Imaging and Radiological Interventional Techniques for Gastrointestinal Bleeding in Children

Imaging and Radiological Interventional Techniques for Gastrointestinal Bleeding in Children

Imaging and Radiological Interventional Technique~ for Gastrointestinal Bleeding in Children By John M . Racadio, Ayad K.M. Agha, Neil D. Johnson, and...

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Imaging and Radiological Interventional Technique~ for Gastrointestinal Bleeding in Children By John M . Racadio, Ayad K.M. Agha, Neil D. Johnson, and Brad W. Warner Cincinnati, Ohio Causes of pediatric gastrointestinal (Gil bleeding in children are numerous. The role of radiology in defining associated pathology, pinpointing the bleeding site, and intervening to control hemorrhage is discussed here. Barium studies, computed tomography (CT), and magnetic resonance imaging (MRII each may play a role in identifying the underlying pathology associated with the bleeding. The exact source of bleeding may be localized by means of nuclear scintigraphy as well as selective angiography. In cases of life-threatening or persistent hemorrhage, once a bleeding source is identified, the interventional radiologist may offer percutaneous transcatheter therapy with selective intraarterial vasopressin infusion or embolotherapy. Copyright © 1999 by W.S. Saunders Company

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HE ROLE OF RADIOLOGY in the evaluation and potential intervention of pediatric gastrointestinal GI hemorrhage has changed with improved imaging techniques and technological advancements in microcatheters and embolotherapy. The degree of involvement by the radiologist in the workup of the child with GI hemorrhage varies with referral patterns, but, in general, imaging is most commonly requested after negative endoscopy results, or for indeterminate causes or locations of bleeding. The role of interventional radiology has increased in the treatment of GI hemorrhage, especially in very ill patients who are poor surgical candidates. This broad overview first describes and illustrates imaging findings of some of the more common causes of pediatric GI bleeding, focusing mainly on barium contrast studies, nuclear scintigraphy, and angiography. Second, this report defines the role of interventional radiology in percutaneous trans catheter therapy. IMAGING

Plain Radiography, Computed Tomography, Magnetic Resonance Imaging

Patients with GI bleeding as a primary complaint or as part of a constellation of symptoms generally undergo a barium contrast study (barium swallow, upper GI study, small bowel follow-through, or barium enema) as the initial radiological evaluation. Findings on these studies can suggest a specific diagnosis, but nuclear scintigraphy and angiography also can directly localize the site of gastrointestinal bleeding. Sources of esophageal hemorrhage in the pediatric population that may be identified by single or air contrast barium studies include esophagitis, esophageal foreign bodies, and esophageal varices. Different etiologies of infectious esophagitis tend to have characteristic features. Seminars in Pediatric Surgery, Vol 8, No 4 (November), 1999: pp 181-192

Herpes esophagitis shows discrete, less than 5-mm focal ulcers; cytomegalovirus typically shows large ulcers, greater than 2 cm; and candidiasis shows plaquelike, reticular mucosal defects and abnormal esophageal motility. Foreign body ingestion by children is a common problem.l Coins and toys are the most frequently swallowed items, and the majority of these (80%) pass through the GI tract without complication. 2 Bleeding is more likely to occur with sharp-edged objects that have become chronically lodged in the esophagus. Plain radiographs of the neck and chest will show radiopaque foreign bodies. The barium swallow study may help identify nonradiopaque foreign bodies by showing a filling defect within the esophageal barium column or by showing associated edema from a chronically lodged nonradiopaque foreign body, some of which may actually erode into the soft tissues adjacent to the esophagus. 3 Bleeding esophageal varices are a complication of portal hypertension, which may result from extrahepatic presinusoidal obstruction (50% to 60%) or from hepatic parenchymal disease. 4 Extrahepatic portal vein thrombosis is usually idiopathic but has been associated with omphalitis, appendicitis, dehydration, sepsis, and umbilical vein catheters. Intrinsic hepatic parenchymal disease may result from biliary atresia, cystic fibrosis, hepatitis, alpha-I-antitrypsin deficiency, and other systemic disorders of childhood. Both types of portal hypertension, however, are prone to GI hemorrhage from varices and from congestive or hemorrhagic gastritis. Variceal hemorrhage in pediatric patients with portal hypertension most often occurs from esophageal and anorectal varices, although gallbladder5 and duodenal varices 6 also have been described. On the barium esophogram, varices appear as serpiginous, wormlike filling defects. Varices also can be detected on computed tomography (CT) scan and magnetic resonance imaging (MRI) where they show imaging characteristics of slowly flowing tortuous vessels (Fig 1). Despite prophylactic H2 blockers and omeprazole, bleeding gastric and duodenal ulcers still occur in chilFrom the Departments of Radiology and Surgery, Children s Hospital Medical Center, Cincinnati, OH. Address reprint requests to John M. Racadio, MD, Department of Radiology, Children s Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH 45229-3039. Copyright © 1999 by W.B. Saunders Company 1055-8586/99/0804-0003$10.00/0 181

