What are the possible causes of peritoneal enhancement and thickening observed on CT scan?

Causes of Peritoneal Enhancement and Thickening on CT Scan

Peritoneal enhancement and thickening on CT scan most commonly indicates inflammatory or infectious peritonitis, malignant peritoneal carcinomatosis, or sclerosing peritonitis, with the specific pattern of thickening (smooth vs. nodular) and associated findings being critical for narrowing the differential diagnosis.

Pattern-Based Diagnostic Approach

The morphologic characteristics of peritoneal thickening provide the most useful framework for differential diagnosis 1:

Smooth Peritoneal Thickening with Enhancement

• Infectious/Inflammatory Peritonitis: Most common acute cause

  • Associated findings: free fluid, pericolonic fat stranding, bowel wall thickening 2
  • In diverticulitis: pericolonic fat stranding, bowel wall thickening, diverticula visible 3
  • In pelvic inflammatory disease: pelvic fluid, hydrosalpinx, pyosalpinx, tubo-ovarian abscess 4
  • Perforated appendicitis: peritoneal thickening and enhancement is an independent predictor of perforation 5

• Sclerosing Peritonitis: Particularly in chronic ambulatory peritoneal dialysis patients

  • Diagnostic triad: peritoneal thickening/calcification (100%), loculated fluid collections (90%), small bowel tethering/dilatation (60%) 6
  • Peritoneal calcification is highly specific

Nodular or Irregular Peritoneal Thickening

• Peritoneal Carcinomatosis: Most important malignant cause

  • Distinguishing features from cirrhotic ascites 7:
    • Fluid in omental bursa (p=0.003)
    • Peritoneal thickening with enhancement (p=0.005)
    • Increased ascites density (p=0.01)
    • Tethered-bowel sign/loss of bowel mobility (p=0.001)
  • Common primary sources: ovarian, colon, stomach, pancreatic, appendiceal cancers 8, 9

• Peritoneal Tuberculosis: Important infectious mimic of carcinomatosis

  • Omental Rim sign: 85% sensitive, 96% specific for peritoneal TB vs. carcinomatosis 10
  • Can effectively rule out peritoneal carcinomatosis (96% specificity)

Critical Ancillary CT Findings

Fluid Collections

• Free intraperitoneal fluid and air: Suggests perforation of intraperitoneal colon segments (cecum, transverse, sigmoid) 2
• Loculated collections with rim enhancement: Indicates abscess formation 11
• Distribution pattern: Fluid in omental bursa strongly suggests malignancy over cirrhosis 7

Bowel Findings

• Bowel wall thickening with hyperenhancement: Active inflammation 11, 12
• Tethered bowel loops: Seen in carcinomatosis, sclerosing peritonitis, Crohn's disease 11, 7, 6
• Bowel dilatation: May indicate obstruction from adhesions or strictures 4, 6

Mesenteric Changes

• Mesenteric fat stranding: Inflammatory process 11, 3, 12
• "Comb sign": Engorged mesenteric vessels in Crohn's disease 11
• Mesenteric nodules: Suggests malignancy or granulomatous disease 11

Common Clinical Contexts

Post-Procedural

• Iatrogenic colonoscopy perforation: Look for pneumoperitoneum, peritoneal fluid, peritoneal enhancement 2
• Post-surgical: Consider anastomotic leak, particularly near surgical sites 11

Chronic Inflammatory Bowel Disease

• Crohn's disease: Peritoneal inflammation with penetrating complications (fistulas, inflammatory mass, abscess) 11
• Pouchitis: Wall thickening, mucosal hyperenhancement, peripouch stranding, peripouch abscess 13

Ischemic Bowel

• Mesenteric ischemia: Bowel wall thickening, hypoperfusion, mesenteric fat stranding, pneumatosis intestinalis 12
• Requires arterial phase imaging for optimal vascular assessment

Key Diagnostic Pitfalls

1. Peritoneal thickening without perforation: Transmural thermal injury after polypectomy can cause serosal irritation mimicking perforation 2

2. Small lesion detection: CT sensitivity drops dramatically for peritoneal implants <5 mm (11% sensitivity vs. 94% for lesions >5 cm) 14

3. Mucinous tumors: FDG-PET has poor sensitivity for mucinous peritoneal disease from appendiceal cancer 14

4. Distinguishing inflammation from fibrosis: Critical in Crohn's strictures, as medical treatment can alleviate inflammation but fibrotic strictures require surgery 11

Optimal Imaging Protocol

Contrast-enhanced CT with both IV and oral contrast is essential 2, 12:

• Arterial phase: For vascular assessment in ischemia
• Portal venous phase: For peritoneal and bowel wall evaluation
• Multi-planar reformations: Improve detection of subtle findings
• Rectal contrast: May help detect concealed perforations 2