Vascular Disorders of Intestine

IBD: Pathophysiology - Gut's Blood Crisis

Definition: Intestinal ischemia: critical gut injury from severely insufficient blood supply.

• Etiology:

  • Occlusive (vascular blockage):
    • Arterial: Embolism (e.g., Atrial Fibrillation - AF), thrombosis (atherosclerosis).
    • Venous: Thrombosis (e.g., hypercoagulable states, portal HTN).
  • Non-occlusive (low flow states): Shock (cardiogenic, hypovolemic, septic), potent vasopressors.

• Pathophysiology:

  • Hypoxic Injury: Initial damage from $↓O₂$; leads to $↓ATP$, cell swelling, mucosal barrier compromise.
  • Reperfusion Injury: Paradoxical exacerbated damage on reperfusion; driven by reactive oxygen species ($↑ROS$), neutrophils, inflammatory mediators.

• Key Risk Factors:

  • Atherosclerosis (major for arterial occlusion)
  • Atrial Fibrillation (AF) (key emboli source)
  • Shock (all types cause hypoperfusion)
  • Vasculitis (e.g., PAN, SLE)
  • Hypercoagulable states
  • Advanced age, prior abdominal surgery.

⭐ Watershed areas (splenic flexure, rectosigmoid junction) are most vulnerable to ischemia due to limited collateral circulation.

IBD: Morphology - Damage Unveiled

• Spectrum of Infarction (Ischemic Bowel Disease):
  • Mucosal: Superficial necrosis, mucosa only; due to hypoperfusion.
  • Mural: Necrosis extends into submucosa; from severe hypoperfusion or partial occlusion.
  • Transmural: Full-thickness necrosis involving all layers; typically acute arterial occlusion.
• Gross Features:
  • Affected segment: Segmental or diffuse; sharply demarcated in arterial occlusion.
  • Color: Dusky, cyanotic to purple-red, later hemorrhagic.
  • Wall: Edematous, thickened.
  • Mucosa: Ulceration, friability, sloughing. Perforation in severe transmural cases.
• Microscopic Features:
  • Early: Coagulative necrosis, edema, hemorrhage.
  • Epithelium: Villous blunting/atrophy, crypt destruction.
  • Inflammation: Neutrophils, later chronic inflammation. Pseudomembrane formation.
• Watershed Areas (Most Vulnerable):
  • Splenic flexure (Griffiths' point): SMA & IMA junction.
  • Rectosigmoid junction (Sudeck's point): IMA & iliac artery supply.

⭐ Transmural infarction often presents with bloody diarrhea and can rapidly progress to sepsis and shock.

IBD: Clinical Syndromes - Gut Attack Scenarios

Vascular compromise leading to intestinal injury. High index of suspicion is key.

• Acute Mesenteric Ischemia (AMI): Life-threatening!
  • Causes:
    • Arterial embolism (e.g., AFib) / thrombosis (atherosclerosis)
    • Non-Occlusive Mesenteric Ischemia (NOMI; low flow states)
    • Mesenteric venous thrombosis (hypercoagulable states)
  • Sx: Severe, acute abdominal pain "out of proportion" to physical findings.
  • Dx: CT Angiography (CTA) is gold standard. ↑Lactate.
  • Mortality: High (>50-70%).
• Chronic Mesenteric Ischemia (CMI):
  • "Intestinal angina": Postprandial abdominal pain, food fear, weight loss.
  • Dx: CTA.
• Ischemic Colitis (IC):
  • Most common form of intestinal ischemia.
  • Often transient, segmental inflammation (watershed areas).
  • Sx: LLQ pain, hematochezia.

⭐ Ischemic colitis most commonly affects watershed areas, particularly the splenic flexure and sigmoid colon.

Other Vascular Lesions - Bleeding Mysteries

• Angiodysplasia:
  • Pathogenesis: Acquired; ectatic, thin-walled submucosal vessels.
  • Location: Cecum & right colon (most common). 📌 Right side, Right site!
  • Associations: Aortic stenosis (Heyde's syndrome), von Willebrand Disease (vWD), End-Stage Renal Disease (ESRD).
  • Presentation: Recurrent, painless Lower GI Bleeding (LGIB) (occult or melena).
• Radiation Enterocolitis/Proctitis:
  • Cause: Post-pelvic radiation therapy (XRT).
  • Path: Chronic ischemia, obliterative endarteritis, submucosal fibrosis, telangiectasias.
  • Sx: Rectal bleeding, pain, diarrhea, strictures.
• Necrotizing Enterocolitis (NEC):
  • Population: Premature infants, low birth weight.
  • Path: Ischemic necrosis (typically terminal ileum/colon); gas in bowel wall (pneumatosis intestinalis).
  • Sx: Bloody stools, abdominal distension, feeding intolerance.

⭐ Heyde's syndrome triad: Aortic stenosis, acquired vWD (Type 2A)-like defect, and bleeding from GI angiodysplasia. Bleeding often improves after aortic valve replacement!

High‑Yield Points - ⚡ Biggest Takeaways

• Ischemic bowel disease most commonly affects watershed areas like the splenic flexure and sigmoid colon.
• Acute mesenteric ischemia (AMI) presents with severe abdominal pain out of proportion to clinical findings, often due to arterial embolism.
• Chronic mesenteric ischemia (CMI) is characterized by postprandial abdominal pain ("intestinal angina") and weight loss, typically from atherosclerosis.
• Non-occlusive mesenteric ischemia (NOMI) is seen in critically ill patients, often associated with shock or vasopressor use.
• Colonic ischemia is the most common form of intestinal ischemia; thumbprinting may be seen on imaging.
• Angiodysplasia is a frequent cause of lower GI bleeding in the elderly, commonly found in the cecum and right colon.
• Hemorrhoids are dilated submucosal veins in the anal canal, a common cause of painless rectal bleeding with defecation.