Imaging in Intestinal Ischemic Disorders
Section snippets
Epidemiology
Vascular compromise of the gut is responsible for approximately 0.1% of all hospital admissions and 1.0% of admissions for an acute abdomen. The diagnosis of this disorder is on the increase for several reasons. MI and infarction occur predominantly in the geriatric population with comorbid cardiovascular disease and other systemic dysfunction. The population is aging, and the number of cases of MI is expected to increase dramatically as the “Baby Boom” generation comes of age. Other factors
Intestinal vascular anatomy
Knowledge of mesenteric vascular anatomy and physiology is key to an appreciation of the causes and consequences of intestinal ischemia and infarction. The anatomy of the mesenteric circulation is complicated by the almost endless variations of blood supply to the gut.
Physiology of the mesenteric circulation
In the fasting state, the mesenteric vessels receive approximately 20% to 25% of the cardiac output and the splanchnic circulation contains approximately one third of the total blood volume, which makes it the circulatory system's largest reservoir. Approximately 25% of the splanchnic circulation flows directly to the liver by way of the hepatic artery, and the remaining 75% of blood flow reaches the liver by way of the portal venous system.12, 16
At rest, approximately 70% to 80% of the blood
Classification of ischemic bowel disease
Intestinal ischemic disorders have been classified into several major types:17, 18, 19
AMI
SMAE
NOMI
Superior mesenteric artery thrombosis
Superior mesenteric vein thrombosis
CMI (intestinal angina)
CI
Reversible ischemic colopathy
Transient ulcerating ischemic colitis
Chronic ulcerating ischemic colitis
Colonic stricture
Colonic gangrene
Fulminant universal ischemic colitis
CI is the most common vascular disorder of the gut, followed by AMI. AMI is associated with compromise of the blood flow in the SMA
Small Bowel
Pathologic evidence of small bowel ischemia and infarction (Fig. 6, Fig. 7, Fig. 8) may be diffuse and confluent or patchy and multifocal. The serosal aspect of the affected small bowel often appears congested or blue and black. Perforations may be present but may not be accompanied by well-developed fibrinous exudates if the surgical resection occurs within a short time of presentation. The mesentery is usually pale in arterial occlusions and congested and hemorrhagic in venous thrombosis. The
Clinical features of mesenteric ischemia
To date, no reliable physiologic or biochemical means of detecting MI and predicting behavior have been established. Serum lactate is an established marker of cell hypoxia but lactic acidosis is often a late finding in the diagnostic pathway with concomitant shock, bowel necrosis, and circulatory collapse.22, 26
Recently, plasma D-dimer levels have been suggested as an early marker of acute ischemia. In animal studies, they have been shown to correlate with the onset of ischemia and function as
Plain Abdominal Radiographs
Most patients who have intestinal ischemia demonstrate nonspecific findings, such as intestinal dilatation (see Fig. 12), gasless abdomen, a small bowel pseudo-obstruction pattern, or paralytic ileus. More specific but far less common findings include thumbprinting in which multiple, round, smooth soft tissue densities project into the intestinal lumen because of mucosal and submucosal edema and hemorrhage. Specific late signs indicating infarction include pneumatosis intestinalis (PI; see
Acute arterial and venous mesenteric ischemia
The clinical setting of AMI is characterized by the combination of a difficult diagnosis, high fatality rates, and the need for rapid and aggressive diagnostic and therapeutic interventions in patients who are often elderly and have multiple comorbidities.26
There are four main categories of AMI: SMAE (50%), NOMI (20%–30%), SMAT (15%–25%), and superior mesenteric vein thrombosis (SMVT) (5%).1, 2, 3
Chronic mesenteric ischemia
Atherosclerosis of the mesenteric circulation is quite common, particularly in the elderly population. Symptomatic CMI, however, is rare because of the development of extensive collaterals. Risk factors for the development of CMI include a positive family history, smoking, hypertension, and hypercholesterolemia, the same risk factors as for atherosclerosis. There is a female predominance of symptomatic disease.
Nonatherosclerotic causes of CMI are less frequent and include celiac artery
Colonic ischemia
CI is the most common vascular disorder of the gut in elderly patients. The colon is predisposed to ischemia because of the fact that it receives less blood flow per gram of tissue than does the remainder of the gastrointestinal tract.28, 29 Indeed, there is an extensive network of intramural vessels arising from the vasa recta and vasa brevia in the mesenteric border of the gut that gives rise to a microvascular plexus in the muscularis propria and submucosal layer and is less well developed
Pneumatosis intestinalis
Intramural gas is associated with several disorders ranging from life-threatening to benign.82 PI pathogenically derives from four major categories: bowel necrosis, mucosal disruption, increased mucosal permeability, and pulmonary disease.83 The first three causes may be found in patients who have intestinal ischemia (see Fig. 13, Fig. 14, Fig. 1520, and 21). In patients who have intestinal ischemia, gas may dissect from the intestinal lumen because of an increase in intraluminal pressure (eg,
Focal segmental mesenteric ischemia
Short-segment ischemic disease may be caused by a large number of disorders, including vasculitis, medications, surgery, radiation, neoplasm, and, most importantly, bowel obstruction. Most cases of localized MI show similar radiologic features. It is important, however, to determine the underlying cause to guide diagnostic and therapeutic planning. The clinical presentation of localized MI depends on the length and distribution of the ischemia and the course of disease.30, 33
With the exception
Therapeutic options
Patients who are suspected of having AMI require volume resuscitation; correction of hypotension, congestive heart failure, and cardiac arrhythmias; correction of acid-base and electrolyte abnormalities; and infusion of broad-spectrum antibiotics offering theoretic protection against the bacterial translocation that accompanies loss of mural integrity.26 Specific therapies are discussed next.
Summary
Gastrointestinal tract ischemia can threaten bowel viability with potentially catastrophic consequences, including intestinal necrosis and gangrene. Because presenting symptoms and signs are relatively nonspecific and imaging findings may be confusing, the diagnosis of intestinal tract ischemia requires a high index of suspicion. It is important to attempt to determine the cause of the intestinal ischemia and differentiate between intestinal ischemia and infarction. The early inclusion of bowel
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2015, Radiologic Clinics of North AmericaCitation Excerpt :The splenic flexure is particularly sensitive to ischemia because it lies at Griffin point, the watershed between the middle colic and left colic artery blood supply.20 Colonic ischemia (CI) is divided into 6 categories that reflect pathologic changes and clinical severity: milder forms, such as reversible ischemic colopathy and transient ulcerating IC; severe forms, such as colonic gangrene and fulminant universal IC; and chronic forms, including colonic stricture and chronic ulcerating IC.98 The clinical course of the disease can take 2 forms, a mild self-limited form that resolves in approximately 2 weeks in about half of patients and a fulminant form with gangrenous ischemia with a greater than 50% mortality rate.98–100