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The multifaceted role of radiology in small bowel obstruction
The Multifaceted Role of Radiology in Small Bowel Obstruction Kumaresan Sandrasegaran, M.D., Dean D. T. Maglinte, M.D., Thomas J. Howard, M.D., Frederick M. Kelvin, M.D., and John C. Lappas, M.D. Small bowel obstruction is a common clinical condition, often presenting with signs and symptoms similar to those seen in other acute abdominal disorders. The diagnosis and treatment of this dynamic process continues to evolve. The imaging approach in the work-up of patients with known or suspected small bowel obstruction and the timing of surgical intervention in this disease have undergone considerable changes over the past two decades. This article examines the changes related to the use of imaging technology in the diagnosis and management of patients with small bowel obstruction. The meaning of frequently used but poorly defined terms in describing intestinal obstruction is clarified and illustrated. © 2003 Elsevier Inc. All rights reserved.
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MALL BOWEL obstruction (SBO) is a common clinical condition, which accounts for about 12%-15% of acute abdominal admissions.1 History and physical findings are often suggestive of the diagnosis, which is straightforward when the classic picture of crampy abdominal pain, bilious vomiting, and abdominal distension is present. Plain abdominal radiographs in this setting often show multiple air fluid levels within dilated loops of small bowel, accompanied by a reduced amount of colonic gas. In many cases of confirmed SBO, however, the clinical picture is frequently vague. Plain radiography is often unhelpful, and the diagnosis may be in doubt. In these situations a routine abdomino-pelvic computed tomography (CT), fluoroscopic enteroclysis, or the combined study of CT and enteroclysis (CT enteroclysis) should be considered. Even when the diagnosis of SBO is unequivocal, further imaging may be required to identify the cause, site, and severity of the obstruction, and to determine whether bowel ischemia has developed. Specific radiological findings can often impact directly on the decision of whether a trial of nonoperative therapy can be safely undertaken or whether urgent surgical intervention is required. The radiologist may also aid clinical management by taking responsibility for the insertion of long naso-jejunal tubes to decompress the distended small bowel. In this article, we discuss the various imaging techniques to assess SBO, the features of complicated SBO, diagnostic clues to ascertain the etiology of SBO, and outline the role of the radiologist in the investigation and management of SBO. ABDOMINAL RADIOGRAPHY
The accuracy of abdominal radiography (AR) in diagnosing SBO is 50%-60%.2-6 In up to 10% of
cases, the information it supplies may be misleading.4 Improvement in the accuracy of AR begins with the consistent use of well-defined terminology. The term “nonspecific bowel gas pattern” is a time-honored descriptive phrase of variable meaning. It has been used to imply normality and abnormality, as well as uncertainty, as to the nature of any abnormality.5,7 The following terminology has been suggested to describe small bowel gas patterns to clarify imprecise or poorly understood terms in AR.8 1. Normal small bowel gas pattern: up to four loops of small bowel less than 2.5 cm in diameter and with normal distribution of gas and feces in nondistended colon. 2. Abnormal but nonspecific gas pattern: three or more air fluid levels in small bowel on horizontal beam films, with at least one loop distended to more than 3 cm, and colon either normal caliber or borderline distended. This appearance may represent either low-grade SBO or adynamic ileus and may require further evaluation by barium enteroclysis or CT enteroclysis (Fig 1). 3. Probable SBO pattern: multiple gas- and fluidfilled loops of distended small bowel with a moderate amount of colonic gas. It may be seen
From the Departments of Radiology and Surgery, Indiana University School of Medicine, Indianapolis, IN; Department of Radiology, Methodist Hospital of Indiana, Indianapolis, IN. Address reprint requests to Dean D. T. Maglinte, M.D., Department of Radiology, Indiana University Medical Center, 550 N University Boulevard, University Hospital, Indianapolis, IN 46202-5257. © 2003 Elsevier Inc. All rights reserved. 0887-2171/03/2905-0000$30.00/0 doi:10.1053/sult.2003.0000
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Fig 2. Probable SBO pattern. (A) Supine abdominal radiograph of an elderly female with recurrent abdominal pain, prior pelvic surgery, and external radiation for endometrial carcinoma shows moderately distended gas and fluid-filled loops of small bowel (arrows) and some gas in segments of colon. (B) Axial CTE image shows stricture (straight arrow) and dense mesenteric adhesions (arrow heads) fixing loops of small bowel with dilatation of proximal loops.
