What is the difference in presentation between acute and chronic mesenteric ischemia? How is this difference explained by the underlying pathophysiology?
Acute mesenteric ischemia (AMI) typically presents with sudden-onset abdominal pain. The pain is classically “out of proportion to findings on physical exam,” because early in the presentation of AMI the patient may have a normal abdominal exam. AMI is caused by hypoperfusion of the small intestine, which can be due to embolization, thrombosis, or nonocclusive mesenteric ischemia (NOMI) due to low flow to the superior mesenteric artery or celiac artery. Acute mesenteric vein thrombosis causes a similar presentation.
Unlike AMI, chronic mesenteric ischemia may be asymptomatic or have an insidious onset. Patients often note recurrent episodes of pain during the first hour after eating, which typically subsides over the course of several hours. Patient may therefore develop sitophobia , meaning fear of eating, and present with weight loss and nutritional deficiencies. Symptoms often are progressive. With a careful history, patients who present with AMI often give a history consistent with chronic mesenteric ischemia. This disorder is classically associated with occlusion of two of three major braches from the aorta that feed the intestinal tract: celiac, superior, and inferior mesenteric arteries.