT signs (like bowel wall thickening >6mm and absence of intraluminal gas), increases the odds ratio of appendicitis to 6.8 1

Diagnostic Value in Specific Conditions

Appendicitis

• Fat stranding is a significant predictor of appendicitis when combined with other findings 1
• Present in 34.1% of appendicitis cases versus 8.9% in non-appendicitis cases (P = 0.001) 1
• More common in patients ≥40 years, BMI ≥23 kg/m², elevated WBC count (≥10,000/μl), and CRP level ≥2.4 mg/dl 3

Diverticulitis

• Pericolonic fat stranding is a cardinal sign of active diverticulitis 1
• Often seen adjacent to the sigmoid colon with scattered colonic diverticula 1
• Helps identify the offending diverticulum at the epicenter of inflammatory changes 1

Inflammatory Bowel Disease

• Perienteric inflammation/fat stranding indicates more severe inflammation 1
• Associated with elevated C-reactive protein levels 1
• Considered a responsive feature that can improve after medical therapeutic intervention 1

Colon Cancer

• Present in 36.8% of colon cancer cases 4
• More frequent with increasing circumferential proportion of tumor (especially ≥75%) 4
• More common with increasing longitudinal length of tumor 4

Vascular Pathology

• May be the only indicator of spontaneous isolated superior mesenteric artery dissection, especially in early stages 5
• Can serve as a marker requiring further investigation with CT angiography 5

Pattern Recognition and Differential Diagnosis

"Disproportionate" Fat Stranding

• When fat stranding is more severe than expected for the degree of bowel wall thickening 6
• Narrows differential diagnosis to conditions centered in the mesentery:
  • Diverticulitis
  • Epiploic appendagitis
  • Omental infarction
  • Appendicitis

Distribution Patterns

• Single area involvement: More common in benign tumors and inflammatory conditions 2
• Multiple area involvement: More suggestive of malignant tumors or trauma 2
• Reticular pattern: Most common presentation regardless of etiology 2
• Reticulonodular pattern: Significant predictor of malignancy 2

Clinical Applications

Guiding Treatment Decisions

• Helps differentiate active inflammation (which may respond to medical therapy) from fibrotic strictures (which may require surgery) 1
• Assists in identifying complications such as abscess formation that may require drainage 1
• Can indicate severity of pancreatitis when present in peripancreatic regions 1

Monitoring Treatment Response

• Can be used to assess response to medical therapy in inflammatory conditions 1
• Reduction in fat stranding may indicate transmural response or remission 1

Pitfalls and Limitations

• Non-specific finding that must be interpreted in clinical context 2, 6
• May be influenced by patient factors such as age, body mass index, and inflammatory marker levels 3
• Can be present in both benign and malignant conditions 2, 4
• May be subtle or absent in early disease or immunocompromised patients

Conclusion

Fat stranding on CECT is a valuable radiological sign that helps localize pathology, assess disease severity, guide differential diagnosis, and monitor treatment response. While non-specific on its own, when combined with other imaging findings and clinical information, it significantly enhances diagnostic accuracy and clinical decision-making.