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Visceral Arteries
The arterial anatomy of the gastrointestinal tract is the most variable of all vascular beds. In addition, there is great diversity in the types of diseases that involve the gastrointestinal arteries and organs. Many visceral disorders, vascular and otherwise, can be treated effectively with endovascular techniques. As a result, visceral arterial diagnosis and intervention continues to be an important aspect of interventional radiologic practice.
Normal Anatomy
Celiac Artery
The celiac artery arises from the anterior surface of the abdominal aorta at the level of the T12-L1 disk space ( Fig. 11-1 ). In most individuals, the inferior phrenic arteries arise from the aorta in close proximity to the upper rim of the celiac artery orifice, but sometimes from the very proximal celiac artery. The celiac artery (also known as the celiac trunk) courses inferiorly under the posterior fibers of the diaphragmatic crura for a distance of 1.5-3 cm. There is frequently an indentation upon the superior aspect of the celiac artery caused by the fibers of the diaphragm ( Fig. 11-2 ), which is made worse and can even occlude the lumen with expiration. Branches of the celiac artery supply the stomach, pancreas, liver, and spleen ( Fig. 11-3 ).
The first branch of the celiac artery is usually the left gastric artery, arising superiorly distal to the diaphragmatic crura. Distal to the left gastric artery, the celiac artery bifurcates into the common hepatic and splenic arteries. A large branch to the pancreas, the dorsal pancreatic artery, may arise from the celiac, proximal hepatic, or splenic arteries. Conventional celiac artery anatomy is present in only 70% of individuals. A wide range of variants can occur ( Table 11-1 ). An awareness of these variations and knowing where to look for celiac branches that may have anomalous origins are essential for visceral vascular imaging. Specific examples are provided in the following sections. As a rule, any of the celiac branches can arise independently from the aorta, or (with the exception of the left gastric artery) from the superior mesenteric artery (SMA). Rarely, the entire celiac artery can be replaced to the SMA. These variants are explained by the common embryology of the contents of the peritoneal cavity. For the same reason, celiac branches cannot arise anomalously from the renal arteries, because these organs are retroperitoneal in origin.
Table 11-1
Celiac Artery Anatomy
| Incidence | |
|---|---|
| Left gastric, splenic, common hepatic arteries from celiac trunk | 70% |
| Above plus dorsal pancreatic artery from celiac trunk | 10% |
| Splenic, common hepatic arteries from celiac trunk; left gastric from aorta | 2% |
| Splenic, left gastric arteries only from celiac trunk | 3% |
| Common hepatic, left gastric arteries only from celiac trunk | <1% |
| Celiacomesenteric trunk (shared origin celiac and superior mesenteric arteries) | <1% |
| All branches individually from aorta | <1% |
| Splenic artery from aorta | <1% |
| Splenic artery from superior mesenteric artery | <1% |
Liver (Arterial Supply)
The liver parenchymal anatomy is most often described using the Couinaud segments, based upon hepatic and portal venous anatomy (see Fig. 14-1 ). This chapter focuses on the arterial anatomy.
One third of the blood flow to the liver is arterial, but this supplies two thirds of the organ’s oxygen. Conversely, the portal vein supplies two thirds of the blood volume, but only one third of the oxygen. The common hepatic artery arises from the celiac artery in more than 95% of individuals. The terminal branches of this artery are the gastroduodenal and proper hepatic arteries (see Fig. 11-3 ). In a little over half of patients, the proper hepatic artery gives rise to the entire arterial supply of the liver ( Table 11-2 ). The proper hepatic artery continues for a short distance, and then divides into the left and right hepatic arteries. A separate branch to segments 4a and 4b, the middle hepatic artery, is often present. The left hepatic artery has a characteristic forked appearance that allows ready identification. The hepatic arteries are located anterior to the portal vein within the liver parenchyma.
Table 11-2
Hepatic Arterial Anatomy
| Incidence | |
|---|---|
| All branches from common hepatic artery | 55% |
| Right hepatic artery from superior mesenteric artery (SMA) | 12% |
| Accessory right hepatic artery from SMA | 6% |
| Left hepatic from left gastric artery | 11% |
| Accessory left hepatic from left gastric artery | 11% |
| Right hepatic from SMA and left hepatic from left gastric artery | 2% |
| Common hepatic artery from SMA | 2% |
| Common hepatic artery from aorta | 2% |
| Right hepatic artery from celiac | <1% |
The most common variants of hepatic arterial supply are replacement of part or all of the right hepatic artery from the SMA, or the left hepatic artery replaced to the left gastric artery ( Fig. 11-4 ). These variants can occur in isolation or together. In general, 45% of patients have some variation in their hepatic arterial supply.
