CELIAC AXIS

The CA (Fig. 114-1) arises from the anterior aorta and typically gives rise to three major branches: the left gastric artery, the common hepatic artery, and the splenic artery. The common hepatic artery gives rise to the gastroduodenal, right gastroepiploic, and anterior superior pancreaticoduodenal arterial branches. The splenic artery gives off pancreatic and left gastroepiploic arterial branches. The CA and its branches supply the stomach, duodenum, pancreas, and liver.

Figure 114-1. Diagram of typical celiac axis (CA) anatomy and its anastomoses with the superior mesenteric artery (SMA). A, aorta; AIPD, anterior inferior pancreaticoduodenal artery; ASPD, anterior superior pancreaticoduodenal artery; CP, caudal pancreatic artery; DP, dorsal pancreatic artery; GD, gastroduodenal artery; H, common hepatic artery; LG, left gastric artery; PIPD, posterior inferior pancreaticoduodenal artery; PM, pancreata magna; RGE, right gastroepiploic artery; S, splenic artery; TP, transverse pancreatic artery.

(From Nebesar RA, Kornblith PL, Pollard JJ, Michels NA. Celiac and superior mesenteric arteries: a correlation of angiograms and dissections. Boston: Little, Brown; 1969.)

SUPERIOR MESENTERIC ARTERY

The SMA (Fig. 114-2) has its origin from the anterior aorta near the neck of the pancreas. It gives rise to five major vessels: the anterior and posterior inferior pancreaticoduodenal vessels, middle colic, right colic, and ileocolic arteries, as well as to a series of jejunal and ileal branches, all of which supply their named portions of intestine. These intestinal branches typically form a series of arcades, and from the terminal arcade, numerous straight vessels arise that enter the intestinal wall.

Figure 114-2. Diagram of typical superior mesenteric artery (SMA) anatomy. AIPD, anterior inferior pancreaticoduodenal artery; COL, colic branches; IL, ileal branches; IC, ileocolic artery; JEJ, jejunal branches; MC, middle colic artery; PIPD, posterior inferior pancreaticoduodenal artery; RC, right colic artery.

(From Nebesar RA, Kornblith PL, Pollard JJ, Michels NA. Celiac and superior mesenteric arteries: a correlation of angiograms and dissections. Boston: Little, Brown; 1969.)

INFERIOR MESENTERIC ARTERY

The IMA (Fig. 114-3) arises 3 to 4 cm above the aortic bifurcation close to the inferior border of the duodenum. It branches into the left colic artery, gives off multiple sigmoid branches, and terminates as the superior rectal artery. The IMA and its branches supply the large intestine from the distal transverse colon to the proximal rectum. The distal rectum is supplied by branches of the internal iliac (hypogastric) artery.

Figure 114-3. Diagram of typical inferior mesenteric artery (IMA) anatomy and its anastomoses with the superior mesenteric artery (SMA). AOR, arc of Riolan; ASC, ascending branch of the left colic artery; CA, central artery; DSC, descending branch of the left colic artery; LMC, left branch of middle colic artery; MA, marginal artery; MC, middle colic artery; RMC, right branch of middle colic artery; S, sigmoid branches; SR, superior rectal artery.

(From Nebesar RA, Kornblith PL, Pollard JJ, Michels NA. Celiac and superior mesenteric arteries: a correlation of angiograms and dissections. Boston: Little, Brown; 1969.)

COLLATERAL AND ANASTOMOTIC CIRCULATION

Abundant collateral circulation to the stomach, duodenum, and rectum accounts for the paucity of ischemic events in these areas. The major anastomosis between the CA and the SMA is formed from the superior pancreaticoduodenal branch of the CA and the inferior pancreaticoduodenal branch of the SMA. These vessels constitute the pancreaticoduodenal arcade and provide blood to the duodenum and the pancreas. The splenic flexure and sigmoid colon have limited anastomoses, and ischemic damage is more common in these locations.

There are three potential paths of communication between the SMA and IMA: the marginal artery of Drummond, which is closest to and parallel with the wall of the intestine; the central anastomotic artery, a larger and more centrally placed vessel; and the arc of Riolan, an artery in the base of the mesentery. In the presence of SMA or IMA occlusion, a large collateral termed the meandering artery may be identified angiographically and represents a dilated central anastomotic artery or arc of Riolan (Fig. 114-4). It is critical to determine the direction of flow within a meandering artery before sacrificing the IMA, such as during aortic aneurysm surgery, lest the IMA be the main vessel supplying blood to the small bowel because of an occluded SMA.

Figure 114-4. Film from a flush aortogram of a patient with superior mesenteric artery (SMA) occlusion. The presence of a prominent meandering artery indicates that the collateral channels have been present for some time and that the occlusion is not acute. The arrows show the direction of flow from the inferior mesenteric artery to the SMA.

(From Boley SJ, Brandt LJ, Veith FJ. Ischemic disorders of the intestines. Curr Probl Surg 1978; 15:29.)

INCIDENCE

AMI accounts for about 0.1% of admissions to our tertiary care center. This figure has risen since the early 1980s owing to increased recognition of the disorder, an aging population, and the widespread use of intensive care units with the salvage of patients who previously would have died from cardiovascular conditions but who now survive to develop AMI as a delayed consequence of their primary disease.

Most series of AMI reported in the late 1970s and early 1980s showed that SMAE was responsible for 40% to 50%, NOMI for 20% to 30%, and SMAT for 10% to 20% of cases. The incidence of NOMI has now declined, however, likely because intensive care unit monitoring enables prompt correction of hypotension and blood volume deficits, and the widespread use of calcium channel blockers and other systemic vasodilators might protect the vascular bed from spasm. Today, SMAE is the most common cause of AMI. In one study of autopsies on patients who died from acute mesenteric thromboembolic occlusion the embolus-to-thrombus ratio was 1.4 : 1.⁴

CLINICAL FEATURES

Early identification of AMI requires a high index of suspicion, especially in patients older than 50 years who have long-standing congestive heart failure (particularly if the heart failure is poorly controlled), cardiac arrhythmias, recent myocardial infarction, or hypotension. The development of sudden abdominal pain in a patient with any of these risk factors should suggest the diagnosis of AMI. Younger patients, however, are not without risk of AMI, especially if they are taking vasoactive medications (e.g., phenylephrine, amphetamines, triptans), are using cocaine, or have underlying thrombophilia. Hence, unexplained, persistent, and severe abdominal pain should prompt consideration of AMI as an explanation for the pain. A history of postprandial abdominal pain in the weeks to months preceding the acute onset of severe abdominal pain is associated only with SMAT.

Almost all patients with AMI have acute abdominal pain. Early in the course of disease, the pain of AMI is far more impressive than the physical findings. Initially, the pain is severe, but the abdomen usually is flat, soft, and most often not tender, or it is less tender than expected based on the magnitude of the pain. Sudden, severe abdominal pain accompanied by rapid and often forceful bowel evacuation, especially with minimal or no abdominal signs, strongly suggests SMAE. A more indolent and less striking onset is more typical of MVT, whereas with NOMI, appreciation of abdominal pain may be overshadowed by the precipitating disorders, such as hypotension, acute congestive heart failure, acute hypovolemia, or cardiac arrhythmias. Pain is absent in as many as 25% of patients with NOMI.

Unexplained abdominal distention or gastrointestinal bleeding may be the only indications of AMI when pain is absent, especially when AMI is due to NOMI. Distention, although absent early in the course of AMI, is often the first sign of intestinal infarction. The stool contains occult blood in 75% of patients. Right-sided abdominal pain associated with the passage of maroon or bright red blood in the stool, although characteristic of colon ischemia, also may be seen with AMI, because the blood supply to the right colon and small intestine originates from the SMA. Elderly patients with AMI have been reported to develop mental confusion acutely in as many as 30% of cases.⁵ In patients who survive cardiopulmonary resuscitation and who then develop recurrent bacteremia or sepsis, the suspected cause of sepsis should be NOMI that resulted in a segment of bowel with subacute ischemic injury, acting as a portal for bacterial translocation.⁶ Although episodes of sepsis may be treated successfully with antibiotics, the length of damaged bowel must be removed to prevent recurrent sepsis.

