Intestinal Ischemia

1

What is the arterial supply to the gut?

The foregut (stomach and duodenum) receives its blood supply from the celiac artery, the midgut (jejunum to the proximal descending colon) from the superior mesenteric artery (SMA), and the hindgut (the remainder of the intraperitoneal gut) from the inferior mesenteric artery (IMA).

2

Name the potential collateral pathways between the celiac axis and SMA, SMA and IMA, and Iliac and IMA

The pancreaticoduodenal arteries form the major collaterals between the celiac artery and the SMA. The gastroduodenal artery gives off the superior pancreaticoduodenal artery that encircles the head of the pancreas and anastomoses with the inferior pancreaticoduodenal artery, the first branch of the SMA.

The SMA and IMA have two main connections. The marginal artery of Drummond lies within the mesentery of the colon and is made up of branches of the ileocolic, right, middle, and left colic arteries. The arc of Riolan (meandering mesenteric artery) is more central and connects the middle colic branch of the SMA and the left colic branch of the IMA.

The internal iliac artery gives rise to the middle rectal artery, which can provide flow to the superior rectal and thus the IMA.

3

For extra credit, for whom is the marginal artery of Drummond named? What about the arc of Riolan?

Hamilton Drummond, a British surgeon, proved the anastomotic connection that bears his name by ligating the origins of the right, middle, and left colic arteries and demonstrating flow to the sigmoidal arteries in 1913 and 1914.

Jean Riolan (1577–1657) was a well-known French anatomist who (ironically) opposed Harvey’s theory of circulation but is acknowledged to be the first person to point out the communication between the SMA and IMA.

4

Name the common causes of acute intestinal ischemia

Acute SMA embolism (50% of all cases), acute SMA thrombosis, nonocclusive mesenteric ischemia (NOMI), mesenteric venous thrombosis, vasculitis, and iatrogenic causes (e.g., inotropic agents, aortic surgery).

5

What is the mortality rate of patients with acute mesenteric ischemia?

Although the prognosis of embolic occlusion is somewhat better because of the dramatic presentation, the diagnosis of acute mesenteric ischemia is often made after infarction. The result is a high mortality rate (60%–80%), regardless of cause. Despite advances in diagnosis, intervention, and critical care, this figure has gone largely unchanged for more than 50 years.

6

What is a paradoxical embolus?

A paradoxical embolus occurs in the setting of a venous thrombus embolizing to the arterial circulation via a cardiac defect (typically, an atrial septal defect allowing right-to-left shunting).

7

What is the diagnostic triad of acute embolic intestinal ischemia?

Sudden onset of (1) severe abdominal pain, (2) bowel evacuation (vomiting or diarrhea), and (3) a history of cardiac disease (source for arterial emboli). An additional hallmark is pain out of proportion to physical findings.

8

How does the presentation of patients with acute thrombotic occlusion differ?

Thrombotic occlusion typically presents in elderly patients with diffuse atherosclerotic occlusive disease or in patients with a history consistent with chronic mesenteric ischemia (see question 24 ). Particularly in the former group of patients, acute embolic occlusion may be indistinguishable from thrombotic occlusion.

9

Which laboratory value is diagnostic of acute intestinal ischemia? Is acidosis?

No laboratory values are diagnostic for acute intestinal ischemia. Metabolic acidosis is a late finding and implies advanced ischemia or infarction. Similarly, elevated lactate and elevated phosphate levels are nonspecific and frequently late findings. Although profound leukocytosis is found in the majority of patients, no laboratory studies are specific. The diagnosis is pursued on clinical suspicion alone.

10

When acute intestinal ischemia is suspected, what study is diagnostic?

Computed tomography angiography (CTA) of the abdomen is diagnostic. It is helpful to review reconstructed sagittal views of the aorta to visualize the visceral vessels. CTA has the distinct advantages of speed, accessibility, and evaluation of the bowel in addition to other sources in the differential diagnosis of acute abdominal pain.

11