The cystic artery (to the gallbladder) is usually a branch of the right hepatic artery, although it may arise from the common hepatic, left hepatic, or even the superior mesenteric arteries (see Fig. 11-3 ).
Spleen
The spleen derives its blood supply from the celiac artery primarily via the splenic artery (see Figs. 2-21 and 11-3 ). This vessel courses posterior to the pancreas, and anterior and superior to the splenic vein. The splenic artery is much longer than the hepatic artery, and frequently several millimeters larger in diameter. The splenic artery gives rise to many small branches to the pancreas and stomach. The splenic artery divides into multiple branches, usually in the hilum of the spleen but sometimes in a more proximal location.
Stomach
The stomach is supplied by numerous arteries, all of which communicate with each other (see Fig. 11-3 ). The left gastric artery is usually the first branch of the celiac artery but can also arise directly from the aorta or rarely from the left hepatic artery. The left gastric artery supplies the gastroesophageal junction, fundus of the stomach, and a portion of the lesser curve. The lateral fundus is also supplied by short and posterior gastric arteries arising from the splenic artery and splenic hilum. These arteries anastomose with the left gastric artery.
The body of the stomach is supplied by the gastroepiploic artery, which is located along the greater curvature of the stomach (see Fig. 11-3 ). The gastroepiploic artery has origins from the gastroduodenal artery (where it is called the right gastroepiploic artery) and the distal splenic artery (where it is called the left gastroepiploic artery). The lesser curvature of the body of the stomach is supplied by branches from the right gastric artery and branches of the left gastric artery ( Fig. 11-5 ). The right gastric artery usually arises from the left or common hepatic arteries, and is a much smaller vessel than the left gastric artery.
The antrum and pylorus are supplied by the right gastroepiploic and right gastric arteries. In addition, the pancreaticoduodenal arteries (branches of the gastroduodenal artery) provide blood supply to this part of the stomach.
Pancreas
The pancreatic blood supply is derived from both the celiac artery and the SMA. The head of the pancreas is supplied by the pancreaticoduodenal arteries (see Figs. 11-3 and 11-6 ). These vessels are paired arteries anterior and posterior to the pancreatic head. They are further divided into superior and inferior vessels. The superior pancreaticoduodenal arteries arise from the gastroduodenal artery, while the inferior pancreaticoduodenal arteries arise from a common trunk off the proximal SMA.
The body of the pancreas is supplied by the dorsal pancreatic artery, usually a proximal branch of the splenic artery or the celiac artery, which contributes to the transverse pancreatic artery running the length of the gland (see Figs. 11-3 and 11-6 ). Less commonly, the dorsal pancreatic artery will arise from the common hepatic artery, the SMA, or the aorta. This is a small but important artery, in that it can contribute to the blood supply of the transverse colon via an accessory or a replaced middle colic artery in 1%-2% of patients ( Fig. 11-7 ). The pancreaticoduodenal arteries also supply the body of the pancreas through the transverse pancreatic artery.
There are numerous small arteries that arise directly from the splenic artery to supply the body and tail of the pancreas. These are termed, aptly, small pancreatic arteries. The largest and most distal of these vessels is the pancreatica magna artery. All of these arteries communicate with the transverse pancreatic artery. The left gastroepiploic artery may provide small branches to the tail of the pancreas.
Superior Mesenteric Artery
There are usually four sources of arterial supply to the small bowel and colon: the gastroduodenal branches from the celiac artery, the SMA, the inferior mesenteric artery (IMA), and the anterior divisions of the internal iliac arteries. The SMA supplies the duodenum, small bowel, and the colon as far as the splenic flexure ( Fig. 11-8 ). The IMA supplies the left colon, sigmoid colon, and proximal rectum ( Fig. 11-9 ). The internal iliac arteries provide supply to the rectum and anus (see Fig. 10-2 ). The vasculature of the bowel is, in essence, one long multitiered arcade. The most peripheral continuous vessel in this arcade runs along the mesenteric border of the bowel. In the colon, this vessel is usually well developed and termed the marginal artery of Drummond. The equivalent vessel in the small bowel is less prominent and unnamed. The classic areas of overlap (watershed areas) of the bowel vascular supply are the splenic flexure of the colon (Griffith point) and the superior rectum.
