What is the best diagnostic approach for ischemic colitis, using methods such as colonoscopy (Colonoscopy), computed tomography (CT), or computed tomography with angiography (CT with angiography)?

Diagnosis of Ischemic Colitis

For suspected ischemic colitis, CT with intravenous contrast is the initial imaging modality of choice, followed by colonoscopy within 48 hours to confirm the diagnosis endoscopically and histologically. 1, 2, 3

Initial Diagnostic Approach

CT with Intravenous Contrast (First-Line)

• CT abdomen/pelvis with IV contrast should be performed immediately when ischemic colitis is suspected, as it can support clinical diagnosis, define severity and distribution of ischemia, and has prognostic value. 1, 2, 3
• CT detects bowel wall thickening, abnormal wall enhancement (decreased or increased), mesenteric edema, pneumatosis, and portal venous gas—all signs of ischemia. 4, 1
• CT has a sensitivity and specificity of 95-100% for detecting vascular abnormalities and can accurately exclude other causes of abdominal pain. 1, 2
• A triple-phase study (non-contrast, arterial, and portal venous phases) is important for identifying the underlying cause and evaluating for bowel complications. 1, 2

CT Angiography Considerations

• CT angiography is specifically indicated when mesenteric arterial ischemia (acute mesenteric ischemia) is suspected, not typical ischemic colitis. 1, 2
• For isolated colonic ischemia (ischemic colitis), standard CT with IV contrast is sufficient and preferred over CTA. 3
• CTA is reserved for cases where there is clinical suspicion of superior mesenteric artery or inferior mesenteric artery occlusion, or when differentiating from acute mesenteric ischemia. 1, 2

Colonoscopy (Essential for Confirmation)

Timing and Indications

• Colonoscopy should be performed within 48 hours in all but fulminant cases to reach the distal-most extent of disease and provide endoscopic and histological confirmation. 3
• Colonoscopy is considered the gold standard for diagnosing ischemic colitis, with approximately 95% of patients having inflammation visible in the left colon. 4, 5, 6
• The procedure should extend to the distal-most extent of disease to fully characterize distribution and severity. 3

Endoscopic Findings

• Look for mucosal edema, erythema, friability, ulcerations, and in severe cases, necrotic mucosa or pseudomembranes. 3, 6
• Biopsies should be obtained for histological confirmation, which typically shows mucosal necrosis, hemorrhage, and inflammatory infiltrate. 3, 6
• Endoscopic severity correlates with clinical outcomes and need for surgical intervention. 3

Clinical Pitfalls and Caveats

When to Suspect Gangrenous vs. Nongangrenous Disease

• Peritoneal signs (rebound tenderness, guarding) indicate gangrenous ischemia requiring urgent surgery—do not delay for colonoscopy in these patients. 1, 3
• Laboratory markers suggesting gangrenous disease include marked leukocytosis, elevated lactate, metabolic acidosis (low bicarbonate, low pH), and elevated D-dimer. 1, 2
• CT findings of pneumatosis, portal venous gas, or lack of bowel wall enhancement suggest transmural infarction and mandate immediate surgical consultation. 4, 1, 3

ICU and Critically Ill Patients

• Ischemic colitis is often under-diagnosed in ICU patients due to nonspecific symptoms, sedation, and ventilation masking characteristic features. 5
• Bedside colonoscopy and diagnostic laparoscopy are reliable options for diagnosing ischemic colitis in critically ill patients who cannot be transported. 5

Plain Radiography Has No Role

• Plain abdominal radiographs have limited diagnostic value and should not be relied upon—25% of patients with acute mesenteric ischemia have normal radiographs. 2
• Plain films may show nonspecific findings like bowel dilation or thumbprinting, but these are neither sensitive nor specific. 6

Algorithmic Approach

1. Clinical suspicion (abdominal pain, bloody diarrhea, risk factors like age >60, cardiovascular disease, hypotension)
2. Immediate CT abdomen/pelvis with IV contrast to assess for ischemia, rule out complications, and exclude other diagnoses 1, 2, 3
3. If peritoneal signs present: Urgent surgical consultation—do not proceed to colonoscopy 1, 3
4. If no peritoneal signs: Colonoscopy within 48 hours for endoscopic and histological confirmation 3
5. If CT shows arterial occlusion or clinical picture suggests acute mesenteric ischemia: Consider CT angiography or conventional angiography 1, 2

Management Implications Based on Diagnosis

• Most cases (80-85%) are nongangrenous and resolve with conservative management: bowel rest, IV fluids, broad-spectrum antibiotics, and correction of precipitating factors. 3, 6, 7
• Gangrenous ischemic colitis (15-20% of cases) requires urgent operative intervention with high morbidity and mortality. 6, 7, 8
• Specific CT and endoscopic features (pneumatosis, portal venous gas, transmural necrosis) correlate with need for surgery and worse outcomes. 3, 8