Although abdominal findings early in the course of intestinal ischemia may be minimal or absent, increasing tenderness, rebound tenderness, and muscle guarding reflect progressive loss of intestinal viability. Such abdominal findings strongly indicate the presence of infarcted bowel. The rate of progression from the onset of abdominal pain to intestinal infarction varies not with the specific cause of ischemia but with the severity of the ischemic insult; MVT generally has a more indolent course than do the arterial causes of AMI.

LABORATORY FEATURES AND DIAGNOSIS

On admission to the hospital, approximately 75% of patients with AMI have leukocytosis greater than 15,000 cells/mm³ and about 50% have metabolic acidemia. A normal white blood cell (WBC) count cannot be used to exclude early AMI, just as a high WBC count does not make the diagnosis. Elevated levels of serum phosphate, d-lactate, amylase, and other enzymes have been noted, as have high peritoneal fluid amylase and intestinal alkaline phosphatase activity, but the sensitivity and specificity of these markers of intestinal ischemia have not been established.⁷ More-specific intestinal enzymes including diamine oxidase, hexosaminidase, glutathione S-transferase,⁸ and intestinal fatty acid-binding protein⁹ also lack sufficient sensitivity and specificity to diagnose AMI. Moreover, serum markers, when elevated, usually indicate late-stage disease.

Although they are poorly sensitive (30%) and nonspecific, plain films of the abdomen still are obtained in evaluating patients with suspected AMI. Plain films of the abdomen usually are normal in AMI before infarction. Later on, formless loops of small intestine, ileus, thumbprinting of the small bowel or right colon (Fig. 114-5), or still later, pneumatosis and portal or mesenteric vascular gas may be seen. In one study, the mortality rate of patients with normal plain film studies was 29%, whereas it was 78% in those with abnormal findings.¹⁰ The primary purpose of plain films (or CT scans) is to exclude causes of abdominal pain other than ischemia that might mandate a different therapeutic approach.

Figure 114-5. Plain film of the abdomen showing an ileus and a formless, fixed loop of small intestine (arrows) in a patient with acute mesenteric ischemia from a superior mesenteric artery embolus.

Duplex scanning and Doppler flowmetry can be used to evaluate patients with suspected AMI, but these techniques are limited in their clinical use by the following factors:

CT has largely replaced plain film study of the abdomen for diagnosis and is used to identify arterial and venous thromboses as well as ischemic bowel.^11–14 Findings on CT include colon dilatation, bowel wall thickening, abnormal bowel wall enhancement, lack of enhancement of arterial vasculature with timed intravenous contrast injections, arterial occlusion, venous thrombosis, engorgement of mesenteric veins, intramural gas and mesenteric or portal venous gas (Fig. 114-6), infarction of other organs, ascites, and signs related to the cause of the infarcted bowel such as hernia.¹¹ There are three relatively specific findings of AMI that are better depicted on CT scans compared with plain films: gas in the bowel wall or portal system, acute embolic infarction of other intra-abdominal organs, and thrombi in the mesenteric vessels.¹² Unfortunately, the early signs on CT are nonspecific and the late signs reflect necrotic bowel.

Figure 114-6. Computed tomography (CT) scans of a patient with acute mesenteric ischemia showing gas (arrow) in the portal veins (A) and gas (arrows) in the wall of the intestine as well as the mesentery and its vessels (B). Pneumatosis intestinalis is a late sign of ischemic injury, connotes bowel necrosis, and mandates explorative laparotomy.

In a study of 26 patients with AMI who had a preoperative multislice CT scan followed by exploratory laparotomy, CT scanning identified mesenteric arterial thrombosis in 16 of 17 patients and mesenteric vein thrombosis in 7 of 7 patients, all confirmed at operation. In this study, the sensitivity and specificity of CT scanning for occlusive AMI was 92% and 100%, respectively.¹⁵ The predictive value of CT scanning in the community might not be as high as in this report, because this study used only highly trained radiologists; improved CT scanner technology, however, likely will yield higher detection rates than in the past.

CT angiography has been shown to be promising in the diagnosis of AMI and, in one study, the added CT angiographic findings were believed to alter clinical management in 19% of 62 patients by making the diagnosis of AMI when CT alone did not.¹⁶ Magnetic resonance (MR) angiography and venography are newer imaging techniques used to diagnose AMI; they not only can image the vasculature but might be useful in determining metabolic consequences of inadequate blood flow.^17,18

Laparoscopy may be useful, but it also can be misleading, because early in ischemic injury, blood may be shunted to the serosa, giving a normal appearance to the outside of the bowel even if the mucosa is necrotic. Moreover, laparoscopy is potentially dangerous because SMA blood flow decreases when intraperitoneal pressure exceeds 20 mm Hg.

Selective mesenteric angiography, often with papaverine infusion, currently is the mainstay of diagnosis and initial treatment of both occlusive and nonocclusive forms of AMI, and it should be performed promptly if AMI is suspected or diagnosed on other imaging tests. Sensitivity and specificity of mesenteric angiography for diagnosing AMI in most studies are 90% to 100% and 100%, respectively.¹⁹ Opponents of routine angiography for patients with suspected AMI cite several problems with this approach:

Proponents of angiography accept that the large number of negative angiographic studies is necessary if diagnoses are to be made early enough to improve survival. Prompt laparotomy, however, is indicated in patients with suspected AMI if angiography cannot be performed expeditiously. More controversial is the need for angiography in a patient with suspected AMI and signs of peritonitis. Because such signs usually connote infarcted bowel, the most compelling reason for angiography, namely, diagnosis of AMI while the effects of intestinal ischemia are still reversible, is no longer relevant. Angiography nonetheless still plays an important role in this situation because it can diagnose AMI and its cause and provide a roadmap for revascularization and access for serial postoperative angiographic studies.

TREATMENT

Our approach to the management of AMI is based on several observations. First, if the diagnosis is not made before intestinal infarction, the mortality rate is 70% to 90%. Second, diagnosis of both the occlusive and nonocclusive forms of AMI can be made in most patients by angiography. Third, vasoconstriction, which can persist even after the cause of the ischemia is corrected, is the basis of NOMI and a contributing factor in the other forms of AMI. Finally, vasoconstriction can be relieved by vasodilators infused into the SMA. The cornerstones of our approach, therefore, are the earlier and more liberal use of angiography and the incorporation of intra-arterial papaverine in the treatment of both occlusive AMI and NOMI. Duration of symptoms parallels mortality, and therefore early diagnosis and treatment is paramount to increase the chance for survival.²⁰

AMI should be suspected in patients older than 50 years who have the risk factors previously described and in younger patients—especially those with atrial fibrillation, vasculitis, a coagulation disorder, and those on vasoactive medications—who seek medical attention for sudden, severe abdominal pain that lasts longer than several hours. These patients should be managed according to the algorithm shown in Figure 114-7. Less-absolute indications for inclusion into this protocol consist of unexplained acute abdominal distention, colonoscopic evidence of isolated right-sided colonic ischemia, and acidosis without an identifiable cause.

Figure 114-7. Algorithm for the diagnosis and treatment of intestinal ischemia. CTA, computed tomographic angiogram; DVT, deep venous thrombosis; SMA, superior mesenteric artery. Solid lines show conventional management plan; dotted lines show alternative management plan.

(Modified from Brandt LJ, Boley SJ. AGA technical review on intestinal ischemia: American Gastrointestinal Association. Gastroenterology 2000; 118:954; corrected version in Gastroenterology 2000; 119:281.)

