What are the causes of ischemic colitis?

Causes of Ischemic Colitis

Ischemic colitis is primarily caused by four major pathophysiological mechanisms: arterial embolism (40-50% of cases), arterial thrombosis (25-40%), non-occlusive mesenteric ischemia (20-25%), and mesenteric venous thrombosis (<10%).

Major Causes by Pathophysiological Mechanism

1. Arterial Embolism (40-50% of cases)

• Cardiac sources:
  • Atrial fibrillation 1, 2
  • Left ventricular dysfunction with poor ejection fraction 1, 2
  • Valvular heart disease, particularly endocarditis 1, 2
  • Recent myocardial infarction 1
• Non-cardiac sources:
  • Atherosclerotic aorta (debris dislodgment) 1
  • Arterial debris dislodged during percutaneous interventions 1
• Emboli typically lodge 3-10 cm distal to superior mesenteric artery (SMA) origin 1, 2
• Over 20% of SMA emboli are associated with concurrent emboli to other arterial beds (spleen, kidney) 1

2. Arterial Thrombosis (25-40% of cases)

• Pre-existing chronic atherosclerotic disease leading to stenosis 1
• Often associated with history of chronic mesenteric ischemia (postprandial pain, weight loss, "food fear") 1
• Usually occurs at the origin of visceral arteries 1
• Other causes:
  • Vasculitis 1
  • Mesenteric dissection 1
  • Mycotic aneurysm 1
  • Arterial dissection 1

3. Non-Occlusive Mesenteric Ischemia (NOMI) (20-25% of cases)

• SMA vasoconstriction associated with low splanchnic blood flow 1
• Precipitating factors:
  • Severe cardiac failure 1
  • Sepsis 1
  • Hypovolemia 1
  • Use of vasoconstrictive agents 1
  • Hypotension and shock 2
  • Low mean arterial pressure (below 45 mmHg) 2

4. Mesenteric Venous Thrombosis (MVT) (<10% of cases)

• Attributed to Virchow's triad: stagnant blood flow, hypercoagulability, and endothelial damage 1
• Hypercoagulable states:
  • Inherited thrombophilias:
    • Factor V Leiden 1
    • Prothrombin mutation 1
    • Protein S deficiency 1
    • Protein C deficiency 1
    • Antithrombin deficiency 1
    • Antiphospholipid syndrome 1
  • Acquired thrombophilias:
    • Malignancies 1
    • Hematologic disorders 1
    • Oral contraceptives 1
• Inflammatory conditions:
  • Acute pancreatitis 1
  • Inflammatory bowel disease 1
  • Sepsis 1
  • Trauma 1
• Approximately 20% are idiopathic 1

Additional Risk Factors

• Advanced age (median age 70 years) 1
• Female gender (approximately two-thirds of patients) 1
• Pre-existing cardiovascular disease 1
• Institutionalized elderly patients 2
• Opioid medications 2
• Severe fecal impaction 2

Clinical Pearls and Pitfalls

1. Diagnostic challenge:

   • Ischemic colitis can be difficult to diagnose due to its nonspecific symptoms that mimic other abdominal pathologies 3
   • In ICU patients, diagnosis is particularly challenging as sedation or ventilation can mask characteristic features 3

2. High mortality risk:

   • Delayed diagnosis doubles mortality every 6 hours 2
   • Overall mortality remains high (50-80%) despite advances in treatment 2

3. Clinical presentation spectrum:

   • Ranges from transient, self-limiting ischemia to gangrenous colitis requiring urgent surgical intervention 4, 5
   • Classic presentation: abdominal pain out of proportion to physical findings 1, 2

4. Diagnostic approach:

   • Triple-phase CT is the gold standard initial imaging modality 2
   • Colonoscopy is considered the definitive diagnostic tool 3, 6
   • D-dimer elevation is a sensitive marker (no patient with normal D-dimer had intestinal ischemia) 2

Understanding these causes and risk factors is essential for early recognition and prompt intervention in ischemic colitis, which is crucial for improving outcomes in this potentially life-threatening condition.