1. Acute mesenteric ischemia
Visceral arterial embolism presents acutely with severe abdominal pain. In contrast, patients with primary visceral arterial thrombosis often give an antecedent history consistent with chronic mesenteric ischemia. The key finding with acute mesenteric ischemia is severe, steady, diffuse abdominal pain with an absence of focal tenderness or distention. This “pain out of proportion” to physical examination findings occurs because ischemia initially is mucosal and does not impact the peritoneum until transmural ischemia inflames the peritoneal lining. A high white blood cell count, lactic acidosis, hypotension, and abdominal distention may aid in the diagnosis.
2. Chronic mesenteric ischemia
Patients are generally over 45 years of age and may have evidence of atherosclerosis in other vascular beds. Symptoms consist of epigastric or periumbilical postprandial pain lasting 1–3 hours. To avoid the pain, patients limit food intake and may develop a fear of eating. Weight loss is universal.
Characteristic symptoms are left lower quadrant pain and tenderness, abdominal cramping, and mild diarrhea. Rectal discharge will appear mucus-like or bloody and should prompt further evaluation.
B. Imaging and Colonoscopy
Contrast-enhanced CT is highly accurate at determining the presence of ischemic intestine. In patients with acute or chronic mesenteric ischemia, a CTA or MRA can demonstrate narrowing of the proximal visceral vessels. In acute mesenteric ischemia from a nonocclusive low flow state, angiography is needed to display the typical “pruned tree” appearance of the distal visceral vascular bed (eFigure 12–9). Ultrasound scanning of the mesenteric vessels may show proximal obstructing lesions.
A: Preoperative visceral arteriogram showing severe stenosis of the celiac and superior mesenteric arteries. B: The postoperative visceral arteriogram shows wide patency of the celiac and superior mesenteric arteries after transaortic endarterectomy. The inset shows the atherosclerotic stenotic lesions removed by endarterectomy. (Reproduced, with permission, from Way LW [editor]. Current Surgical Diagnosis & Treatment, 10th ed. Originally published by Appleton & Lange. Copyright © 1994 by The McGraw-Hill Companies, Inc.)
In patients with ischemic colitis, flexible sigmoidoscopy should be performed to assess the grade of ischemia that occurs most often in watershed areas, such as the rectal sigmoid and splenic flexure.