Initial management of patients with suspected AMI includes resuscitation and diagnostic imaging studies. Resuscitation includes relief of acute congestive heart failure and correction of hypotension, hypovolemia, and cardiac arrhythmias. Broad-spectrum antibiotics (e.g., levofloxacin, metronidazole, piperacillin-tazobactam) are given immediately because of the high incidence of positive blood cultures in AMI and because they reduce the extent and severity of ischemic injury in experimental animals.²¹ There are no randomized, controlled trials showing the benefit of antibiotics in AMI, and it is unlikely that such trials will ever be done. After resuscitation, plain films or CT scan of the abdomen are obtained, not to establish the diagnosis of AMI but rather to exclude other causes of abdominal pain. A normal plain film or CT scan does not exclude AMI; ideally, patients are studied before radiologic signs appear because these signs connote irreversibly damaged bowel. If no alternative diagnosis is made on these studies, selective SMA angiography is performed. Based on the angiographic findings and the presence or absence of peritoneal signs, the patient is treated according to the algorithm in Figure 114-7.

Even when the decision to operate has been based on clinical grounds, preoperative angiography should be performed to manage the patient properly at and after laparotomy. Relief of mesenteric vasoconstriction is essential to the treatment of emboli, thromboses, and the nonocclusive low-flow states. Infusion of the phosphodiesterase inhibitor papaverine, through the angiography catheter in the SMA, is used to relieve mesenteric vasoconstriction preoperatively and postoperatively. The papaverine is infused by pump at a constant rate of 30 to 60 mg/hr; papaverine concentrations may vary with the need for fluid restriction.

Although most of the papaverine infused into the mesenteric bed is cleared during one pass through the liver, blood pressure and cardiac rate and rhythm must be monitored constantly. Some patients with liver disease exhibit a drop in blood pressure with this dose of papaverine, but the most common cause of hypotension during the papaverine infusion is dislodgment of the catheter. In patients who have a sudden drop in blood pressure, the papaverine should be replaced with saline or glucose solution and a plain film image of the abdomen should be promptly performed to confirm the catheter’s location. If the catheter has come out of the SMA, it should be replaced and the papaverine should be restarted. The patient’s clinical and angiographic responses to the vasodilator determine the duration of therapy.

Laparotomy is performed in AMI to restore arterial flow obstructed by embolus or thrombosis or to resect irreparably damaged bowel, or both. Embolectomy, thrombectomy, or arterial bypass precedes evaluation of intestinal viability because bowel that initially appears infarcted can show surprising recovery after adequate blood flow is restored. In the operating room, intestinal viability can be assessed clinically, by qualitative or quantitative surface fluorescence or by Doppler ultrasonography.²² Animal models show that administration of intravenous glucagon, intravenous heparin-binding epidermal growth factor (HB-EGF)-like growth factor or intraluminal nitroglycerin after revascularization of an acute arterial occlusion can improve mucosal viability and minimize reperfusion damage.^23,24

In practice, glucagon is sometimes used because of its accessibility and anecdotal beneficial effects despite lack of strong supporting data from human trials. Short segments of bowel that are nonviable or questionably viable after revascularization are resected, and a primary anastomosis is performed. If extensive portions of the bowel are of questionable viability, however, only the clearly necrotic bowel is resected and re-exploration (second look) is planned for within 12 to 24 hours. The interval between the first and second operations is used both to allow better demarcation between viable and nonviable bowel and to attempt to improve intestinal blood flow by using intra-arterial papaverine and by maximizing cardiac output.

The use of anticoagulants in the management of AMI is controversial. Anticoagulation with heparin can cause intestinal or intraperitoneal hemorrhage and, except for MVT, should not be used routinely in the immediate postoperative period; 48 hours after embolectomy or arterial reconstruction, when thrombosis is common, anticoagulation is appropriate.

Specific Types of Acute Mesenteric Ischemia

Superior Mesenteric Artery Embolus

SMAE is responsible for 40% to 50% of AMI episodes. Emboli usually originate from a left atrial or ventricular mural thrombus. Many patients with SMAE have had previous peripheral artery emboli, and approximately 20% have synchronous emboli. SMAEs lodge at points of normal anatomic narrowing, usually immediately distal to the origin of a major branch. Angiography typically reveals a rounded filling defect with nearly complete obstruction to flow. Mesenteric atherosclerosis is usually not as severe as in SMAT. Emboli proximal to the origin of the ileocolic artery are considered major emboli. Minor emboli are those that lodge in the SMA distal to the takeoff of the ileocolic artery or in the distal branches of the SMA (Fig. 114-8).

Figure 114-8. A, Superior mesenteric artery (SMA) angiogram in a 71-year-old man with abdominal pain showing an embolus occluding the SMA at the level of the origin of the right colic artery (arrow). Vasoconstriction is noted distal to the embolus. B, Repeat angiogram done 54 hours after SMA embolectomy and preoperative and postoperative papaverine infusions into the SMA. Vasodilatation is seen, and all vessels are patent except for a distal jejunal branch, which contains a piece of the inciting embolus (arrowhead) that broke off during the course of vasodilator therapy because of endogenous thrombolysis. Papaverine protected the bowel within the distribution of the embolized vessel by enabling vasodilatation and maintenance of adequate blood flow.

Various therapeutic approaches have been proposed for SMAE, depending on the presence or absence of peritoneal signs, whether the embolus is partially or completely occluding, and whether the embolus is above the origin of the ileocolic artery or more distal. Therapy for SMAE has included surgical revascularization, intra-arterial perfusion with vasodilators or thrombolytic agents, and anticoagulation.¹⁹ In the absence of peritoneal signs, minor SMA emboli have been treated successfully with all of these agents without the need for surgery. Exploration is usually performed in patients with major emboli after papaverine infusion is begun. Nonoperative therapy using only papaverine infusion is attempted if there are significant contraindications to surgery, no peritoneal signs, and adequate perfusion of the vascular bed distal to the embolus after a bolus of vasodilator into the SMA.

Exploratory laparotomy is mandatory when peritonitis is present; embolectomy and bowel resection are performed as necessary. If possible, intra-arterial papaverine is begun before surgery and is continued during surgery. If no “second-look” operation is planned, infusion is continued for 12 to 24 hours postoperatively; persistent vasospasm is excluded by angiography before the catheter is removed (see Fig. 114-8). If a second operation is planned, the infusion is continued through the second procedure until angiography shows the vasoconstriction is ceased. Recognition of persistent vasoconstriction has prompted some authorities to recommend routine use of intra-arterial papaverine in all patients with SMAE; the best survival rates are seen in patients treated by this approach.¹⁹

Use of transcatheter thrombolytic therapy (e.g., alteplase or urokinase) can be considered before exploratory laparotomy if the patient does not have signs of peritonitis. Prospective studies and meta-analyses have shown that thrombolysis may be effective in resolving thrombi, improving symptoms, and avoiding surgery in patients with lesions amenable to such therapy.^25,26 Thrombolytic therapy is most likely to be successful when the embolus is partially occluding or is minor and when the study is performed within 12 hours of the onset of symptoms.²⁷ A canine study showed that intra-arterial streptokinase was more effective than intra-arterial papaverine in lysing clots implanted into the SMA, although greater ischemic damage occurred with streptokinase than with papaverine because of papaverine’s action to cause vasodilation and open collateral pathways for blood flow around the obstructing clot. When streptokinase and papaverine were administered simultaneously, neither medication functioned as well as it did alone and intestinal damage was intensified.²⁸ Given the shortage of supporting evidence for thrombolytics in AMI and the high complication rate attending their use, this treatment remains controversial.²⁷

Nonocclusive Mesenteric Ischemia

NOMI is responsible for 20% to 30% of AMI and usually is due to splanchnic vasoconstriction consequent to a preceding cardiovascular event. AMI can appear hours to days after the event, and vasoconstriction, which initially is reversible, can persist even after the precipitating event has been corrected. Precipitating causes for NOMI include acute myocardial infarction, congestive heart failure, arrhythmias, shock, cirrhosis, medications (e.g., digitalis), cardiopulmonary bypass surgery, and chronic kidney disease, especially when patients are on either hemodialysis or peritoneal dialysis. When presenting with abdominal pain, patients on peritoneal dialysis may be thought to have peritonitis, thereby delaying the diagnosis of NOMI and resulting in a poor outcome.²⁹

NOMI is diagnosed by angiography using four criteria: narrowing of the origins of SMA branches, irregularities in the intestinal branches, spasm of the arcades, and impaired filling of intramural vessels. Patients with these signs who are neither in shock nor on vasopressors and who do not have pancreatitis can be considered to have NOMI (Fig. 114-9).