The SMA arises from the anterior abdominal aorta 1-2 cm distal to the celiac artery (see Figs. 11-1 and 11-2 ). The SMA is typically 6-8 mm in diameter at its origin. The SMA passes behind the body of the pancreas and over the left renal vein, and runs through the mesentery slightly to the right and posterior to the superior mesenteric vein (SMV). The first major branch of the SMA is either the inferior pancreaticoduodenal artery trunk or the middle colic artery. These two vessels can also arise conjointly. The middle of the SMA supplies the small bowel from the third portion of the duodenum to the terminal ileum through multiple branches that usually arise from the left border of the vessel. These are termed jejunal or ileal branches based upon the portion of small bowel that they supply. The right side of the artery gives rise to the right colic artery, which supplies the ascending colon. The SMA terminates in the ileocolic artery, which supplies the terminal ileum and the cecum. A small appendiceal artery may arise from the ileocolic artery or directly from the distal SMA. The middle and right colic arteries bifurcate at the mesenteric border of the colon; the right into ascending and descending branches, and the middle into right and left branches. Of particular importance is the left branch of the middle colic, in that this artery anastomoses with the left colonic branches of the IMA.
In fewer than 1% of patients, the celiac artery and SMA share a common origin from the aorta. This is termed a celiacomesenteric trunk . The SMA frequently gives rise to an accessory or replaced right hepatic artery (20%), or less commonly a replaced proper or common hepatic artery (2%) (see Fig. 11-4 ). In fewer than 1% of patients, the splenic, transverse pancreatic, or dorsal pancreatic arteries may arise from the SMA. A persistent direct fetal communication between the celiac artery and the SMA, in conjunction with or distinct from the dorsal pancreatic artery, occurs in fewer than 1% of patients and is termed the arc of Buhler (see Figs. 11-6 and 11-8 ). A separate origin of some of the jejunal, ileal, or colic branches from the anterior surface of the aorta between the SMA and IMA, known as a middle mesenteric artery , is extremely rare. If you find a case, please send it to me!
Inferior Mesenteric Artery
The IMA arises from the left side of the anterior distal abdominal aorta at the level of the L3 vertebral body, approximately 2-3 cm above the aortic bifurcation (see Fig. 11-1 ). This artery is much smaller than the SMA in diameter, usually no more than 3 mm. The artery has a sharply caudal course through the sigmoid mesentery (see Fig. 11-9 ). The first branch of the IMA is the left colic artery, from which a large branch ascends through the mesentery to meet the left branch of the middle colic artery at the splenic flexure. The blood supply of the sigmoid colon is provided by the IMA. The terminal branch of the IMA is the superior hemorrhoidal artery to the superior rectum. This is located in the center of the pelvis. On conventional angiography, the distal superior hemorrhoidal artery has a characteristic forked appearance, which distinguishes it from the straight median sacral artery. On a lateral view, the hemorrhoidal artery is in the middle of the pelvis, whereas the median sacral artery lies close to the anterior surface of the sacrum. The remainder of the rectum is supplied by the middle and inferior rectal arteries, terminal branches of the anterior division of the internal iliac arteries.
Key Collateral Pathways
Celiac Artery
The pancreaticoduodenal arteries from the SMA are the dominant collateral supply to the celiac artery (see Fig. 11-6 ). Primitive transpancreatic communications from the SMA through the dorsal pancreatic artery, such as the arc of Buhler, can exist in some individuals. These same circuits can provide collateral supply to the SMA from the celiac artery.
Spleen
The spleen receives collateral blood supply from the left gastric artery via the short gastric arteries, the right gastroepiploic to the left gastroepiploic arteries, arteries from the tail of the pancreas, and omental collaterals (arc of Barkow). Proximal splenic artery occlusion is usually well tolerated owing to the richness of this collateral bed.
Liver
Occlusion of the common hepatic artery results in reversal of flow in the gastroduodenal artery from the pancreaticoduodenal and gastroepiploic arteries. The left gastric artery can also provide collateral supply through the right gastric artery (see Fig. 11-5 ). The right gastric artery is an important collateral in the setting of proper hepatic artery occlusion. Over time, small unnamed collateral arteries may form in the porta hepatis. Within the liver parenchyma, the right and left hepatic arteries have a rich potential collateral network ( Fig. 11-10 ). Occlusion of intrahepatic arterial branches is well tolerated for this reason.
The liver can recruit arterial supply from phrenic, intercostal, and internal mammary arteries. This is most often encountered in the setting of a vascular liver tumor.
