Ischemic Colitis — Comprehensive Review

1. Definition & Epidemiology

• Initial hypoperfusion phase — mucosal ischemia begins within 20 minutes to 1 hour of reduced blood flow; transmural infarction occurs within 8–16 hours of sustained ischemia.
• Reperfusion injury — restoration of blood flow generates reactive oxygen species causing lipid peroxidation and cell necrosis.

• Incidence: 4.5–44 cases per 100,000 person-years (ranges vary by study); a large US insurance-claims study reported 7.1 per 100,000; another estimated 10.4 per 100,000 inhabitants.
• Incidence is increasing over the last three decades.
• Predominantly affects patients >60 years of age; the 70–79 age group has a relative risk 3.69× higher than the 50–59 group.
• Slight female predominance.
• About 20% of patients require operative intervention, usually emergent.
• Overall in-hospital mortality: ~12.7% (surgical cases: ~39.3%; medically managed: ~6.2%).

2. Causes & Risk Factors

Pathomechanisms

1. Non-occlusive (most common): Low-flow states — shock, sepsis, congestive heart failure, drugs, colon obstruction.
2. Occlusive vascular: Arterial thrombosis, embolism, or venous occlusion.
3. Postoperative: Following aortic (especially abdominal aortic aneurysm repair) or cardiac surgery — intraoperative cessation of blood flow, sacrifice of the IMA, or prolonged cross-clamp time.

During hypotension, splanchnic blood flow is preferentially redirected to the brain. At the histologic level, initial ischemic changes always begin in the mucosa on the antimesenteric side, then spread transmurally if the insult continues.

Risk Factors (Box 95.6, Sabiston)

• Septic shock, congestive heart failure, hemorrhagic shock, hypotension

• Ischemic heart disease, cerebrovascular disease, peripheral vascular disease

• Constipation, diarrhea, irritable bowel syndrome
• Obstructing lesions: volvulus, carcinoma, diverticulitis
• Fecal impaction

• Abdominal aortic aneurysm repair (highest risk)
• Cardiovascular surgery
• Endovascular abdominal interventions (chemoembolization)
• Post-colonoscopy (air insufflation raises intraluminal pressure)

• COPD, atrial fibrillation, hypertension

• Diabetes mellitus, dyslipidemia
• Systemic lupus erythematosus, rheumatoid arthritis

• Hypercoagulable states (thrombophilia)
• Sickle cell disease
• Long-distance running ("steal phenomenon" — exercise-induced splanchnic vasoconstriction)
• COVID-19 (recently identified association)

• Constipation-inducing drugs (opioids and non-opioids)
• Cocaine and methamphetamines
• Immunomodulatory drugs
• Oral contraceptives
• Triptans
• Angiotensin-converting enzyme inhibitors / angiotensin receptor blockers
• NSAIDs
• Chemotherapy agents (e.g., taxanes, bevacizumab)

Recurrent bouts occur in up to 15% of patients; smoking, COPD, and peripheral vascular disease predispose to recurrence.

3. Watershed Areas of the Colon

• Superior mesenteric artery (SMA): ileocolic, right colic, middle colic arteries → cecum, ascending colon, proximal 2/3 transverse colon
• Inferior mesenteric artery (IMA): left colic, sigmoid arteries, superior rectal artery → distal transverse colon, descending colon, sigmoid, upper rectum
• Internal iliac arteries: middle and inferior rectal arteries → rectum (hence rectum is relatively protected)

• Marginal artery of Drummond — runs parallel to the mesenteric margin from cecocolic to rectosigmoid junction; absent at the splenic flexure in up to 18–50% of individuals.
• Arc of Riolan (meandering mesenteric artery) — an inconsistent but critical collateral connecting SMA/middle colic to IMA/left colic at the mesenteric root; its presence often signals occlusion of one of the major trunks.

The Two Classic Watershed Areas

The rectum is infrequently affected because it receives dual blood supply from both the IMA (superior rectal) and the internal iliac arteries (middle and inferior rectal). Surgeons deliberately avoid anastomoses at the splenic flexure because the impaired blood supply risks anastomotic failure.