Figure 114-9. Superior mesenteric angiogram in a patient with nonocclusive mesenteric ischemia (NOMI) following a bout of gastrointestinal hemorrhage and shock. A, The pretreatment film shows the diffuse vasoconstriction of NOMI. B, Marked vasodilatation is evident on the repeat study after 48 hours of an intra-arterial papaverine infusion.

(From Brandt LJ, Boley SJ. Ischemic intestinal syndromes. Adv Surg 1981; 15:1.)

SMA infusion of papaverine is begun as soon as the diagnosis is made. Operation is performed if peritoneal signs are present, and the infusion is continued during and after exploration. Necrotic bowel is resected; it is better to leave bowel of questionable viability and perform a second-look operation than to perform massive enterectomy, because compromised but viable bowel often improves with supportive measures. The infusion is continued as for second-look operations following embolectomy.

When papaverine infusion is used as the only treatment for NOMI in patients without signs of peritonitis, it is continued for 24 hours, and repeat angiography is performed 30 minutes after changing the papaverine infusion to normal saline. Papaverine infusion is maintained and angiography repeated daily until there is no roentgenographic evidence of vasoconstriction and the patient’s clinical findings resolve. Infusions, usually discontinued after 24 hours, have been given for as long as 5 days.

Acute Thrombosis of the Superior Mesenteric Artery

Acute SMAT occurs in areas of severe atherosclerotic narrowing, most often at the origin of the SMA. The acute ischemic episode may be superimposed on chronic mesenteric ischemia (CMI), and 20% to 50% of patients have a history of postprandial abdominal pain and weight loss during the weeks to months preceding the acute event. Evidence of coronary, cerebrovascular, or peripheral arterial insufficiency is common.

SMAT is demonstrated on flush aortography, which usually shows occlusion of the SMA 1 to 2 cm from its origin. Some distal filling of the SMA via collaterals is common. Branches proximal and distal to the obstruction can show localized or diffuse vasoconstriction. In patients with abdominal pain, no abdominal tenderness, and complete occlusion of the SMA on aortography, it is important, though difficult, to distinguish between acute thrombosis and long-standing, coincidental chronic occlusion. Prominent collaterals between the SMA and other major splanchnic vessels indicate chronic SMA occlusion. If there is good filling of the SMA, the occlusion is considered chronic and the abdominal pain is considered unrelated to mesenteric vascular disease (see Fig. 114-4). The absence of collateral vessels or the presence of collaterals with inadequate filling of the SMA indicates an acute occlusion and demands prompt intervention. If possible, an angiographic catheter is placed in the proximal SMA, and papaverine infusion is begun before surgery is undertaken.

At surgery, necrotic bowel is resected and remaining bowel is revascularized. Papaverine infusion is continued throughout the operative period, and management is the same as for SMAE. There are only a few reports of use of thrombolytic agents or percutaneous angioplasty for SMAT.

INCIDENCE

In early studies, MVT was believed to be the major cause of AMI, but most of these cases probably represented NOMI. Today, only 5% to 10% of patients with AMI have MVT. The mean age at presentation with MVT is in the mid-60s.³⁶ A Swedish study showed that the highest incidence of MVT was 11.3 per 100,000 person years among those 70 to 79 years old.³⁷

PREDISPOSING CONDITIONS

Previously, a cause of MVT was identified in fewer than half of patients. The discoveries of the primary and secondary hypercoagulable states and the use of estrogens for contraception and hormone replacement have led to identification of the cause in almost 90% of patients.³⁸ Arterial hypertension is the most commonly associated medical comorbidity with this disorder, and neoplasms (e.g., acute lymphocytic leukemia, adenocarcinoma of the pancreas, stomach) and coagulation disorders (e.g., lupus anticoagulant, factor V Leiden, and protein S deficiency) also are commonly seen.^36,39 A list of predisposing conditions for MVT is given in Table 114-3.

Table 114-3 Conditions Associated with Mesenteric Venous Thrombosis

PATHOPHYSIOLOGY

The location of the initial thrombus within the mesenteric venous circulation varies with the cause. MVT secondary to cirrhosis, neoplasm, or operative injury begins at the site of obstruction and extends peripherally, whereas thrombosis of primary hypercoagulable states starts in smaller branches and propagates into the major trunks. Intestinal infarction is rare unless the branches of the peripheral arcades and the vasa recta are involved. When collateral circulation is inadequate and venous drainage from a segment of bowel is compromised, the affected intestine becomes congested, edematous, cyanotic, and thickened with intramural hemorrhage. Serosanguineous peritoneal fluid heralds hemorrhagic infarction. Arterial vasoconstriction can be marked, but pulsations persist up to the bowel wall. Transmural infarction can make it impossible to differentiate venous from arterial occlusion.

CLINICAL FEATURES

MVT can have an acute, subacute (weeks to months), or chronic onset. Except for late complications, chronic MVT is asymptomatic. As many as 60% of patients have a history of peripheral vein thromboses.⁴⁰

Acute MVT manifests with abdominal pain in more than 90% of patients and, as with acute arterial ischemia, the pain initially is out of proportion to the physical findings. The mean duration of pain before admission is five to 14 days, but it is more than one month in as many as 25% of patients.⁴¹ Other symptoms, including nausea and vomiting, occur in more than 50%. Lower gastrointestinal bleeding, bloody diarrhea, or hematemesis occur in 15% and indicate bowel infarction. Fecal occult blood is found in more than half of instances during the course of MVT. Initial physical findings vary at different stages and with different degrees of ischemic injury, but guarding and rebound tenderness develop as bowel infarction evolves. Most patients have a temperature higher than 38°C (100.4°F), and 25% exhibit signs of septic shock.

Subacute MVT describes the condition in patients who have abdominal pain for weeks to months but no intestinal infarction. Subacute MVT can be due either to extension of thrombosis at a rate rapid enough to cause pain but that permits collaterals to develop, thus preventing infarction, or to acute thrombosis of venous drainage sufficient to permit recovery from ischemic injury. The diagnosis usually is made on imaging studies ordered to evaluate the cause of undiagnosed pain. Nonspecific abdominal pain usually is the only symptom of subacute MVT, and physical examination and laboratory tests are normal. Some patients who present with subacute MVT ultimately develop intestinal infarction; this blurs the distinction between the acute and subacute forms of MVT. At autopsy, coexistent new and old thromboses have been found in nearly half of the patients.

Chronic MVT is seen in patients who are asymptomatic at the time of thrombosis but who may develop gastrointestinal bleeding from varices.⁴² Most patients who bleed do so from gastroesophageal varices secondary to portal or splenic vein thrombosis, and they have physical findings of portal hypertension. Laboratory studies may show secondary hypersplenism with pancytopenia or thrombocytopenia.

DIAGNOSIS

Acute Mesenteric Venous Thrombosis

The absence of specific symptoms, signs, or laboratory results and the typical variability in the course of the disease make it difficult to diagnose acute MVT preoperatively. Abdominal plain film signs of MVT are similar to those of other forms of AMI and almost always reflect the presence of infarcted bowel. Barium enemas are of little diagnostic value, because MVT unusually involves the colon. Characteristic findings on small bowel series include marked thickening of the bowel wall due to congestion and edema, with separation of loops and thumbprinting.