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Fig 1. Coronal MRI shows cavernous transformation of the portal vein and multiple gastric and duodenal varices.

dren, especially high-risk patients such as bone marrow transplant and bum patients. Findings on the single- or double-contrast barium study will show the classic ulcer crater with surrounding edema (Fig 2). Malrotation with midgut volvulus is the single most urgent surgical emergency in the newborn period. 7 •s Although bilious emesis may be the most common presentation, 01 bleeding may be seen in patients with ischemic bowel. The upper GI will show an abnormally positioned duodenal jejunal junction and may show a "corkscrew" appearance of proximal small bowel spiraling inferiorly or just a "bird's beak" cut off if obstruction is complete. Ninety percent of intussusceptions are ileocolic and

Fig 2. Prone spot image from an upper GI shows a large postbulbar ulcer crater (arrow) with surrounding edema and dilatation of the second and third portion of the duodenum.

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usually present in the first 2 years of life with colicky abdominal pain and bloody stool in up to 60% of cases. 9 An air or hydrostatic (positive contrast) enema can not only diagnose but also potentially reduce the intussusception. Successful air contrast reduction rates approach 90% and are generally safe in the absence of perforation or peritonitis. 10 Air enema reduction has become increasingly more popular than hydrostatic reduction secondary to a decreased complication rate and lower morbidity in the rare event of bowel perforation. 11-13 Inflammatory bowel disease often presents with lower GI bleeding and diarrhea. Although the peak incidence of ulcerative colitis and Crohn's disease (granulomatous enteritis) is between 20 and 50 years, 15% to 20% of cases are diagnosed in children. 3 Double contrast barium enemas are preferable to single contrast enemas, especially in visualizing mucosal abnormalities early in the disease process. Typically, ulcerative colitis involves the rectum and extends proximally without skip lesions. Early changes of hyperemia and edema may show a granular mucosal pattern. Progressive disease involves superficial ulceration, which gives a stippling pattern or regenerating mucosa surrounded by ulceration, which gives a pseudopolyp appearance (Fig 3). Late changes of fibrosis and scarring lead to strictures and bowel shortening.

Fig 3. A granular mucosal pattern in the ascending colon, "collar button" ulcers at the inferior hepatic flexure (arrowhead), and pseudopolyps in the descending colon are findings of ulcerative colitis on this barium enema.

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In contrast, Crohn's disease or regional enteritis may have a discontinuous, patchy distribution , and although most commonly involving the small bowel, it can occur anywhere in the GI tract. Because Crohn's disease involves the entire thickness of the bowel wall, deep ulcerations may grow and fuse with each other giving the intervening mucosa an edematous "cobblestone" appearance. Spasm and later fibrosis may result in rigid featureless segments of bowel, and fistul a formation is common (Fig 4). CT and MRI are invaluable in evaluating extraluminal complications of Crohn's such as phlegmon and abscess formation . Immunosuppressed children such as bone marrow transplant patients are at risk for typhlitis and neutropenic colitis, which may present with lower GI hemorrhage and progress to ischemic necrosis. Although barium contrast studies and even plain radiographs may show bowel wall thickening, cross-sectional imaging is superior in its ability to show circumferential thickening and inflammation of the paracolic fat (Fig 5). Polyps can be broadly divided into (1) hamartomas, which are generally considered benign and (2) adenomas, which may be premalignant. Familial or hereditary polyposis syndromes are associated with both types of polyps (Fig 6). Juvenile polyps are hamartomatous pol-

Fig 4. Discontinuous narrowed loops of ileum are seen in this child with Crohn's disease.

