Ischemic Colitis - A Comprehensive Surgery Guide (Final Year MBBS)

Definition & Epidemiology

Aetiology

Vascular Anatomy - Key to Understanding

1. Marginal artery of Drummond - runs parallel to the mesenteric margin of the entire colon; absent at the splenic flexure in up to 18-50% of people
2. Arc of Riolan (meandering mesenteric artery) - connects SMA to IMA near the mesenteric root; its presence indicates major mesenteric artery obstruction

Watershed Areas (Most Vulnerable Sites)

The rectum is relatively spared due to its rich dual blood supply.

Classification by Mechanism

• Sabiston Textbook of Surgery 21e

Pathogenesis

1. Initial ischemic phase: During hypotension, blood is shunted away from splanchnic circulation toward the brain and heart. Mucosal injury begins within 20 minutes to 1 hour of decreased blood flow.
2. Transmural progression: If ischemia continues, injury spreads from mucosa → submucosa → muscularis → serosa. Transmural infarction occurs within 8-16 hours.
3. Reperfusion injury: When blood flow is restored, reactive oxygen species (ROS) are released, causing lipid peroxidation and cell necrosis - causing additional injury beyond the initial ischemic insult.
4. Histological sequence: Initial changes on the antimesenteric side of the mucosa. Progresses to loss of surface epithelium, crypt necrosis, mucin depletion, hyalinosis of the lamina propria, and eventually ghost crypts.

Depth of Injury Determines Outcome

Risk Factors

• Advanced age, female sex
• Atherosclerotic disease (ischemic heart disease, cerebrovascular disease, peripheral vascular disease)
• Diabetes mellitus, hypertension, COPD, CKD/renal disease
• Heart failure, atrial fibrillation, septic shock, hemorrhagic shock
• IBD, IBS, constipation
• COVID-19 (recently identified association)

• Diuretics, digoxin (cardiovascular drugs)
• Psychotropic medications
• Immunosuppressants, NSAIDs
• Cocaine, amphetamines (vasoconstrictors)
• Oral contraceptives (thrombogenic)

• Aortic surgery (AAA repair - most common postoperative cause)
• Cardiac surgery with prolonged cross-clamping
• Endovascular abdominal procedures (including chemoembolization)
• Post-colonoscopy
• Sabiston 21e, Box 95.6

Isolated Right-Sided Colon Ischemia (IRCI) - Special Entity

• 30-day mortality: 20.3% vs 9.0% in non-IRCI
• Surgical intervention required in 40.9% vs 10.3% in non-IRCI
• More associated with coronary artery disease and CKD on hemodialysis
• Must always prompt CT angiography to exclude acute mesenteric ischemia

Clinical Features

Symptoms

• Classic triad: Sudden-onset crampy abdominal pain (usually left lower quadrant) + urgent desire to defecate + hematochezia within 24 hours of pain
• Tenesmus
• Rectal bleeding: more common in non-IRCI (69.9%) than IRCI (39.4%)

Signs by Severity

Key exam point: Pain out of proportion to examination, especially WITHOUT rectal bleeding, should raise suspicion for IRCI or acute mesenteric ischemia.

Investigations

Laboratory

• Leukocytosis (frequent)
• Elevated lactate (>2.5 mmol/L - poor prognostic sign)
• Elevated LDH, urea, creatinine
• Low hemoglobin, low albumin
• Metabolic acidosis with base deficit in severe cases
• Stool: C. difficile toxin, culture/sensitivity, ova and parasites (to exclude infectious cause)

Imaging

• "Thumbprinting" - rounded densities along sides of gas-filled colon; represents mucosal edema and submucosal hemorrhage (nonspecific)
• Free air under diaphragm = perforation → immediate surgery

• Segmental bowel wall thickening
• Pericolonic fat stranding
• Thumbprinting
• Pneumatosis intestinalis (gas in colonic wall) - severe transmural disease
• Portal/mesenteric venous gas - transmural infarction; indicates need for emergency surgery
• Free air = perforation

CT angiography (multiphasic) indicated when IRCI is suspected or pain is severe without bleeding, to exclude major mesenteric arterial occlusion.