Selective mesenteric arteriography can establish a definitive diagnosis before bowel infarction, can differentiate venous thrombosis from arterial forms of ischemia, and can provide access for vasodilator therapy. Angiographic findings of acute MVT include thrombus in the SMV with partial or complete occlusion, failure to visualize the SMV or portal vein, slow or absent filling of the mesenteric veins, arterial spasm, failure of the arterial arcades to empty, reflux of contrast medium into the artery, and prolonged blush in the involved segment.³²

Ultrasonography, CT, and MR imaging all have been used to demonstrate thrombi in the SMV and the portal vein.^43,44 CT can diagnose MVT in more than 90% of patients and is the diagnostic study of choice. Specific findings include thickening and enhancement of the bowel wall, enlargement of the SMV, a central lucency in the lumen of the vein (representing a thrombus), a sharply defined vein wall with a rim of increased density, and dilated collateral vessels in a thickened mesentery (Fig. 114-10). CT also is very accurate in differentiating transmural infarction from non-transmural ischemia.⁴⁵ When MVT is diagnosed on CT scanning, angiography might not be necessary, but in selected symptomatic patients it better delineates thrombosed veins and provides access for intra-arterial vasodilators. Magnetic resonance venography also appears to be highly sensitive for diagnosing MVT and is a diagnostic alternative to CT.⁴⁶ Esophagogastroduodenoscopy and colonoscopy rarely are helpful, because the duodenum and colon are infrequently involved. As in other forms of AMI, laparoscopy may be useful either when other studies are contraindicated or in concert with imaging tests.⁴⁷

Figure 114-10. Superior mesenteric venous thrombosis. A, Abdominal computed tomography (CT) with intravenous contrast demonstrating an enlarged superior mesenteric vein with a central lucency in the lumen, representing the thrombus. The vein wall is sharply defined, with a rim of increased density surrounding the thrombus (arrows). B, Abdominal CT with intravenous contrast agent showing thickening and persistent enhancement of the bowel wall (black arrows) and dilated collateral vessels within a thickened mesentery (white arrows).

(From Boley SJ, Brandt LJ. Ischemic disorders of the intestines. Surg Clin North Am 1992; 72:194.)

The diagnosis of MVT usually has been made at laparotomy, where its hallmarks are serosanguineous peritoneal fluid, dark red to blue-black edematous bowel, thickening of the mesentery, good arterial pulsations in the involved segment, and thrombi in cut mesenteric veins. At this stage, some degree of intestinal infarction invariably has occurred. When persons with suspected AMI exhibit clinical features suggesting MVT, contrast-enhanced CT is performed before SMA angiography, although this recommendation is becoming moot as CT angiography is increasingly used as the initial imaging test.

TREATMENT

PROGNOSIS

Mortality associated with acute MVT is lower than that for other forms of AMI and is approximately 20%. Intestinal infarction, not having a CT scan performed, and treatment on a nonsurgical ward all are associated with increased mortality.³⁷ Recurrence rates of 20% to 25% fall to about 15% if heparin therapy is begun promptly. The natural history of chronic MVT is not known, but from postmortem studies it appears that almost 50% of patients with MVT have no bowel infarction and many have no symptoms.

INCIDENCE

The incidence of CI is underestimated, because many patients suffer only mild or transient damage and do not seek medical attention. Also, CI is commonly misdiagnosed and confused with other disorders, notably inflammatory bowel disease.

In our tertiary care hospital, CI accounts for approximately 1 in 2000 hospital admissions and is seen in approximately 1 in 100 flexible sigmoidoscopies and colonoscopies. A study using medical claims data from a large health care organization calculated a crude incidence rate of 7.2 cases per 100,000 person-years of observation in the general population, in contrast to 42.8 cases per 100,000 person-years for patients with irritable bowel syndrome (IBS). After adjustment for age, sex, and calendar year, the incidence of CI in people with IBS was 3.4 times higher than it was in persons without IBS.⁵⁵

CI has female gender predilection, and more than 90% of patients with CI of non-iatrogenic causes are older than 60 years of age. CI affecting young persons has been documented in case reports or series of a few patients and usually has been due to vasculitis, coagulation disorders, illicit use of cocaine, and a variety of iatrogenic causes, including a wide variety of medications such as estrogens, serotoninergic agonists and antagonists, sumatriptan, and methamphetamine.

PATHOPHYSIOLOGY AND CAUSES

CI can result from alterations in the systemic circulation or from anatomic or functional changes in the mesenteric vasculature, and it is thought to result from local hypoperfusion and reperfusion injury. In most cases, no specific cause for the ischemia is identified, and such episodes are viewed as localized nonocclusive ischemia, likely a result of small-vessel disease. An increasing variety of causes of CI is being defined, including hematologic disorders, thrombophilic states, and medications (see later) (Table 114-5).

Table 114-5 Causes of Colon Ischemia

Abnormalities on angiography rarely correlate with clinical manifestations of disease, but age-related abnormalities in the splanchnic vessels, including narrowing of small vessels, tortuosity of the long colic arteries, and fibromuscular dysplasia (FMD) of the superior rectal artery, can contribute to CI. The colon is particularly susceptible to ischemia, perhaps owing to its relatively low blood flow, its unique decrease in blood flow during periods of functional activity, and its sensitivity to autonomic stimulation. What triggers the episode of CI, however, usually is not known.

PATHOLOGY

Morphologic changes after CI vary with the duration and severity of the injury. The mildest injury is mucosal and submucosal hemorrhage and edema, with or without partial necrosis and ulceration of the mucosa. With more severe injury, chronic ulcerations, crypt abscesses, and pseudopolyps develop, changes that can mimic inflammatory bowel disease (Fig. 114-11).⁷⁵ Pseudomembranes also may be seen. Iron-laden macrophages and submucosal fibrosis are characteristic of ischemic injury. With severe ischemia, the muscularis propria is replaced by fibrous tissue, forming a stricture. The most-severe form of ischemic damage causes transmural infarction.

Figure 114-11. Colonoscopic views of deep ulcerations in a patient with colon ischemia whose illness was misdiagnosed as Crohn’s disease.

CLINICAL FEATURES AND DIAGNOSIS

CI usually manifests with sudden cramping, mild, left lower abdominal pain; an urgent desire to defecate; and passage within 24 hours of bright red or maroon blood or bloody diarrhea. Bleeding is not sufficient to require transfusion. Mild to moderate abdominal tenderness usually is present over the involved segment of bowel. Patients with ischemia isolated to the right side of the colon more often present with lower abdominal pain than they do with rectal bleeding or bloody diarrhea.⁵⁴

A large retrospective study of patients with biopsy-proven CI showed that no region of the colon is spared from involvement. A segmental pattern of involvement is seen most commonly and the sigmoid is affected most often (22.9%), followed by the descending-to-sigmoid colon segment (11.0%), the cecum-to-hepatic flexure segment (8.0%), the descending colon alone (8.0%), and a pancolonic pattern (6.6%).⁷⁶ Although no specific etiology was associated with any specific anatomic distribution, pancolitis and isolated right-sided colonic disease were seen frequently in patients with sepsis.⁷⁶ In older reports, certain causes were believed to affect particular segments: local nonocclusive ischemic injuries, the watershed areas (the splenic flexure and rectosigmoid); ligation of the IMA, the sigmoid. The length of affected bowel can depend on the cause of CI: atheromatous emboli involve short segments, and nonocclusive injuries involve longer portions of colon.