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Fig 5. Oral and intravenous contrast-enhanced CT shows circumferential thickening of the cecum and inflammation of the paracolic fat in this patient with typhlitis. (Courtesy of Kathleen H. Emery, MD, Cincinnati,OH).

yps, comprised of stromal and glandular tissue covered by colonic mucosa. They cause rectal bleeding in more than 95% of cases,14 and the majority are single and found in the left colon and rectosigmoid. A double contrast barium enema in an adequately prepared bowel can readily identify these polyps (Fig 7).

Fig 6. Multiple polyps create filling defects throughout the entire colon in this 14-year-old patient with multiple familial polyposis.

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Fig 7. This double-contrast barium enema shows a large pedunculated juvenile polyp in the proximal descending colon.

Necrotizing enterocolitis is the most common GI emergency in premature infants and may present with lower GI bleeding. Plain films initially may only show an adynamic ileus and bowel wall thickening but may progress to pneumatosis intestinalis, portal venous gas, and pneumoperitoneum. Contrast studies generally are not indicated because plain films and clinical evaluation together can evaluate the need for surgical intervention. Nuclear Medicine

Nuclear imaging, when performed correctly, may be extremely helpful in localizing the site of GI or peritoneal bleeding. Nuclear imaging also may be used as a modality in determining which patients are likely to require aggressive therapy and which are likely to benefit from angiography.15 Radionuclide studies are extremely sensitive and can detect bleeding rates as small as 0.1 mL per minute. 16 The radiation absorbed dose to the patient is relatively low (within the range of an abdominal radiograph). 17 Gl Bleeding Scan

Two types of radio tracers can be used to perform gastrointestinal bleeding studies: a nonblood pool agent,

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which is cleared from the blood rapidly (technetium [Tc] 99m sulfur colloid), and a blood pool agent that circulates in the blood for hours (technetium-99m-Iabeled red blood cells).18 When 99mTc sulfur colloid is injected intravenously, the radioactive particles pass through the mesenteric vascular bed supplying the bowel before being cleared by the reticuloendothelial system of the liver, spleen, and bone marrow. Technetium sulfur colloid extravasates if there is a leak or tear in such vessels. This technique is exquisitely sensitive and can detect a bleeding rate as low as 0.05 mL/min. A major drawback in using 99mTc sulfur colloid is that the patient must be actively bleeding during the short window of approximately 15 to 20 minutes available between the injection and the clearance of the radiotracer. This results in a high incidence of falsenegative results.19 Hence, this once popular method is used rarely today. The preferred method of detecting GI bleeding in children is the use of technetium-labeled red blood cells (99mTc RBC).20 There are 2 methods: a modified in vivo and an in vitro technique. The modified in vivo method for 99mTc RBC scanning was the original method used for GI scintigraphy. The red blood cells react with stannous ion followed by technetium pertechnetate. The pertechnetate is reduced by the intracellular stannous ion, which results in a complex formation with hemoglobin. The advantage of this technique is that the tracer remains intravascular, and images can be obtained up to 2 to 3 hours after the injection, which is helpful in patients who are bleeding intermittently. The disadvantages of this technique are the low labeling efficiency of approximately 80% to 90% and the high background activity. This can be overcome by in vitro red blood cell labeling with the use of a commercially available kit ULTRATAG (Mallinckrodt, St Louis, MO). This method has the highest labeling efficiency, in excess of 97%.21 With this method approximately 5 mL of whole blood is drawn into a syringe with acid citrate dextrose to which stannous chloride is added. 22 Immediately upon reinjection, an initial blood flow study is followed by 5-minute frames for up to 2 hours (Fig 8). Computerized cinematic acquisition combines these frames creating a dynamic display of the scintigram, which improves localization and detection of the GI bleeding site. 23 Meckel's Diverticulum and Duplication Cysts