4. Clinical Features

Subtypes / Clinical Presentations

• Acute onset in elderly patients with or without predisposing factors
• Classic triad: crampy abdominal pain + urgent desire to defecate + passage of bright red or maroon blood per rectum (blood usually mixed with stool)
• Overall blood loss is small; transfusion rarely required
• Later: abdominal distension, ileus, nausea, vomiting
• Physical examination: tenderness or vague mass palpable along the affected colonic segment
• Peritoneal signs (transmural infarction) present in ~15% — accompanied by leukocytosis, metabolic acidosis, elevated lactate

• Milder, more transient form
• Common with drug-induced ischemia

• More chronic, indolent course
• Mild abdominal discomfort with intermittent diarrhea; blood may or may not be apparent
• Some patients are minimally symptomatic — discovered incidentally at endoscopy
• Risk of evolution to fibrotic stricture (may or may not cause obstructive symptoms)
• Systemic signs (fever, leukocytosis, bacteremia) signal risk of perforation → surgical resection indicated

• May involve the entire colon
• Systemically very ill patient
• Marked abdominal distension, leukocytosis, elevated lactate, metabolic acidosis
• High risk of transmural perforation and death

Key Clinical Pointers

• Left colon is more commonly affected than right colon; splenic flexure is most susceptible
• Rectum is typically spared (dual blood supply)
• Segmental distribution with normal-appearing colon proximal and distal to the affected segment
• Unlike AMI, pain is usually not out of proportion to physical findings (AMI presents with severe pain disproportionate to exam)

5. Investigations

Laboratory Tests

• CBC: Leukocytosis (elevated WBC correlates with severity)
• Metabolic panel: Metabolic acidosis (decreased bicarbonate), elevated BUN
• Lactate: Elevated — marker of severe ischemia; peak lactate >2.5 mmol/L predicts worse surgical outcome
• LDH: Elevated lactate dehydrogenase — associated with severe disease
• Albumin: Decreased in severe disease
• Haemoglobin: Decreased
• Stool studies: C. difficile toxin, ova & parasites, culture & sensitivity — to exclude infectious etiology

Plain Abdominal Radiograph (AXR)

• Abnormal in ~1/5 of patients
• "Thumbprinting" — rounded densities along the sides of gas-filled colon, representing submucosal edema (classic but non-specific)
• Bowel distension; air-fluid levels
• Free air → perforation → immediate surgery

CT Abdomen (Primary Imaging Modality)

CT angiography (multiphasic) should be performed in cases of severe pain out of proportion to findings or isolated right colon ischemia — to exclude proximal AMI (occlusion of ileocolic branch of SMA).

Colonoscopy (Gold Standard for Diagnosis)

• Should be performed within 48 hours of presentation
• Avoid in: acute peritonitis, suspected severe transmural ischemia (risk of perforation)
• Perform without or with minimal bowel preparation (left colon most affected — sigmoidoscopy often suffices in critically ill patients)
• Do not overinsufflate; do not advance scope beyond the most distal extent of disease

• Edematous, friable mucosa
• Erythema and petechial haemorrhage
• Mucosal ulceration
• "Single-stripe sign" — single linear ulcer running along the longitudinal colonic axis; rare but specific for IC
• Segmental distribution with abrupt transition between injured and normal mucosa
• Sparing of the rectum (supports ischemia over IBD)
• Severe cases: areas of gangrene (dark-blue/black mucosa)
• Biopsy: acute phase — crypt destruction, haemorrhage, capillary thrombosis; chronic phase — granulation tissue, atrophy, fibrosis

Endoscopy cannot reliably distinguish partial-thickness from full-thickness ischemia — clinical and CT correlation is essential.

Angiography

• Rarely indicated (IC is primarily a small-vessel disease; major trunks usually intact)
• Exception: concomitant AMI, isolated right-sided colitis, sudden-onset severe pain

MRI

• Alternative to CT; useful for grading severity; avoids radiation
• Less commonly used in acute presentations

6. Medical Management

General Supportive Measures

1. Bowel rest (nil by mouth)
2. IV fluid resuscitation — aggressive, especially in low-flow states; correct hypovolemia and hypotension
3. Nasogastric tube — if ileus is present
4. Optimise underlying conditions — heart failure, sepsis, arrhythmias, diabetes

Antibiotics

• Broad-spectrum antibiotics covering aerobic and anaerobic Gram-negative organisms — prescribed empirically because colonic ischemia disrupts the epithelial barrier, allowing bacterial translocation and sepsis
• Appropriate initial choice: piperacillin-tazobactam or a combination of a 3rd-generation cephalosporin + metronidazole

Vasoactive / Adjunct Therapies

• Phosphodiesterase type 5 (PDE5) inhibitors — may improve colonic blood flow
• Pentoxifylline — improves red blood cell deformability and microcirculatory flow
• Prostaglandin E1 — promotes mucosal healing