Superior Mesenteric Artery
The collateral pathways to the SMA from the celiac artery branches are described above (see Celiac, this section). The other major collateral pathway is from the IMA ( Fig. 11-11 ). The ascending branch of the left colic artery communicates with the left branch of the middle colic artery at the splenic flexure through the arcade of Riolan. The marginal artery of Drummond also joins the left branch of the middle colic artery at the splenic flexure (see Fig. 11-9 ). Rarely, the dorsal pancreatic artery has a branch that continues to the transverse colon. Unnamed retroperitoneal collaterals from the aorta to the SMA can develop in some patients.
Inferior Mesenteric Artery
In the setting of IMA occlusion, the left branch of the middle colic artery is the major source of collateral blood supply. In addition, the anterior division of the internal iliac artery can supply the left colon through the hemorrhoidal arteries. This pathway is extremely important in patients with IMA occlusion undergoing right hemicolectomy, in which the anastomosis between the middle colic artery from the SMA and the left colic artery from the IMA is disrupted. In patients with intact collateral pathways and slowly progressive occlusive disease, a well-developed hypogastric collateral bed can supply the IMA, SMA, and ultimately celiac artery.
Imaging
The proximal celiac artery and SMA are amenable to interrogation by ultrasound (color-flow and duplex ultrasound) in most patients. The IMA is difficult to image in some patients owing to the small size of the artery. The velocities and directions of flow within the celiac artery and SMA are essential elements of the study. Flow in the celiac artery and its major branches has a low resistance pattern. Peak systolic velocities greater than 200 cm/sec in the celiac artery origin is indicative of at least 70% stenosis. The baseline waveform in the proximal SMA is high resistance. A postprandial state induces a high-flow, low-resistance waveform in the SMA. A peak systolic velocity at least 275 cm/sec and end-diastolic velocities of at least 45 cm/sec have both been shown to be predictive of SMA stenosis. In expert hands, ultrasound has an 89% sensitivity and 92% specificity for identification of stenoses greater than or equal to 70% of the SMA. Retrograde flow in the common hepatic artery is the best predictor of hemodynamically significant celiac artery stenosis. Ultrasound is less successful in the evaluation of distal branches of the SMA.
Magnetic resonance angiography (MRA) has excellent sensitivity and specificity for visceral artery ostial and proximal disease ( Fig. 11-12 ). Three-dimensional (3-D) acquisitions in the coronal plane, centered on the aortic bifurcation, include the visceral arteries as well as the hypogastric artery origins. The ability to view vessel origins in multiple planes is useful when anatomy is complex or anatomic variants are present. Heavy calcification, metallic clips, and patient motion can cause artifacts. Small vessel disease is difficult to visualize with current technology.
Multidetector computed tomography angiography (CTA) of the visceral arteries, particularly with 64-channel equipment or better, can provide excellent depiction of even small visceral arterial branches. When performed for occlusive or inflammatory disease, the study should include a noncontrast scan. Heavily calcified plaque can be obscured by dense arterial opacification on contrast-enhanced sequences (see Fig. 10-23 ). Enhancement in the arterial wall is an important sign of vasculitis. Image postprocessing is essential to evaluate the visceral arteries (see Figs.11-1 and 11-13 ). In addition to blood vessels, CTA provides valuable additional information about the perfusion of the visceral organs and bowel that can contribute to the diagnosis.
Visceral angiography requires knowledge of a wide range of catheter shapes and guidewires. A quick fluoroscopic examination of the abdomen is useful in patients undergoing elective examinations with a history of recent oral or rectal contrast. Residual barium or Gastrografin in the colon may degrade the quality of the study. The best means of viewing the visceral artery origins is with a lateral aortogram. A pigtail catheter (4- to 5-French) should be placed with the tip at the T12-L1 vertebral interspace to visualize the celiac artery and SMA origins (see Figs. 10-7 and 11-2 ). A lower position (below the renal arteries) with a slight left posterior oblique angulation depicts the IMA origin. Selective catheters for the visceral arteries range from generic cobra shapes to complex curves designed for specific branch vessels. In general, vessels that arise with angles 45-100 degrees from the aorta can be engaged with simple curved selective catheters ( Table 11-3 ; see Figure 2-10, Figure 2-18, Figure 2-19, Figure 2-20 ). When the artery arises at an acute angle, such as the IMA, a recurved catheter is the best choice. Review of prior CTA and MRA data when available can guide catheter selection. Visceral vessels are easily traumatized by catheters and guidewires, so gentle technique is required at all times. Leading with the soft tip of a guidewire when pulling or pushing into a vessel reduces spasm and the risk of dissection (see Fig. 2-46 ). Coaxial microcatheters are almost always necessary for selection of small branch vessels for the reasons listed earlier (see Fig. 2-21 ). High-flow microcatheters that are designed for power injection of contrast at 2-3 mL/sec are very useful for super-selective visceral angiography.