In 10% to 50% of cases, ectopic mucosa is present in a Meckel's diverticulum, and 85% of these are gastric mucosa.24 Clinical symptoms occur in about one fourth of the affected patients. 25 The most common presentation is painless rectal bleeding.26 Although a duplication cyst is a separate pathological entity, 15% to 20% contain gastric mucosa7 and thus can produce GI bleeding by a similar mechanism as a Meckel's diverticulum. Duplication cysts

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threshold is almost impossible to correlate clinically. One of the few articles in the pediatric literature regarding arteriography in GI bleeding states that it is likely that a greater rate of bleeding is necessary to see contrast extravasation in children, and in fact the investigators rarely saw extravasation except when there was difficulty in keeping up with the patient's blood loss by transfusion. 33 Arteriography is, however, advantageous over

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I Fig 8. Technetium-99m-labeled red blood cell study shows a small focus of radiotracer accumulation in the left lower quadrant (arrowheads) in this bone marrow transplant patient with a 3-day history of brisk GI hemorrhage_

A

also may present with acute abdominal pain and GI bleeding caused by intestinal obstruction or intussusception_ 25 The imaging evaluation is similar in both conditions_ Technetium-99m pertechnetate is rapidly and actively taken up by the normal gastric mucosa_ It also concentrates in functioning ectopic gastric mucosa within a Meckel's diverticulum or a duplication cyst (Fig 9A and B).27 The sensitivity in detecting ectopic mucosa is greater than 98%_ After technetium-99m pertechnetate is injected intravenously, a dynamic I-minute blood flow study is performed after the injection, followed by 5-minute serial images for 30 minutes. 28 Some investigators have advocated the use of pharmacological therapy for the enhancement of the gastric secretions with histamine (H2) antagonists,29 pentagastrin,30 and glucagon. 3l In most centers, pharmacological enhancement is only used if there is strong clinical suspicion after a negative initial study result Angiography

Demonstration of intraabdominal bleeding by selective arteriography of the celiac and superior mesenteric artery was first established experimentally in dogs in 1963. 32 This technique, performed experimentally under optimum conditions, was successful in demonstrating bleeding points of 0.5 mL per minute and above. However, this

B Fig 9. Technetium-99m pertechnetate is taken up by functioning ectopic gastric mucosa (arrows) within surgically proven cases of a Meckel's diverticulum (A) and an exceptionally long ileal duplication cyst (8). (Courtesy of Michael J. Gelfand, MD, Cincinnati, OHIo

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Fig 10. (A) CT scan without oral contrast in a bone marrow transplant child presenting with bleeding and fever shows focal high attenuation in a loop of small bowel in the left lower quadrant (arrow) consistent with acute hemorrhage. (S) Contrast injection through the superior mesenteric artery shows active extravasation into a loop of distal jejunum (arrow). (C) Subselective microcatheterization precisely defines the bleeding vessel. (0) Contrast injection after embolization with polyvinyl alcohol particles Uvalon 250 to 355 I'm) shows cessation of extravasation.

endoscopy in some cases because it does not require a great deal of patient cooperation, can be performed on critically ill patients, does not require special preparation, and an accurate diagnosis can be made despite the presence of active bleeding and large amounts of blood in the gastrointestinal tract. The advantage of arteriography over nuclear medicine is that it not only provides bleeding localization, but can also offer trans catheter therapy. Angiography should be used in cases of acute gastrointestinal bleeding not responsive to conservative medical

therapy with clinical evidence of active life-threatening hemorrhage and continued blood requirements of greater than 500 mL in 8 hours,34 or in cases in which endoscopy is not available, contraindicated, or inconclusive. 35 Most children stop bleeding, regardless of the source, before or early in their hospitalization. 8 Seventy-five percent of patients hospitalized for GI bleeding will stop bleeding with bed rest, sedation, volume replacement, or blood transfusion. 36 The uncommon cases of fatal bleeding tend to occur in patients with severe underlying systemic illness.

