What are the causes of ileal strictures?

Causes of Ileal Strictures

The most common causes of ileal strictures include Crohn's disease, intestinal tuberculosis, NSAID-induced enteropathy, radiation enteropathy, adhesions, and malignancy, with Crohn's disease being the predominant etiology in developed countries. 1

Primary Causes of Ileal Strictures

1. Inflammatory Bowel Disease

• Crohn's Disease: The leading cause of ileal strictures in developed countries
  • Up to 50% of Crohn's patients develop strictures during their disease course 2
  • Pathophysiology: Two distinct types of strictures have been identified 3:
    • Hypertrophic strictures: Characterized by concentrically thickened walls with 3-fold increases in cross-sectional area, high transmural inflammation, and significant fibromuscular tissue
    • Constrictive strictures: Feature thin, pliant walls with minimal fibromuscular expansion, low inflammation scores, and are often multiple (2-4 per specimen)
  • Most Crohn's strictures contain both inflammatory and fibrotic components 1

2. Infectious Causes

• Intestinal tuberculosis: Common cause in endemic regions 4
  • Usually responds well to anti-tubercular therapy
  • May require fewer endoscopic dilatation sessions compared to Crohn's disease strictures
• Post-infectious strictures: Can occur following severe bacterial enteritis

3. Medication-Induced

• NSAID enteropathy: Can cause diaphragm-like strictures 1
  • Typically occurs with long-term NSAID use
  • Often presents as multiple, thin, circumferential strictures

4. Radiation-Induced

• Radiation enteropathy: Following radiotherapy for abdominal or pelvic malignancies 1
  • Characterized by progressive fibrosis and vascular damage
  • Usually occurs within the radiation field

5. Post-Surgical

• Adhesions: Can mimic Crohn's disease strictures on imaging 1
  • Usually at sites of previous surgery or inflammation
• Anastomotic strictures: Common after ileocolic resection
  • Often develop at surgical anastomosis sites

6. Vascular Causes

• Ischemic strictures: Due to mesenteric vascular insufficiency 5
  • Can develop rapidly (within months)
  • May be caused by superior mesenteric artery thrombosis
• Chronic mesenteric venous occlusion: Can lead to stricture formation 1

7. Neoplastic Causes

• Malignancy: Should be suspected with focal stenoses >1.5 cm in diameter 1
  • Look for mass effect, extension into adjacent mesentery
  • Particularly concerning in patients with longstanding poorly controlled Crohn's disease 1

Imaging Features of Ileal Strictures

Diagnostic Criteria

• A stricture is definitively present when there is:
  • Luminal narrowing with proximal small bowel dilation >3 cm 1
  • Fixed narrowing on multiple imaging sequences or serial examinations 1

Severity Classification

• Mild upstream dilation: 3-4 cm lumen diameter
• Moderate to severe upstream dilation: >4 cm lumen diameter 1

Associated Features to Report

• Length of stricture (critical for treatment planning)
• Presence of active inflammation (hyperenhancement, edema)
• Fibrotic features (lack of enhancement, decreased T2 signal)
• Associated complications (fistulae, abscesses, perforations) 1

Clinical Pitfalls and Caveats

1. Misdiagnosis risk: Similar-appearing strictures may have different etiologies, even in patients with known Crohn's disease 5

   • Consider alternative diagnoses when:
     • Stricture location differs from previous disease pattern
     • Rapid progression occurs (weeks to months)
     • Poor response to anti-inflammatory treatment

2. Imaging limitations: Conventional cross-sectional imaging techniques cannot reliably distinguish inflammation from fibrosis 6

   • Most strictures contain varying degrees of both components
   • Treatment decisions should not be based solely on imaging appearance

3. Multiple strictures: When multiple strictures are present close together, consider:

   • Constrictive Crohn's disease (67% of constrictive strictures occur multiply) 3
   • Tuberculosis (often multifocal)
   • NSAID enteropathy (typically multiple)

4. Malignancy risk: Always evaluate for malignancy in:

   • Patients with longstanding poorly controlled disease
   • Asymmetric or nodular strictures
   • Strictures with soft tissue extension into mesentery 1

5. Downstream stricture identification: When strictures are in close proximity, the ability to detect downstream strictures is compromised as the upstream stricture already causes obstruction 1

By understanding the diverse etiologies of ileal strictures and their distinguishing features, clinicians can develop appropriate diagnostic and treatment strategies to optimize patient outcomes and quality of life.