If CI is suspected, a CT scan might support the clinical suspicion and also diagnose potential complications.⁷⁷ If the CT scan shows only nonspecific findings such as a thickened segment of colon, or if the abdominal plain film appears normal, colonoscopy should be performed on the unprepared colon within 48 hours of the onset of symptoms. During colonoscopy and barium enema examination, care should be taken not to overdistend the colon because high intraluminal pressure diminishes intestinal blood flow and can aggravate ischemic damage, particularly in patients with vasculitis.⁷⁸

Colonoscopy is preferable to barium enema because it is more sensitive in diagnosing mucosal abnormalities, and biopsy specimens may be obtained. Hemorrhagic nodules seen at colonoscopy represent bleeding into the submucosa and are equivalent to thumbprints on barium enema studies (Fig. 114-12). Segmental distribution of these findings, with or without ulceration, is highly suggestive of CI, but the diagnosis of CI cannot be made conclusively on the basis of a single examination unless mucosal gangrene is seen (Fig. 114-13). A colonoscopic finding called the colon single-stripe sign has been described in patients with CI, referring to a single line of erythema with erosion or ulceration oriented along the longitudinal axis of the colon; it had a 75% histopathologic yield in making the diagnosis of ischemic injury and signified a milder course than did a circumferential ulcer.⁷⁹ Segmental disease, rectal sparing, and rapid spontaneous evolution usually resulting in resolution of disease are characteristics of CI.

Figure 114-12. Colonoscopic equivalent of a radiologic thumbprint, caused by subepithelial hemorrhage and edema, in a patient with colon ischemia.

Figure 114-13. Colonoscopic view of mucosal gangrene in a patient with colon ischemia. The necrotic epithelium appears black against the relatively healthier tissue.

The initial diagnostic study should be performed within 48 hours, because thumbprinting disappears within days as the submucosal hemorrhages are resorbed or the overlying mucosa sloughs. Studies performed one week after the initial study should reflect evolution of the injury—either normalization of the colon or replacement of the thumbprints with a segmental ulcerative colitis-type pattern (Fig. 114-14). Universal colonic involvement, however, favors true ulcerative colitis, whereas fistula formation suggests Crohn’s disease. Occasionally, an abundant inflammatory response can produce heaping up of mucosa and submucosa that resembles a stricture or neoplasm (Fig. 114-15).

Figure 114-14. Films from serial barium enema examinations in a patient with reversible ischemic damage to the transverse colon and splenic flexure. A, Initial study shows dramatic thumbprints (arrows) throughout the area of involvement. B, Eleven days later, the thumbprints have resolved, and the involved colon has the appearance of segmental colitis. C, Five months after the onset, the colon has returned to normal. The patient was asymptomatic by three weeks after the onset of her illness.

(From Boley SJ, Schwartz SS. Colonic ischemia: Reversible ischemic lesions. In Boley SJ, Schwartz SS, Williams LF, editors. Vascular disorders of the intestines. New York: Appleton-Century-Crofts; 1971. p 589.)

Figure 114-15. Colonoscopic view of colon ischemia resembling neoplasia in a patient with metastatic cancer treated with interleukin-2 and interferon-α. The inflamed, edematous mass was thought to be due to cecal neoplasia. The lesion resolved spontaneously after just five days.

(From Sparano JA, Dutcher JP, Kaleya R, et al. Colonic ischemia complicating immunotherapy with interleukin-2 and interferon-α. Cancer 1991; 68:1538.)

At the time of symptom onset, colon blood flow typically has returned to normal; therefore, mesenteric angiography usually is not indicated. An exception to this rule is when the clinical presentation does not allow a clear distinction to be made between CI and AMI or perhaps when only the ascending colon is involved. Administration of air during flexible sigmoidoscopy or a limited colonoscopy can subsequently and immediately be used to reveal thumbprinting not otherwise visible on abdominal plain films; thumbprints stand out as relatively radiodense nodules against the radiolucency of the administered air. Nodules in the left colon or throughout the colon imply CI, whereas nodules isolated to the ascending colon suggest the possibility of otherwise silent SMA disease and the need to evaluate the mesenteric vasculature.

CLINICAL COURSE AND TREATMENT (Fig 114-16)

When CI is diagnosed and physical examination does not suggest gangrene or perforation, the patient is treated expectantly. Parenteral fluids are administered and the bowel is placed at rest. Broad-spectrum antibiotics are given to cover the fecal flora because in experimental models, antibiotics reduce the extent and severity of bowel damage. No randomized, controlled, blinded trials have been done to prove the validity of this recommendation. An electrocardiogram, Holter monitoring, and transthoracic echocardiogram should be obtained to exclude or confirm a cardiac source of embolism. Patients with segmental, nongangrenous CI undergoing such evaluation are 2.5 times more likely to have their cardiac risk factor identified compared with other patients with CI.⁸⁰ Cardiac failure and arrhythmias are treated, and medications that can cause mesenteric vasoconstriction are withdrawn. If the colon appears distended, it is decompressed with a rectal tube. Serial imaging tests of the colon and continued monitoring of the hemoglobin level, WBC count, and electrolyte levels are indicated until the patient’s condition stabilizes.

Figure 114-16. Algorithm for the management of colon ischemia. Solid lines indicate conventional management plan; dashed line indicates alternative management plan. BE, barium enema; IBD, inflammatory bowel disease; IV, intravenous; NPO, nothing by mouth; PLC, protein-losing colopathy.

(From Brandt LJ, Boley SJ. AGA technical review on intestinal ischemia: American Gastrointestinal Association. Gastroenterology 2000; 118:954.)

Increasing abdominal tenderness, guarding, rebound tenderness, rising temperature, and paralytic ileus indicate colonic infarction and demand immediate laparotomy and colon resection if appropriate. At operation, mucosal injury may be extensive despite normal-looking serosa, and the extent of resection should be guided by the distribution of disease as seen on preoperative studies rather than the appearance of the serosal surface of the colon at the time of operation.

In more than half of patients with CI, the disease is reversible. Generally, the symptoms of CI resolve within 48 to 72 hours and the colon heals in one to two weeks. With severe injury, it can take one to six months for the colon to heal; however, during this time the patient is usually asymptomatic. A retrospective study of 350 patients with biopsy-proven CI showed that those with isolated right-sided colon ischemia had a worse outcome than those with CI isolated to other segments, including a five-fold increase in the need for surgery and a two-fold increase in mortality.⁵⁴ Another retrospective study showed that patients’ ages, leukocyte counts, lactate dehydrogenase levels, blood lactate levels, and absence of vascular flow to the colonic wall on abdominal Doppler ultrasonography were independent predictors of complicated CI; only absence of arterial flow was a significant predictor of complicated disease when confounding for other factors.⁸¹ Symptoms that persist for more than two weeks also are associated with a higher incidence of acute complications and irreversible disease: gangrene and perforation, segmental ulcerating colitis, or stricture.

SPECIAL CLINICAL PROBLEMS

Colon Ischemia in Patients with Carcinoma of the Colon and Other Potentially Obstructive Lesions

Less than 5% of patients with CI have a distal and potentially obstructing lesion or disorder, including carcinoma of the colon, diverticulitis, volvulus, fecal impaction, postoperative stricture, prior ischemic stenosis, or radiation stricture. Typically, the associated lesion is distal, and there is a segment of normal colon between the distal lesion and the proximal colitis (Fig. 114-17). The mechanism of this association may involve increased intracolonic pressure proximal to the lesion with resultant decreased colon blood flow.

Figure 114-17. Film from a barium enema demonstrating a narrowed segment of colon ischemia (upper arrow) proximal to a carcinoma in the distal sigmoid (lower arrow). The area of colon between the carcinoma and the ischemic segment is normal.

(From Boley SJ, Brandt LJ, Veith FJ. Ischemic disorders of the intestines. Curr Probl Surg 1978; 15:1.)

CLINICAL FEATURES

The cardinal clinical feature of CMI is abdominal cramping discomfort that usually occurs within 30 minutes after eating, gradually increases in severity, and then slowly resolves over one to three hours. Although minimal at first, abdominal pain progressively increases in severity over weeks to months. The association of pain with meals leads to fear of eating, with resultant weight loss. Nausea, bloating, episodic diarrhea, and malabsorption or constipation can occur, but it is the weight loss and relation of the abdominal pain to the meals that characterize this syndrome. Early in the course of disease, if patients do not eat, they remain pain free; pain occurs only after eating or during a meal. Later, pain can become continuous, and this portends intestinal infarction.