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Because GI hemorrhage is by nature intermittent, and relatively brisk active hemorrhage is needed for diagnosis, some angiographers have used provocative measures to stimulate bleeding when initial arteriography results are negative. Although this would appear to subject the patient to unnecessary risk, various protocols have been attempted in adults including intravenous heparin (1 ,000 U/lO kg body weight), which can then be reversed with protamine sulfate (10 mg neutralizes 1,000 U heparin), tolazoline, 25 to 50 mg over 20 seconds, then angiography 60 seconds later, or urokinase (20,000 to 30,000 U/min) plus tolazoline together. 37 Although arteriographic diagnosis and therapy have been reviewed extensively in the adult literature, little experience has been reported in children. In one published pediatric study, which involved 27 children, arteriography had an overall positive diagnostic rate of 64%, and a false-negative rate of 36%. In acute GI bleeding, diagnosis was correct in 71 % and falsely negative in 29%. In chronic or recurrent GI bleeding, arteriography was correct in 55% and falsely negative in 45%.33 These success rates are comparable to several adult series. 38-4o The only angiographic sign that is 100% diagnostic of acute GI hemorrhage is contrast extravasation into the intestinal lumen (Fig lOA-D). However, other angiographic signs can be useful in evaluation of some of the more common pediatric pathologies that cause GI bleeding. Arteriography of a Meckel's diverticulum may show clusters of small tortuous irregular arteries representing persistent vitelline arteries that originate from the distal superior mesenteric artery,41 a dense capillary stain caused by ectopic gastric mucosa,42 and a mesodiverticular band artery (an abnormal ileal artery passing to the antimesenteric border ofthe ileum).43The combination of these angiographic findings should suggest the diagnosis and direct surgicallocalization. Typhlitis can be identified by arteriographic signs such as hypervascularity of the cecum with intense blush, contrast filled superficial ulcers, and dilated ileal arteries and veins. 44 Neutropenic patients also have a high incidence of enteritis (cytomegalovirus infection, pseudomembranous colitis, graft-v-host disease, chemotherapyinduced mucositis), which can involve necrosis and ulceration of the epithelium leading to vascular injury in the lamina propria and resulting in GI bleeding. 45 This often is complicated by thrombocytopenia or dysfunctional platelets. Angiography in these patients typically shows diffuse hypervascular blush of the affected colon (Fig 11). A point source of hemorrhage is not always identified. Unlike adults, in whom angiodysplasia of the colon represents 40% of lower intestinal bleeding,46 the incidence is unknown but certainly less frequent in chil-

Fig 11. An 11-year-old burn victim presented with a 3-day history of bright red blood per rectum . Selective catheterization of the inferior mesenteric artery (lMA) shows intense vascular blush without definite contrast extravasation in the descending colon (arrow). Vasopressin infusion through the proximal IMA at 0.2 U/min for 12 hours was successful in stopping the patient's hemorrhage.

dren. 47 Angiographic criteria include abnormal vascular tufts in the intestinal wall, early-filling veins (4 to 5 seconds after injection), and dense, persistent, slowly emptying veins in the late phase of injection. 48 Although angiography is the most valuable method for diagnosing angiodysplasia, occasionally, no angiographic abnormality is detected, especially when the lesions are very small and the blood flow is sluggish.33 In contrast to the adult population in whom angiodysplasia tends to occur in the right colon and cecum, occurrence in the small bowel and left hemicolon are more common in children. 47,49 INTERVENTION

One of the main advantages of angiographic diagnosis of GI bleeding is the ability to perform trans catheter treatment after localization of the bleeding site. The two main trans catheter therapies are intraarterial vasopressin infusion and embolization. Initial clinical experience with the creation of a transjugular intrahepatic portosysternic shunt (TIPS) in children suggests that this procedure is technically feasible and as safe in children as in adults.50 Although a full discussion of TIPS in children is beyond the scope of this review, TIPS can aid in management of complications of portal hypertension in children (including varicele hemorrhage) especially in those patients needing temporary relief as a bridge to liver transplantation. 50

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Fig 12. Coaxial system consisting of a guiding catheter (large arrow) through which a microcatheter (small arrow), and microguidewire (arrowhead) can be introduced.