Endoscopy - Gold Standard

• Segmental erythema, edema, friable mucosa
• Petechial hemorrhage
• Mucosal ulceration
• Submucosal hemorrhagic nodules
• Involvement of watershed areas
• "Single stripe sign": single linear ulcer along the antimesenteric wall - rare but specific for IC
• Abrupt transition between injured and normal mucosa; rectal sparing (supports ischemia over IBD)
• In severe ischemia: gray-green or black mucosa
• After 48 hrs: ulcerations develop as submucosal hemorrhages resolve

Endoscopy cannot distinguish partial-thickness from full-thickness ischemia. Avoid overinsufflation.

Complications

• Schwartz's Principles of Surgery 11e; Sabiston 21e

Management

Conservative (Non-Operative) - 80% of patients

1. Bowel rest (NPO) + IV fluids (aggressive resuscitation)
2. Broad-spectrum antibiotics (to prevent bacterial translocation)
3. Nasogastric tube if ileus is present
4. Optimize hemodynamic status - treat heart failure, sepsis, hypotension
5. Discontinue causative drugs (vasoconstrictors, NSAIDs, etc.)
6. Adjuncts: phosphodiesterase-5 inhibitors, pentoxifylline, prostaglandin E1 (improve mucosal blood flow)
7. Serial clinical monitoring: if no improvement or worsening within 2-3 days, escalate

Indications for Emergency Surgery (Operative)

Surgical Approach

• Incision: Midline laparotomy (diagnostic laparoscopy in selected cases)
• Principle: Resect all grossly ischemic colon; assess entire small and large intestine
• Extent of resection: Anatomic resection ensuring adequate blood supply to remaining colon; intraoperative indocyanine green (ICG) infrared angiography increasingly used to assess bowel viability
• Anastomosis vs stoma:
  • Right-sided IC: Primary anastomosis safe if bowel well-perfused
  • Left-sided IC: Hartmann's procedure (end colostomy + rectal stump) is standard; reversal after 6-8 weeks; primary anastomosis +/- protective diverting ileostomy in selected stable cases
  • Pancolitis: Total colectomy with end ileostomy
• Second-look laparotomy: If viability uncertain, leave abdomen open (temporary closure), return in 12-48 hours to assess further necrosis
• No revascularization: Unlike small bowel ischemia, large vessel occlusion is rarely the cause; vascular reconstruction is not typically indicated

Post-Operative Follow-Up

• Colonoscopy after recovery to:
  • Evaluate for strictures
  • Rule out IBD, malignancy (mimics on endoscopy)

Mortality Risk Factors (Post-colectomy)

• Elderly age, poor functional status, multiple comorbidities
• Preoperative septic shock, blood transfusions, acute renal failure
• Delay from admission to surgery
• Peak preoperative lactate >2.5 mmol/L
• ASA class 4, subtotal/total colectomy, need for dialysis

Summary Algorithm

Suspected IC
     ↓
History + Exam + Labs (CBC, metabolic panel, lactate, stool cultures)
     ↓
CT Abdomen (with contrast)
     ↓
┌──────────────────────────────────────────┐
│ Signs of perforation/transmural ischemia │
│ (free air, portal gas, pneumatosis +     │
│  peritonitis, hemodynamic instability)   │
└──────────────────────────────────────────┘
        ↓ YES                   ↓ NO
   Emergency Surgery       Early Colonoscopy (within 48h)
   (Midline lap,                ↓
   resect ischemic colon,  Conservative Management
   Hartmann's for left-    (Bowel rest, IVF, ABx)
   sided disease)               ↓
                         Reassess in 2-3 days
                         ↓ No improvement or worsening
                         → Repeat imaging/endoscopy → Surgery

High-Yield Points for Exam

1. Most common GI ischemia and most common form is nonocclusive (due to low-flow states)
2. Watershed areas: Griffith's point (splenic flexure) and Sudeck's point (rectosigmoid) - both watershed, ~80% of cases
3. Classic presentation: Crampy LLQ pain + urgency + hematochezia within 24 hours
4. Thumbprinting on AXR/CT = mucosal edema/submucosal hemorrhage
5. Gold standard diagnosis: Colonoscopy within 48 hours; single stripe sign is specific
6. 80% managed conservatively with bowel rest, IVF, broad-spectrum antibiotics
7. Peritonitis + portal venous gas + pneumatosis intestinalis = emergency surgery
8. Hartmann's procedure for left-sided IC (NOT primary anastomosis)
9. IRCI (isolated right colon ischemia) = worst prognosis; suspect acute mesenteric ischemia
10. Long-term complications: Stricture (10-15%), chronic segmental ischemia (15-20%)