Uncommon presentations of CMI include antral ulcerations that are unassociated with Helicobacter pylori and that do not heal on therapy with proton pump inhibitors; gastroparesis that resolves after revascularization; and acalculous cholecystitis. Approximately one third to one half of patients have evidence of cardiac, cerebral, or peripheral vascular disease. Physical findings are usually limited, but patients with advanced disease can appear cachectic. The abdomen typically remains soft and nontender even during painful episodes, although distention may be appreciated. An abdominal bruit is common but nonspecific.

DIAGNOSIS

Diagnosis of CMI is difficult because of the vague nature of the complaints and the lack of a specific diagnostic test. Abdominal plain films and CT scans are usually normal, although vascular calcification may be present. Endoscopic inspection of the gastrointestinal tract usually reveals it to be normal, and random biopsies of the upper tract might show only nonspecific abnormalities; a diagnostic clue may be antral ulcerations that are unassociated with H. pylori and that do not heal on acid-suppression therapy. Barium studies are normal or show nonspecific evidence of either malabsorption or a motility disturbance. Rarely, radionuclear emptying tests might show delayed gastric emptying.

Ultrasonography, MR angiography, and even traditional mesenteric angiography all merely reveal morphologic abnormalities and anatomic limitations of splanchnic blood flow; they do not establish the presence or absence of intestinal ischemia. Duplex ultrasonography can be used to identify splanchnic artery stenoses but not to establish the diagnosis of CMI.⁹⁰ Elevated peak systolic velocity in the SMA and CA of 275 and 200 cm/sec, respectively, is a reliable sign of at least 70% stenosis of these vessels.⁹¹ Duplex ultrasonography and phase-contrast cine MR imaging of the SMA and CA have been used to measure the effect of eating on mesenteric blood flow, all based on the principle that eating normally increases blood flow to the small intestine, whereas in CMI, this fails to occur; however, postprandial studies are no better than fasting examinations, especially at lesser degrees of vascular stenosis.⁹¹

Gastric tonometry exercise testing (GET) uses a nasogastric tube and peripheral arterial catheter to obtain gastric juice and arterial blood from a fasting patient who has been given acid-suppression medication. Determination is made of the gastric-arterial Pco₂ gradient before, during, and after exercise. An increase in the gradient after exercise is an indicator of gastrointestinal ischemia. In a study of the diagnostic accuracy for chronic gastrointestinal ischemia, GET and duplex sonography, alone and in combination, were compared with the gold standard, angiography. Combined GET and duplex sonography would not have missed any patients with symptomatic gastrointestinal ischemia; therefore, they are currently believed to constitute the best diagnostic workup strategy.⁹² More experience with these provocative tests is needed, however, before firm conclusions can be made about their diagnostic usefulness.

In the absence of any specific, reliable diagnostic test, the diagnosis of CMI is based on clinical symptoms, in combination with radiologic demonstration of an occlusive process of the splanchnic vessels, and, to a great measure, the exclusion of other gastrointestinal disorders. Angiography should show occlusion of two or more splanchnic arteries to allow the diagnosis of CMI; however, such occlusions, even of all three vessels, do not by themselves make the diagnosis of CMI, because they may be present with no corresponding clinical symptoms. In most patients with CMI, at least two of the three splanchnic vessels either are completely obstructed or severely stenotic. In a review of series of patients with CMI,⁸⁸ 91% had occlusion of at least two vessels and 55% had involvement of all three; 7% and 2% had isolated occlusion of the SMA and CA, respectively.

TREATMENT

CMI is not considered to require urgent therapy, although acute complete occlusion of the gastrointestinal blood supply can occur if thrombosis is superimposed on already narrowed arteries. A patient with the typical pain of CMI and unexplained weight loss whose diagnostic evaluation has excluded other gastrointestinal disease and whose angiogram shows occlusive involvement of at least two of the three major arteries should undergo revascularization (Fig. 114-18).

Figure 114-18. Algorithm for the management of chronic mesenteric ischemia. Solid lines indicate conventional management plan; dashed lines indicate alternative management plan. CTA, computed tomographic angiography; MRA, magnetic resonance angiography.

(Modified from Brandt LJ, Boley SJ. AGA technical review on intestinal ischemia: American Gastrointestinal Association. Gastroenterology 2000; 118:954.)

Surgical revascularization has been the traditional method of therapy for patients with CMI. Since the early 1980s, percutaneous transluminal mesenteric angioplasty (PTMA) alone or with stent insertion has been used as alternative therapy. The results of surgical revascularization for CMI vary in different reports, depending on the nature of the operations used, the number of vessels revascularized, and whether concurrent operations such as aortic reconstruction are performed.

The true efficacy of surgical revascularization and PTMA is difficult to determine because of the varied criteria used by different investigators to define a successful outcome. Thus, some authors use graft or vessel patency rates, whereas others define success by relief of symptoms, recurrence rates, or long-term survival. A tabulation of 17 series of surgical revascularization for CMI totaling 614 patients yielded perioperative mortality rates that ranged from 0%^93–98 to 16%,⁹⁹ success rates of 59%¹⁰⁰ to 100%,^94–98 and recurrence rates of 0%^{85,93,94,99,101,102} to 26.5%.¹⁰³ Most recent series have reported mortality rates less than 10%, success rates of more than 90%, and recurrence rates generally less than 10%.¹⁹ Several long-term studies have shown that patients surviving surgical revascularization have cumulative 5-year survival rates of approximately 80% to 90%.¹⁹

The rates of success for PTMA are similar to those for surgical revascularization. The experience with PTMA is more limited but has been achieved in patients often considered too high risk for a surgical procedure. In 10 representative series of PTMA for CMI, totaling 128 patients, clinical success rates (i.e., relief of symptoms) have varied from 63%¹⁰⁴ to 100%,¹⁰⁵ with little mortality.¹⁹ Recurrence of symptoms, however, has been much higher than after surgical revascularization, varying from 10% to 67% in the larger series.¹⁹ Intraluminal stenting is an adjunctive treatment to PTMA and attempts to decrease the incidence of recurrent stenoses. Percutaneous transluminal mesenteric angioplasty with stenting (PTMAS) results in the same short-term patency rates for both stenotic and occluded vessels.¹⁰⁶ Long-term studies of PTMAS patency rates indicate that approximately 70% are patent at seven years and 56% of patients are free from recurrent symptoms. When compared with open surgical bypass, PTMAS shows a decreased primary patency, decreased primary assisted patency, and earlier required reinterventions.¹⁰⁷

Patients with CMI who are otherwise relatively healthy probably should be treated by surgical revascularization; patients at poorer risk should have an initial attempt at PTMA or PTMAS to relieve symptoms.

ALLERGIC GRANULOMATOUS ANGIITIS (CHURG-STRAUSS SYNDROME)

Allergic granulomatous angiitis is a disorder that is typified by asthma, glomerulonephritis, eosinophilia, and granulomatous inflammation associated with antineutrophil cytoplasmic autoantibodies.¹⁰⁹ Necrotizing vasculitis affects small and medium-sized vessels and involves the gastrointestinal tract in almost half the patients. As in other vasculitides, abdominal pain and bleeding secondary to ischemia are the usual manifestations. Glucocorticoid therapy usually is effective.

BEHÇET’S DISEASE

Behçet’s disease (see Chapter 35) is characterized by oral and genital ulcers, recurrent iritis or chorioretinitis, and skin lesions. It is most often seen in Eastern Mediterranean men and is strongly associated with the B51 allele. Small-vessel vasculitis accounts for much of the damage, but large-vessel involvement of arteries and veins is not uncommon. Gastrointestinal disease, present in 50% of patients, typically involves the ileocecal area, although involvement of the esophagus and small intestine has been reported.¹¹⁰ Attacks are recurrent and usually self-limited except for the uveitis which may be chronic. The most common gastrointestinal symptoms are abdominal pain, diarrhea, and bleeding; deep ulcers are responsible for the most common intestinal complications: severe bleeding and perforation. Mortality is low in Behçet’s disease; however, intestinal perforation is one of the common causes of death. Therapy with glucocorticoids, immunosuppressive agents, and colchicine has been tried, with varying success.