Vasopressin

Vasopressin, a naturally occurring hormone produced by the neurohypophysis of the pituitary gland, causes constriction of very small arteries, arterioles, and capillaries. Since the initial report of selective intraarterial infusion of a pharmaceutical preparation of vasopressin to control acute lower 01 hemorrhage,5! transcatheter therapy has gained wider acceptance as a first line means of management. This is in part because of a significant perioperative mortality rate reported with emergent surgery in adults with acute gastrointestinal bleeding. 52-54 Vasopressin treatment is most successful in cases of diffuse mucosal hemorrhage or bleeding from small vessels. 55 Profuse bleeding from larger vessels is less likely to be controlled by intraarterial vasopressin infusion, and embolotherapy is preferable.34.56-58 In the adult literature, vasopressin infusion is reported to achieve hemostasis in 70%-90% of cases,35.55,59 and rebleeding rates upon discontinuation of this therapy are reported to be approximately 20%.55 A vasopressin infusion technique established in the adult population consists of placing a catheter selectively into the bleeding artery (eg, proximal superior mesenteric

Fig 13. Close-up photograph of coil deployment shows the end of the wire pusher within the microcatheter (arrowhead), the tip of the microcatheter (small arrow), and the coil exiting the catheter tip (large arrow).

Fig 14. (A) Selective contrast injection of the superior mesenteric artery in a 8-year-old bone marrow transplant patient shows intraluminal contrast extravasation from a proximal jejunal branch. (B) Subselective catheterization pinpoints the bleeding vessel. (C) After polyvinyl alcohol and coil embolization, extravasation is no longer seen. (D) The patient died of fungemia approximately 2 weeks later. Gross photo of a segment of proximal jejunum shows a large subacute ulcer. (E) Low-power micrograph shows the ulcer crater with occluded artery (arrow) in base of ulcer. (F) High-power view of the distal artery (arrow) shows multiple polyvinyl alcohol particles occluding the vessel. (Pathology images courtesy of Kevin Bove, MD, Cincinnati,OH).

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Fig 14.

artery) and beginning vasopressin infusion at 0.2 U/min for 20 to 30 minutes. A repeat angiogram is then performed to evaluate the vasoconstrictive efficacy of this vasopressin infusion rate. If the repeat angiogram shows continued bleeding, the infusion rate is increased to 0.4 U/min for an additional 20 to 30 minutes. If bleeding is not controlled after 0.4 U/min infusion, increasing the

(Continued)

dose rate is not beneficial, and embolization or surgery should be considered. 34 If vasopressin therapy is successful in controlling bleeding, infusion is continued for up to 12 to 24 hours and then gradually tapered over an additional 12 to 24 hours. For children an appropriate vasopressin dosage has not been defined. One investigator has suggested that

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a dose of 0.1 to 0.4 U/minll. 73 m2 body surface area be used. 60 The patient should remain in the intensive care unit during vasopressin infusion. The antidiuretic side effects of vasopressin may appear within 6 to 8 hours after initial infusion causing decreased urine output and electrolyte imbalance. Water retention may be treated with furosemide. Potential serious complications of vasopressin infusion, which have been described in adults, include myocardial infarction, severe arrhythmia, or hypertension (4%), bowel ischemia-infarction (0.8%), peripheral vascular ischemia manifested by mottling and pain (0.5%), antidiuretic hormone effect of vasopressin (1 %), and catheter-related thrombosis, false aneurysm, or sepsis (2%).35 It may not be prudent to perform intraarterial vasopressin infusion after unsuccessful embolization because an increased rate of bowel necrosis has been described. 61 -63 Embolization

The other transcatheter treatment is embolization, and is used when initial treatment of brisk bleeding is not responsive to conservative measures or vasopressin infusion. One should wait at least 30 minutes after vasopressin infusion before attempting trans catheter embolization to avoid an increased risk of bowel ischemia. 34 Waiting 30 minutes for the vasoconstrictive affects to resolve will also minimize false-po~itive results after embolization. Indications for transcatheter embolization described in adult populations are upper GI bleeding or bleeding from large vessels eroded by gastric or duodenal ulcers. Embolotherapy produces more rapid control of hemorrhage and helps avoid problems of long-term catheter placement and the cardiovascular side effects of vasopressin. The two major embolic materials used in trans catheter embolization of gastrointestinal bleeding are particulate material (polyvinyl alcohol foam [Ivalon, Contour]) and coil emboli. Polyvinyl alcohol is an inert Food and Drug Administration-approved substance with particle sizes ranging from 100 to 1,000 microns. The particles block the smallest vessels that they impact against, causing an inflammatory response with fibroblast invasion and thrombus formation. 64 Coils come in many types and sizes and are made of either stainless steel or platinum and may include Dacron fibers to increase their thrombogenicity. Coaxial systems allow placement of microcatheters through diagnostic catheters to achieve a subselective catheter position for embolization (Fig 12). Although polyvinyl alcohol particles can be injected through these microcatheters with a tuberculin syringe, coils generally are pushed with special wire pushers through the microcatheters (Fig 13).

