Acute Diverticulitis of the Sigmoid Colon
Colonic wall thickening and pericolic fat stranding of the sigmoid colon indicates acute diverticulitis until proven otherwise. 1, 2, 3
Primary Diagnosis
The combination of these two imaging findings is highly characteristic of acute diverticulitis, with CT demonstrating sensitivity and specificity as high as 100% for this diagnosis. 1, 4 The American College of Radiology identifies pericolonic fat stranding and bowel wall thickening as the most common CT findings in acute diverticulitis, particularly when diverticula are also present. 1, 2, 3
Key Diagnostic Features Supporting Diverticulitis
CT findings that confirm the diagnosis include:
- Segmental colonic wall thickening (>5 mm) in the sigmoid colon, which is the most commonly affected segment 2, 3, 4
- Pericolonic fat stranding representing inflammatory changes in the mesenteric fat surrounding the affected bowel 1, 2, 3
- Presence of diverticula at the epicenter of inflammatory changes 1, 3
- Additional supportive findings may include an inflamed diverticulum, the "arrowhead sign" (contrast material at the orifice of inflamed diverticulum), or muscular hypertrophy 1, 3
Clinical Context
When these imaging findings occur with left lower quadrant pain, fever, and changes in bowel habits, the diagnosis of acute diverticulitis is essentially confirmed. 1, 4 The American Academy of Family Physicians reports that left lower quadrant pain with mild tenderness is the most common presenting symptom in adults with diverticulitis. 4
Critical Differential Considerations
While diverticulitis is the primary diagnosis, you must exclude:
- Colonic malignancy: Focal, irregular, and asymmetric wall thickening suggests malignancy rather than diverticulitis 5. Diverticulitis typically shows smooth, symmetric wall thickening 1, 6
- Segmental colitis associated with diverticulosis (SCAD): This presents with isolated sigmoid inflammation but is a chronic condition rather than acute 7
- Inflammatory bowel disease (Crohn's disease): Can cause perienteric fat stranding, but typically has different distribution patterns 8
Distinguishing Features Favoring Diverticulitis Over Malignancy
The pattern of fat stranding is diagnostically important:
- "Disproportionate" fat stranding (stranding more severe than expected for the degree of wall thickening) strongly suggests diverticulitis rather than malignancy 6
- Smooth, symmetric wall thickening with no lymphadenopathy favors diverticulitis 6
- Short-segment involvement centered around diverticula is characteristic of diverticulitis 2
Assessment for Complications
CT should be carefully reviewed for complications that alter management:
- Pericolic abscess: Rim-enhancing fluid collection adjacent to affected bowel (present in ~35% of cases) 3
- Free perforation: Extraluminal gas distant from the affected segment (>5 cm away) 3
- Fistula formation: Communication with adjacent organs 3
- Bowel obstruction: From chronic muscular hypertrophy and luminal narrowing 9
Abscesses ≥3 cm typically require percutaneous catheter drainage, while free perforation and peritonitis require surgical intervention. 3
Management Implications
Uncomplicated diverticulitis (wall thickening and fat stranding without abscess, perforation, or fistula) can be managed medically with antibiotics and bowel rest. 4 Red flags requiring more aggressive intervention include fever, inability to pass gas/stool, severe tenderness with guarding, vomiting, or signs of shock. 4
Colonoscopy must be performed 6-8 weeks after resolution of acute symptoms to exclude underlying malignancy, as recommended by the American College of Gastroenterology. 4 This is critical because adenocarcinoma can coexist with diverticular disease in more than 15% of patients. 10
Prognostic Information
Colonic wall thickness on CT has prognostic value: patients with wall thickness <9 mm have a 19% recurrence risk, which helps guide decisions about elective surgical resection. 2