Imaging Plays a Pivotal Role in Diagnosing Acute Mesenteric Ischemia

In concert with the RadioGraphics monograph, RSNA News shares the latest in emergency imaging.

Acute mesenteric ischemia (AMI) is a rare but very serious disease characterized by an abrupt decrease in blood supply to the bowel and nearby organs. If it’s not treated quickly, the consequences can be dire, resulting in cellular damage, bowel necrosis and death.

As with any type of end-organ ischemia, time is of the essence in AMI. Prompt recognition, diagnosis and treatment are essential for optimizing outcomes.

“Because clinical signs are often nonspecific and no reliable laboratory tests or biomarkers exist for early diagnosis, imaging—and CT angiography in particular—plays a critical role in the diagnosis, management and prognostication of AMI,” said Matthew Lee, MD, a radiologist at the University of Wisconsin School of Medicine and Public Health in Madison.

To fulfill this critical role, radiologists must be well-versed in the basic pathophysiology, imaging findings and associated prognosis of AMI. 

To help, Dr. Lee co-authored a RadioGraphics article providing a comprehensive overview on evaluating AMI via imaging. “Our goal is to equip radiologists with the tools they need to confidently identify AMI and, ultimately, improve patient outcomes,” he said.

Distinguishing Different Forms of AMI

Although CT angiography (CTA) is the imaging study of choice for AMI, Dr. Lee noted that many imaging features, including decreased bowel wall enhancement, bowel thinning and dilatation, and arterial occlusion, can be identified on routine portal venous phase CT.

However, what makes diagnosing AMI so challenging is that it’s not just a single disease, but a group of different conditions. Each type has its own unique pathophysiology, clinical presentation, imaging features and prognosis.

“Although all forms of AMI can lead to irreversible transmural bowel necrosis (TBN), their imaging findings must be interpreted in the context of the underlying cause,” Dr. Lee said.

Confusion often arises because of the rarity of AMI and the tendency for these entities and their imaging characteristics to be conflated, according to Dr. Lee.

Mesenteric findings, such as fat stranding and fluid, are uncommon early in arterial occlusive AMI compared to non-occlusive mesenteric ischemia (NOMI) or strangulating small bowel obstruction. Dr. Lee said the absence of mesenteric findings are an important pertinent negative in early or non-transmural arterial occlusive ischemia.

In contrast, bowel wall thickening, mesenteric stranding and fluid are common in venous ischemia. “When wall thickening is seen in arterial occlusive AMI, it is more likely related to reperfusion injury, such as can be seen following endovascular revascularization,” Dr. Lee noted.

Pneumatosis, or the abnormal presence of gas within the bowel wall, is another important imaging finding. It can be confusing because it’s seen in both life-threatening ischemia and a range of benign conditions.

“Bandlike pneumatosis and the combination of pneumatosis and portal venous gas are highly associated with TBN,” Dr. Lee explained. “Consequently, pneumatosis should not be interpreted in isolation but be evaluated within the context of accompanying imaging, clinical and laboratory findings.”