Cardiovascular Evaluation

• Evaluate for embolic source (arrhythmia, dilated cardiomyopathy) — may require anticoagulation
• Correct atrial fibrillation if present

Monitoring

• Serial abdominal examinations
• Repeat CT if clinical deterioration
• Early colonoscopy to confirm diagnosis and assess extent
• ICU-level monitoring in severe/complicated cases

Treatment of Complications

• Colonic stricture (chronic sequela): observation, endoscopic dilation, or surgical resection (depending on symptoms)
• Bleeding from ischemic ulcers: endoscopic haemostatic powder spray may be used for palliation

The decision to escalate to surgery is triggered by: peritonitis, deterioration despite 24–48 hours of medical management, massive bleeding, or imaging showing pneumatosis/portal venous gas.

7. Surgical Management

Indications for Emergency Surgery

• Peritonitis on physical examination
• Massive lower GI bleeding not controlled by other means
• Fulminant colitis with systemic deterioration
• Pneumatosis intestinalis or portal venous gas on imaging with clinical picture of IC
• Worsening clinical condition despite maximal medical management
• Free intraperitoneal air (perforation)

Operative Principles

• Remove all grossly ischemic colonic segments
• The serosa may appear normal even with transmural necrosis — so do not rely on serosal appearance alone
• Use intraoperative adjuncts to assess viability: Doppler ultrasonography, intraoperative colonoscopy, photoplethysmography
• A preoperative CT or endoscopic evaluation is critical to define extent of involvement

If ongoing ischemia is suspected after resection: leave fascia open, bowel in discontinuity → ICU for resuscitation → planned second-look laparotomy at 12–48 hours to assess viability and achieve definitive closure.

Indications for Elective Surgery (Sequelae)

• Symptomatic colonic stricture — after failed conservative management or dilation
• Ostomy reversal — after full recovery

Postoperative Course & Morbidity

• 2/3 of patients requiring surgery for severe IC develop medical complications: pneumonia, UTI, atrial fibrillation, myocardial infarction, acute renal failure, dialysis requirement
• 37% in-hospital mortality for severe IC requiring surgery

• Elderly age and poor functional status
• Multiple comorbidities
• Low-output heart failure (EF <20%)
• Preoperative septic shock
• Preoperative blood transfusions
• Preoperative acute renal failure
• Delay from admission to surgery
• Peak preoperative lactate >2.5 mmol/L
• Subtotal or total colectomy required
• Intraoperative catecholamine administration
• ASA class 4

8. Prognosis

Overall Outcomes

• Overall mortality: 12.7% (systematic review)
• Medically managed (mild-moderate disease): mortality ~6.2%
• Surgically managed: mortality ~39.3%
• Population-level overall mortality rate: 1.54 per 100,000 persons

Predictors of Poor Outcome

Additional Prognostic Considerations

• Right-sided IC carries a distinct presentation and worse outcome; some experts regard right- and left-sided IC as separate entities.
• Ischemic bowel disease predisposes to C. difficile infection among inpatients, which worsens mortality.
• Vascular and metabolic comorbidities significantly worsen outcomes.
• Recurrence occurs in up to 15% — particularly in patients with smoking, COPD, and peripheral vascular disease.

Sources

• Current Surgical Therapy, 14th Edition — Alsaad & Lipsett, Ischemic Colitis
• Sabiston Textbook of Surgery, The Biological Basis of Modern Surgical Practice — Chapter 95
• Yamada's Textbook of Gastroenterology, 7th Edition — Chapter 114, Ischemic Colitis
• Schwartz's Principles of Surgery, 11th Edition — Chapter on Ischemic Colitis

• Definition: IC as the most common GI ischemia, predominantly left-sided, splenic flexure most vulnerable
• Aetiology: Emphasises non-occlusive low-flow states, post-aortic surgery, drugs, and watershed anatomy (Griffiths' point, Sudeck's critical point)
• Clinical features: Classic triad of left iliac fossa pain, rectal bleeding, and diarrhoea; peritonitis in severe cases
• Investigations: AXR (thumbprinting), CT abdomen, flexible sigmoidoscopy/colonoscopy as gold standard
• Treatment: Majority conservative (IV fluids, bowel rest, antibiotics); surgery for peritonitis, perforation, or failed conservative management — Hartmann's procedure preferred for left-sided disease
• Prognosis: Most recover; stricture formation in ~10–15%; mortality high with transmural disease