Table 11-3
Injection Rates for Visceral Angiography
| Artery | Typical Catheters | Injection (mL/sec/total volume) | Filming |
|---|---|---|---|
| Celiac | Cobra-2, Rösch celiac, Sos Omni | 5-7/30-60 | 2-4/sec × 10 sec, then 1/sec |
| Splenic | Cobra-2, Simmons-2 | 5-6/30-50 | Same |
| Hepatic | Cobra-2, Rösch hepatic, Simmons-2 | 4-5/15-30 | Same |
| Left gastric | Simmons-1, Rösch left gastric, Cobra-2 (Waltman loop) | 3-4/6-16 | Same |
| Gastroduodenal | Cobra-2, Rösch celiac | 3-4/6-16 | Same |
| Superior mesenteric artery | Cobra-2, Rösch celiac, Sos Omni | 5-7/30-60 | Same; may require two injections with overlapping upper and lower fields to include all of bowel |
| Inferior mesenteric artery | Sos Omni, Rösch IMA Simmons-1 | 3-5/9-20 | Same; for gastrointestinal bleed, use left posterior oblique projection and include anal verge on image |
IMA, inferior mesenteric artery.
The left gastric artery represents a specific challenge for selective catheterization when the vessel arises from its normal location—the upper surface of the celiac artery. A recurved pull-down catheter such as a Simmons 1 or a Sos can be pulled into the celiac artery so that the tip is advanced beyond the left gastric artery origin. Continued downward traction on the catheter forces the tip upward against the superior wall of the celiac artery. As the catheter is withdrawn further, the tip moves retrograde along the superior wall of the celiac artery until the orifice of the left gastric artery is engaged. The Rösch left gastric catheter is used in a similar fashion. Another technique is to form a Waltman loop in the splenic or hepatic artery with a braided 4- or 5-French Cobra-2 catheter (see Fig. 2-17 ). Once formed, the looped catheter is slowly pushed into the aorta until the tip engages the left gastric artery orifice. Occasionally, a left gastric artery that arises close to the origin of the celiac trunk can be selected directly with an angled catheter and a selective guidewire.
Celiac artery injections can be filmed in the anteroposterior projection (see Fig. 11-4 B ). Delayed filming is useful for visualization of the splenic and portal veins. The right anterior oblique projection is useful for selective common or proper hepatic artery injections to visualize the intrahepatic arteries. Complete coverage of the SMA may require overlapping fields of view to ensure visualization of the splenic flexure and small bowel in the pelvis. Complete coverage of the IMA also frequently requires two injections to include both the splenic flexure and the anal verge. A left posterior oblique projection will open the sigmoid colon flexure.
Several measures can be taken to improve the quality of visceral angiograms. Adequate injection rates and volumes are essential to fill this vast vascular bed. Glucagon (1 mg intravenously) before injection of contrast decreases bowel motion artifact on digital subtraction angiography studies, but is relatively short acting. Outside of the United States, hyoscine butylbromide (20 mg intravenously) provides durable bowel paralysis without the central nervous system side effects of scopolamine. This can be repeated if necessary to achieve cessation of peristalsis. Lastly, a series of masks obtained during a single respiratory cycle provides optimal subtraction when extended filming of injections is required, because most patients will have difficulty holding their breath.
Acute Mesenteric Ischemia
Acute mesenteric ischemia is one of the most potentially devastating visceral arterial emergencies. A variety of causative mechanisms have been described ( Box 11-1 ). More than 50% of cases are due to embolic occlusion of the SMA, one fifth are caused by thrombosis of a preexisting stenotic lesion, one fifth occur during a period of low flow or hypotension (nonocclusive mesenteric ischemia), and about 5% can be due to mesenteric venous thrombosis. Acute occlusion of the SMA is tolerated poorly, even in the presence of a widely patent celiac artery and IMA with intact collaterals. Time is the primary determinant of survival for these patients. In most series, the mortality rate exceeds 60% without early and aggressive intervention. Delay in diagnosis equals death.