BUERGER’S DISEASE

Also called thromboangiitis obliterans, Buerger’s disease involves medium-sized and small peripheral arteries and veins, especially the infrapopliteal vessels; foot claudication and rubor are the most common symptoms. It is largely a disease of men, especially those who have smoked cigarettes from an early age, and typically has its onset before the age of 50 years; there is a distinct absence of other atherosclerotic risk factors. Intestinal involvement is unusual, but most common is involvement of the vessels supplying the small intestine.¹¹¹ In the acute lesion, inflammation spreads outward from the thrombus-endothelium interface through the vessel wall. Later, microabscesses, necrotizing granulomas, and multinucleated giant cells occur in the thrombus, after which the thrombus organizes and becomes occlusive. Intestinal involvement usually requires resection.

COGAN’S SYNDROME

Cogan’s syndrome is a rare disorder of young people characterized by vasculitis of the conjunctiva, cornea, and cochlea.¹¹² Although this vasculitis usually is localized, it is considered to be a hypersensitivity reaction to an unknown viral agent, and the disease can become disseminated. Three percent to 10% of patients develop gastrointestinal symptoms, with diarrhea and bloody stools. High-dose glucocorticoids, and occasionally cytotoxic agents, are required. Vascular surgery may be needed after inflammation is controlled.

FIBROMUSCULAR DYSPLASIA

FMD is a rare angiopathy that is neither related to atherosclerosis nor to inflammation.¹¹³ Its cause is unknown, although genetic factors might play a role and there is an association with cigarette smoking and hypertension. There are several types of FMD depending on which arterial layer is involved: intima, media, or adventitia. The renal arteries are most commonly involved, followed by the carotid and vertebral arteries and then other vasculature including the mesenteric arteries. Splanchnic involvement can manifest with symptoms of AMI or CMI.¹¹⁴ Diagnosis is based on the same techniques used to image other vascular disorders; the classic string-of-beads appearance is typical of only the medial type of FMD, whereas aneurysms and dissection are known complications of all types. Therapy consists of percutaneous transluminal angioplasty, surgical revascularization, and resection of necrotic bowel as indicated.

HENOCH-SCHÖNLEIN PURPURA

Henoch-Schönlein purpura (see Chapter 35) typically affects children aged 4 to 7 years. It is characterized by IgA immune complexes deposited within the small vessels of the skin, gastrointestinal tract, joints, and kidneys and is often preceded by an upper respiratory infection. The classic clinical triad consists of palpable purpura (usually below the waist), arthritis (knees and ankles), and abdominal pain; the gastrointestinal tract is involved in up to 75% of patients.¹¹⁵ Abdominal pain and gastrointestinal bleeding are the most common gastrointestinal symptoms and are caused by mucosal and submucosal hemorrhage; a submucosal hematoma may be the lead point of an intussusception. Gastrointestinal involvement may be documented by endoscopy¹¹⁶ or by CT study.¹¹⁷ The disease is usually self-limited, but the outlook may be less favorable in adults, in large measure because of the development of renal failure.

HYPERSENSITIVITY VASCULITIS

Hypersensitivity vasculitis uncommonly involves the splanchnic vasculature, and, in contrast with necrotizing vasculitis, which involves arteries, affects mainly the postcapillary venules. A large variety of causes are known to trigger this disorder, including infections (Streptococcus, Staphylococcus, hepatitis B virus, influenza virus, cytomegalovirus, mycobacteria, and rickettsiae), drugs, and chemicals.

KAWASAKI’S DISEASE

Kawasaki’s disease, also called infantile febrile mucocutaneous lymph node syndrome, is a necrotizing vasculitis of medium-sized arteries.¹¹⁸ It manifests as fever, rash on the palms and soles, desquamation, conjunctival congestion, strawberry tongue, and cervical lymphadenopathy in infants and children. Many patients have nausea, vomiting, abdominal pain, and diarrhea, and they can suffer ileus, small bowel obstruction, bleeding, and perforation. Death may be due to coronary artery aneurysms and myocardial infarction. Treatment is aspirin for the acute phase and large intravenous doses of gamma globulin for the prevention of coronary artery aneurysms.

KÖHLMEIER-DEGOS DISEASE (MALIGNANT ATROPHIC PAPULOSIS)

Köhlmeier-Degos disease is a rare form of progressive occlusive vascular disease of young men that affects the small and medium-sized arteries, mainly those of the skin and intestine.¹¹⁹ Typically, skin lesions of porcelain-white punctate scars with erythematous borders are found on the trunk and upper extremities. The rash is followed, within months to years, by the development of abdominal pain and spontaneous intestinal perforation. Thrombosis of small and medium-sized vessels is found, without inflammatory cell infiltration. There is no known therapy for this disease, and it is generally fatal.

POLYARTERITIS NODOSA

Polyarteritis nodosa (see Chapter 35) is a necrotizing vasculitis of medium-sized and small arteries characterized by aneurysms at branch points. Abdominal symptoms are reported in up to half of patients with the disorder, the most common of which is abdominal pain, usually from ischemia.¹²⁰ Involvement of the small intestine is most common, followed by lesions of colon, liver, and pancreas. Diagnosis is suggested by typical angiographic findings of aneurysms in the mesenteric, renal, and hepatic vasculature. Treatment with glucocorticoids and cyclophosphamide or azathioprine has improved survival greatly.

Vasculitis resembling polyarteritis also is associated with hepatitis B and C virus infections.^121,122 Fifty percent of patients with classic polyarteritis are hepatitis B surface antigen positive, but unlike in classic polyarteritis, only small arteries are involved. Patients develop a polyarteritis picture following the viral infection, presumably from deposition of antigen-associated immune complexes on the vessel wall.

RHEUMATOID VASCULITIS

Rheumatoid vasculitis affects the gastrointestinal tract in approximately 10% of patients, usually those who have subcutaneous nodules and who are seropositive for rheumatoid factor.¹²³ As with all vasculitides, ischemia manifests with abdominal pain, bleeding, perforation, and gangrene. Other diseases have been noted in association with rheumatoid arthritis, including atrophic gastritis, gastric antral vascular ectasia, inflammatory bowel disease, collagenous colitis, and amyloidosis.

SYSTEMIC LUPUS ERYTHEMATOSUS

Systemic lupus erythematosus (see Chapter 35) affects the gastrointestinal system in about half of cases and can involve any of the hollow and solid gastrointestinal organs.¹⁰⁸ The most common symptoms are nausea, vomiting, and abdominal pain, but diarrhea, malabsorption, pseudo-obstruction, peritonitis, pancreatitis, protein-losing enteropathy, and ascites are also well-known occurrences. The systemic nature of the disorder makes differential diagnosis complicated, but vasculitis-induced ischemia underlies many of the presentations. The vasculitis typically involves small vessels and causes FSI and gastrointestinal bleeding, both of which are associated with high mortality rates if not diagnosed promptly.

TAKAYASU’S DISEASE

Takayasu’s disease (pulseless disease) is an idiopathic chronic inflammatory disorder that most often affects the aorta and its branches in young women of Asian heritage; it is unusual that the splanchnic vessels are involved.¹²⁴ Fibrotic occlusion of the involved vessels is the end result of the inflammatory process. Takayasu’s disease rarely has been associated with Crohn’s disease and ulcerative colitis, and in the serum of some of these patients, antibodies to colonic mucosa and aorta have been detected. Treatment is large doses of glucocorticoids before reconstructive surgery. The five-year survival rate is higher than 90%.