A 75-year-old man with a past medical history of coronary artery disease, congestive heart failure, and atrial fibrillation presented with chronic postprandial abdominal pain and significant weight loss. His physical exam revealed a soft abdomen with normal bowel sounds and no tenderness to palpation. He underwent computed tomography angiography (CTA) of the abdomen, which demonstrated severe ostial stenoses of the celiac artery, superior mesenteric artery, and inferior mesenteric artery (Figure 37-1). Invasive digital subtraction angiography confirmed the diagnosis of chronic mesenteric ischemia. Given his age and significant comorbidities, the decision was made to proceed with endovascular revascularization as the primary approach. The patient underwent successful placement of 2 balloon-expandable stents in the celiac and superior mesenteric arteries (Figures 37-2 and 37-3). He was discharged home on the same day of the procedure and was asymptomatic on routine outpatient follow-up.

The mesenteric arterial system represents up to approximately 33% of the resting cardiac output. The mesenteric arterial vasculature includes the following major branches of the abdominal aorta: the celiac artery, the superior mesenteric artery (SMA), and the inferior mesenteric artery (IMA) (Figure 37-4).

CELIAC ARTERY

The first major branch of the abdominal aorta is the celiac artery, which usually arises at the level of the twelfth thoracic vertebra and courses anteriorly and slightly inferiorly. In the majority of patients, the celiac artery gives off the left gastric artery and then bifurcates into the splenic artery to the left and the common hepatic artery to the right. The common hepatic artery gives off the gastroduodenal artery inferiorly before continuing as the proper hepatic artery. The gastroduodenal artery gives off the superior pancreaticoduodenal artery.

The left gastric artery and its branches supply the lower esophagus and the stomach. The splenic artery and its branches supply the stomach, pancreas, and spleen. The gastroduodenal artery and its branches supply the stomach, pancreas, and the superior and descending portions of the duodenum. The proper hepatic artery and its branches supply the liver and stomach.

SUPERIOR MESENTERIC ARTERY

The second major branch of the abdominal aorta is the SMA, which typically arises at the level of the first lumbar vertebra, just inferior to the celiac trunk. It initially gives off the inferior pancreaticoduodenal artery to the right and then courses inferiorly to the right. Multiple jejunal arteries arise from the left surface of the SMA, followed by 8 to 12 ileal arteries. The middle colic artery arises from the right surface of the SMA, followed by the right colic artery. The SMA then terminates as the ileocolic artery. The middle colic artery divides into right and left branches, while the right colic artery divides into ascending and descending branches. The right branches of the middle colic artery anastomose with the ascending branches of the right colic artery.

The inferior pancreaticoduodenal artery and its branches ­supply the pancreas as well as the inferior and ascending portions of the duodenum. The right colic artery and its branches supply the ascending colon. The middle colic artery and its branches supply the proximal two-thirds of the transverse colon. The ileocolic artery and its branches supply the terminal ileum, cecum, and proximal ascending colon.

INFERIOR MESENTERIC ARTERY

The third major mesenteric artery is the IMA, which typically arises at the level of the third lumbar vertebra and courses inferiorly to the left. The IMA initially gives off the left colic artery, which divides into ascending and descending branches. The IMA then courses inferiorly to give off sigmoid arteries and terminates as the superior rectal artery.

While the ascending branch of the left colic artery supplies the distal third of the transverse colon and the superior portion of the descending colon, the descending branch of the left colic artery supplies the inferior portion of the descending colon. The sigmoid arteries supply the distal descending colon and the sigmoid colon. The superior rectal artery and its branches supply the rectum.

COLLATERAL CIRCULATION

The mesenteric arterial system has several interconnecting pathways that provide collateral circulation within the gastrointestinal system and protect the bowel from potential ischemia. For example, the pancreas and duodenum receive collateral circulation from the celiac artery and SMA through the anastomosis of the superior and inferior pancreaticoduodenal arteries. The entire colon receives collateral circulation from the SMA and IMA through the marginal artery of Drummond, which is a continuous arcade that runs along the colon and connects the terminal branches of the right, middle, and left colic arteries. In addition, the rectum receives collateral circulation from the IMA and internal iliac arteries through branches of the rectal arteries.

The splenic flexure of the colon is known as a watershed area because it does not have a primary source of arterial blood and relies on the dual blood supply from the most distal branches of the SMA and IMA through the marginal artery of Drummond. In the setting of splanchnic hypoperfusion, the splenic flexure is at increased risk of ischemia compared to other regions that have a primary source of arterial blood supply. Furthermore, Griffiths point, which is the site of communication between the ascending branch of the left colic artery and the marginal artery of ­Drummond at the splenic flexure, has been reported to be absent or tenuous in more than 50% of patients.¹ As a result, the splenic ­flexure of the colon is particularly at increased risk of ischemia.

EPIDEMIOLOGY

Acute mesenteric ischemia (AMI) is a vascular disease that results from an abrupt interruption of mesenteric perfusion, which leads to bowel ischemia and eventually bowel infarction if left untreated. The reported incidence of AMI is 1 per 1000 hospital admissions.² Despite the low incidence, AMI is a surgical emergency with a reported in-hospital mortality rate of about 75%.³ Given the high mortality rate, early diagnosis and treatment are critical in patients with AMI.

ETIOLOGY AND PATHOPHYSIOLOGY

AMI can be caused by arterial embolic occlusion in 40% to 50% of cases, arterial thrombotic occlusion of a previously stenotic vessel in 25% of cases, nonocclusive arterial disease in 20% of cases, venous thrombosis in 10% of cases, and vasculitis or dissection in less than 5% of cases.^4,5 Risk factors for AMI depend on the underlying etiology (Table 37-1).