Box 11-1
Etiologies of Acute Mesenteric Ischemia
-
Embolus (cardiac or aortic source)
-
Thrombosis existing atherosclerotic lesion
-
Dissection (aortic or localized to visceral artery)
-
Cholesterol embolization
-
Low-flow state (nonocclusive mesenteric ischemia)
-
Vasculitis
-
Iatrogenic (e.g., low placement of intraaortic balloon pump)
-
Mesenteric venous thrombosis
The classic presentation of acute intestinal ischemia is sudden onset of generalized abdominal pain out of proportion to the physical findings. This scenario is particularly suggestive of acute mesenteric ischemia of embolic origin in patients with cardiac arrhythmias. The pain may also be subacute or stuttering in onset. Nausea, vomiting, and diarrhea are common subsequent symptoms. Despite the severe abdominal pain, bowel sounds remain present and peritoneal signs are absent until the ischemia is advanced. The development of peritonitis heralds sepsis, shock, and onset of multiorgan system failure. The white blood cell count may be elevated, but there are no laboratory tests specific for bowel infarction. Elevated serum lactate, amylase, and phosphate levels are found in many patients. Metabolic acidosis and a history of acute onset of abdominal pain should be considered highly suspicious for advanced acute mesenteric ischemia.
The patient’s prior surgical history should be reviewed, with particular attention to the details of vascular reconstructions and bowel resections. The difficulty in imaging many patients with suspected acute mesenteric ischemia is that usually several other possible diagnoses are being considered at the same time. The plain film findings of early acute mesenteric ischemia are nonspecific. Gas in the bowel wall or portal vein indicates bowel infarction and is a late sign. Contrast-enhanced CT scan is an excellent initial imaging modality that allows evaluation of arterial and venous structures, as well as the bowel wall ( Fig. 11-14 ). However, presence of oral contrast in the colon from the CT can degrade subsequent angiograms.
Conventional angiography remains an essential diagnostic modality in suspected acute mesenteric ischemia. A lateral aortogram should be obtained first to inspect the celiac artery and SMA origins ( Fig. 11-15 ). The classic findings of an embolus are contrast outlining a convex filling defect causing partial or complete luminal obstruction. An aortogram in the anteroposterior projection is valuable to assess the aorta and exclude associated renal artery emboli. Selective injection of the SMA to exclude peripheral pathology is mandatory if the origin is normal on the aortogram ( Fig. 11-16 ). Filming should continue through the portal venous phase to assess the patency of the SMV. Celiac artery and IMA injections may be performed if the SMA is normal, but rarely are these culprit vessels in acute mesenteric ischemia.
Large emboli may lodge at the SMA origin. As many as 85% of emboli will then progress distally in the SMA, usually stopping just beyond the origin of the first major branch. These emboli result in profound ischemia, because major potential collateral pathways (either from the celiac artery via the pancreaticoduodenal arteries or the IMA via the middle colic artery) are obstructed. Simultaneous embolization to other organs is common. When the clinical examination and radiographic findings suggest that bowel remains viable, catheter-based intervention may be considered. These include thrombolysis and suction embolectomy (see Fig. 11-16 ). In most patients, emergent surgical embolectomy or bypass with resection of any portions of nonviable bowel is necessary.
Thrombosis of a previously symptomatic or asymptomatic visceral artery stenosis may cause acute ischemia if collaterals are poorly formed or nonexistent. This tends to occur during episodes of hemodynamic stress or derangement, such as during acute myocardial infarction or severe dehydration. A heavily calcified aorta or SMA on CT is indicative of underlying atherosclerosis. Thrombolysis (catheter-directed) with subsequent angioplasty and stent can be attempted when full-thickness bowel ischemia has not occurred. Surgical bypass with resection of any portions of nonviable bowel remains the standard therapy in acutely ill patients.
Nonocclusive mesenteric ischemia is a syndrome of low flow in the SMA in the absence of a fixed lesion ( Fig. 11-17 ). Most often associated with acutely ill patients on multiple vasopressor agents or digitalis, it can also be seen in the setting of cardiogenic shock and sepsis. Mortality is very high, usually from the precipitating conditions rather than the bowel ischemia. At angiography, vasoconstriction of the SMA and its branches, often with interposed areas of normal-caliber vessel, is characteristic. Injection of a vasodilator directly into the SMA, such as nitroglycerin, may break the spasm and can be used as a diagnostic test. Direct infusion of papaverine (0.5-1 mg/min) can be used to treat spasm until the patient’s condition stabilizes. There is little role for surgical intervention in these patients.
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