What is the differential diagnosis (DDX) of non-specific intestinal necrosis (NSIN) on computed tomography (CT) scan?

Differential Diagnosis of Non-Specific Intestinal Necrosis (NSIN) on CT Scan

When CT demonstrates intestinal necrosis without a clear etiology, the differential diagnosis must prioritize mesenteric ischemia (both occlusive and non-occlusive), followed by infectious/inflammatory enterocolitis, and less commonly radiation enteritis, drug-induced injury, or vasculitis. 1, 2, 3

Primary Differential Considerations

1. Mesenteric Ischemia (Most Critical)

Arterial Occlusive Disease:

• Superior mesenteric artery (SMA) embolism or thrombosis is the most common cause of intestinal necrosis requiring immediate intervention 1, 2
• CT findings include vessel occlusion, reduced bowel wall enhancement, pneumatosis intestinalis, and portal venous gas 1, 2
• CTA is the diagnostic modality of choice to identify arterial compromise 1, 2

Non-Occlusive Mesenteric Ischemia (NOMI):

• Occurs in critically ill patients with low-flow states, particularly those on vasopressors 2, 4
• CT may show bowel wall thinning, decreased enhancement, and mesenteric vessel narrowing without occlusion 2, 4
• Mortality exceeds 50-70% even with treatment 2, 5
• Plasma I-FABP >3114 pg/mL has 90% positive predictive value for intestinal necrosis 4

Mesenteric Venous Thrombosis:

• Less common cause but presents with bowel wall thickening, mesenteric stranding, and venous filling defects 2
• May have more indolent presentation than arterial occlusion 2

2. Infectious Enterocolitis

Clostridium difficile Colitis:

• Can cause severe pancolitis with necrosis, particularly in immunocompromised patients 1, 3
• "Giraffe coat" sign on CT (accordion-like pattern of thickened haustral folds) is relatively specific 3
• Preferentially affects the colon with marked wall thickening and pericolonic stranding 3

Cytomegalovirus (CMV) Enterocolitis:

• Occurs in immunocompromised patients (HIV, transplant recipients, IBD patients on immunosuppression) 1, 6
• CT shows variable findings from patchy erythema to deep ulcers and pseudotumors 1
• Can mimic Crohn's disease with discontinuous involvement 1

Other Bacterial Infections:

• Salmonella, Shigella, Campylobacter can cause severe colitis mimicking ulcerative colitis 1, 3
• Yersinia enterocolitis can resemble Crohn's disease with terminal ileal involvement 1
• Intestinal tuberculosis affects terminal ileum/ileocecal region in 50% of cases, particularly in immunocompromised patients 1

3. Inflammatory Bowel Disease Complications

Crohn's Disease with Stricture and Ischemia:

• Strictures defined as luminal narrowing with upstream dilation >3-4 cm 1
• Can progress to penetrating complications (fistula, abscess) or ischemic necrosis 1
• Look for asymmetric wall thickening, mesenteric fat stranding, and engorged vasa recta 1

Severe Ulcerative Colitis:

• Continuous colonic involvement with rectal sparing rare 1
• Toxic megacolon can lead to perforation and necrosis 1

4. Drug-Induced and Toxic Causes

NSAID Enteropathy:

• Can cause ulceration and strictures throughout small bowel 1, 3
• Often presents with non-specific inflammation and potential perforation 1

Radiation Enteritis:

• History of pelvic or abdominal radiation therapy is key 3, 6
• Affects bowel segments within radiation field with wall thickening and strictures 3, 6

Graft-Versus-Host Disease:

• Occurs in bone marrow transplant recipients 3, 6
• Diffuse small bowel involvement with wall thickening and mucosal sloughing 3, 6

5. Vasculitis and Infiltrative Disorders

Behçet Disease:

• Can cause intestinal ulceration and necrosis 6
• Look for multisystem involvement and oral/genital ulcers clinically 6

Amyloidosis:

• Infiltrative process causing wall thickening and potential ischemia 6
• Rare cause but consider in patients with systemic amyloidosis 6

Critical Diagnostic Approach

Immediate Assessment:

• Obtain CTA abdomen/pelvis if not already performed to evaluate vascular patency and identify active bleeding 1, 2
• Look for pneumatosis intestinalis and portal venous gas (indicate transmural necrosis) 1, 2
• Assess bowel wall enhancement pattern: absent enhancement = necrosis 1, 2

Clinical Context Integration:

• Age >60 years, atrial fibrillation, recent MI = embolic arterial occlusion 1, 2
• ICU patient on vasopressors = NOMI 2, 4
• Immunocompromised state = infectious causes (CMV, TB, fungal) 1
• Recent antibiotics = C. difficile colitis 1, 3
• IBD history = disease complication or superimposed infection 1

Distribution Pattern Analysis:

• SMA territory (jejunum to mid-transverse colon) = arterial occlusion 1, 2
• Watershed areas (splenic flexure, rectosigmoid) = low-flow ischemia 1
• Pancolitis = C. difficile, severe UC, or ischemic colitis 1, 3
• Terminal ileum/ileocecal = Crohn's, TB, Yersinia 1

Common Pitfalls to Avoid

• Do not delay surgical consultation while pursuing additional imaging if peritoneal signs are present 1, 2
• Do not assume normal lactate excludes mesenteric ischemia - lactate elevation is a late finding 1, 5
• Do not rely on standard CT with contrast alone - CTA with arterial phase is essential for vascular assessment 1, 2
• Do not overlook NOMI in critically ill patients - conventional angiography may be needed for diagnosis and treatment 2
• Serial examinations are mandatory when observation is chosen, as peritoneal signs may take hours to develop 1