INTRODUCTION

Mesenteric ischemia is caused by a reduction in intestinal blood flow, which most commonly arises from occlusion, vasospasm, and/or hypoperfusion of the mesenteric vasculature. The clinical consequences can be catastrophic, including sepsis, bowel infarction, and death, making rapid diagnosis and treatment imperative.

Although uncommon in the general population, ischemic colitis is the most frequent form of mesenteric ischemia, affecting mostly the elderly [1]. The majority of patients (85 percent) develop non-gangrenous ischemia, which is usually transient and resolves without sequelae [2]. Only a minority of these patients develop long-term complications, which include persistent segmental colitis and the development of a stricture. On the other hand, approximately 15 percent of patients with colonic ischemia develop gangrene, the consequences of which are life-threatening.

Colonic ischemia has been described in a number of clinical settings (table 1), although it often develops insidiously and no specific cause can be identified. The diagnosis and treatment of patients can be challenging since it often occurs in patients who are debilitated and have multiple medical problems.

This topic review will focus on the pathogenesis, clinical manifestations, diagnosis, and treatment of colonic ischemia. Acute and chronic mesenteric ischemia are discussed separately. (See "Acute mesenteric ischemia" and "Chronic mesenteric ischemia".) A guideline on this topic has also been issued by the American Gastroenterological Association (AGA) (http://www.gastro.org/practice/medical-position-statements) [3].

BLOOD SUPPLY OF THE COLON

The colon has a specific vascular arrangement except for rare individual anatomic variations (figure 1) [4]. The superior mesenteric artery (SMA) and inferior mesenteric artery (IMA) both supply blood to the colon. The SMA arises from the aorta, about 1 cm below the celiac axis at the level of L1 or L2. It supplies the entire small intestine except for the superior part of the duodenum. The SMA has four main branches: the inferior pancreaticoduodenal, middle colic, right colic, and the ileocolic arteries. As a general rule, the ileocolic artery supplies the terminal ileum, cecum, appendix, and proximal ascending colon while a portion of the ascending colon and hepatic flexure receive blood from the right colic artery. The middle colic artery supplies the proximal transverse colon.