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Embolization of the left gastric artery is effective in gastric mucosal bleeding with little risk of gastric ischemia because of multiple sources of blood supply and a rich submucosal plexus interconnecting major arteries. Successful embolic control of gastric hemorrhage has been described by multiple investigators in the adult literature, and complications are rare. 58 In the past, embolization for GI hemorrhage was considered to be a second-line trans catheter alternative used only after an unsuccessful trial of vasopressin infusion. Now, in many cases of upper GI hemorrhage proximal to the ligament of Trietz, embolotherapy has been advocated as the primary method for transcatheter control of bleeding when the bleeding vessel can be subselectively catheterized, and the vascular anatomy is not prohibitive. 58 The most significant risks of transcatheter lower GI embolization are ischemia and infarction, the latter of which has been reported to occur in up to 20% of cases. 61 In response to these observations some interventional radiologists have advised extreme caution in embolizing distal to the ligament of Trietz, and many have advocated a relative proximal site for embolization and the use of temporary occluding agents such as 1 to 2 mm Gelfoam pledgets to minimize the risk of infarction. 65-69 The major concern is producing irreversible ischemia based on the relatively sparse and poorly anastomosing mural arterial network ofthe colon. 70 )1 As catheter technology has improved, newer and smaller caliber catheters have enabled more subselective catheterization of distal vessels (Fig 14 A-F). In one of the first series of subselective embolization of large bowel, polyvinyl alcohol particles (100 to 590 Ilffi in size) were injected at the level of the arteria recta in 9 patients, and there were no cases of intestinal infarction induced by the procedure, and only 2 endoscopically proved incidents of asymptomatic mucosal ischemia. 61 The role of embolization of small bowel hemorrhage remains unclear because of reports of significant incidence of small intestine infarction induced by embolization. 58 ,72-74 However, many of these cases were in patients in whom embolotherapy was performed shortly after vasopressin infusion, which may have had lingering vasoconstrictive effects on collateral circulation. 75 From an anatomic viewpoint, the level of small bowel embolization in the mesenteric artery is quite criticaI.75 To avoid bowel infarction, the ideal embolization site is that which occludes only one of the nearest arcade of the vasa recta of the segmental branch such that the vasa recta itself is not occluded (Fig 15).15 Collateral circulation develops via arterial arcades distal to the occlusion and longitudinal communications between mural branches of vasa recta within the wall of the small intestine. The goal of

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performed, and no patient experienced bowel infarction. 75 CONCLUSION

Fig 15. Schematic small intestine vasculature with arrow shows the ideal point of small bowel embolization. (Courtesy of Glenn Miiiano, Cincinnati. OHIo

embolization in small intestinal hemorrhage is to reduce pulse pressure, allowing spontaneous hemostasis.?5 In a series of 6 patients suffering from life-threatening small bowel hemorrhage, this superselective embolization was

A barium contrast study usually is the first imaging modality performed in evaluation of a child with GI bleeding. Alone, or in conjunction with CT or MRI, a specific cause occasionally may be diagnosed. Nuclear scintigraphy is an excellent choice for physiological imaging of the GI tract and in many instances provides adequate anatomic localization of the source of bleeding. The main advantage of angiographic diagnosis of GI bleeding is the ability to perform trans catheter treatment following localization of the bleeding site. In one of the few reports of transcatheter therapy in children, intraarterial vasopressin infusion or embolization was attempted in 6 patients actively bleeding during arteriography with demonstrated success in 3 (50%).33 It is difficult from this small sample to draw general conclusions concerning the overall efficacy of transcatheter therapy. However, with continuing advances in microcatheters and embolization techniques, the role of trans catheter therapy in the treatment of GI hemorrhage will likely increase.

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