Fig 1. Abnormal but nonspecific gas pattern. (A) Upright abdominal radiograph of a middle-aged patient with recurrent abdominal pain and prior appendectomy shows multiple mildly dilated pelvic loops of ileum with air fluid levels (arrow) and normal gas distribution in colon. (B) Radiograph obtained during single contrast phase of enteroclysis shows dilated loop of small bowel in pelvis with abrupt cutoff (arrow). Further infusion showed contrast in normal distal ileum (not shown). Surgery confirmed dense adhesive band obstruction.
in early complete SBO, partial high-grade SBO, or adynamic ileus. These patients should ideally have a CT examination and if this is inconclusive a CT enteroclysis should be entertained, especially in patients with multiple prior abdominal surgeries or radiation (Fig 2). 4. Definite SBO: Dilated fluid-filled loops of small bowel with a gasless colon. This is diagnostic for SBO, and in our institution an emergent CT is usually obtained to assess for strangulation. In the absence of strangulation, following partial decompression, barium enteroclysis or CT enteroclysis can be done if further characterization of the severity or
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etiology of obstruction is clinically warranted (Fig 3). A study assessing 81 patients9 with varying degrees of SBO showed that the presence of differential air-fluid levels in the same loop of bowel and a mean air fluid level of more than 25 mm on erect AR strongly suggests high-grade rather than low-grade obstruction. In this study, the classic string of beads sign did not reliably differentiate between high- and low-grade obstructions. Despite some accuracy in making the diagnosis of SBO, AR is notoriously poor at determining the site and etiology of SBO (Fig 4). BARIUM RADIOGRAPHY
Barium does not inspissate in an adynamic gut and, therefore, can be administered orally to evaluate SBO. Because orally ingested iodinated water soluble contrast agents are hypertonic and have poor mucosal coating, they are best not employed for the oral evaluation of SBO.10 Barium examination without intubation is used in centers where expertise for enteroclysis (EC) is not available. These oral small bowel follow-through studies are time consuming, and often fail to accurately demonstrate the site of obstruction. Further, retention of barium above a high-grade obstruction often delays subsequent performance of CT. EC, on the other hand, is a minimally invasive procedure and is best performed with conscious sedation of the patient. Barium EC can correctly predict the presence, level, and cause of obstruction with an accuracy of 86%-100%.11 By EC criteria, the upper limits of caliber for jejunum and ileum are 3 cm and 2.5 cm, respectively. The diagnosis of SBO is made by identifying a transition zone characterized by a distinct change in caliber. The degree of SBO is graded based on objective criteria proposed by the Indiana group as follows:11 1. Low-grade partial 2. High-grade partial 3. Complete In low-grade partial SBO, there is little or no delay in arrival of contrast to the transition zone, and there is sufficient passage of contrast material to delineate the mucosal pattern of post-obstructive bowel. In high-grade partial obstruction, only a small amount of dilute contrast material is seen to traverse the transition zone. EC is usually not necessary in suspected complete SBO unless the
Fig 3. Definite SBO pattern. (A) Upright abdominal radiograph of an elderly patient with prior pelvic surgery shows air fluid levels in moderately distended small bowel loops (arrows) and feces in nondistended colon. (B) Following overnight long tube decompression, barium enteroclysis shows dense adhesive band obstruction (arrow) in a loop of ileum in upper pelvis.
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CT are its ability to distinguish low-grade SBO from normalcy, and to assess patients who may be harboring more than one site of obstruction. It is possible to combine some of the advantages of both techniques with the hybrid technique of CT enteroclysis. In our institution, it is usual to perform CT enteroclysis using water-soluble contrast instead of fluoroscopic barium enteroclysis in situations of incomplete SBO, unless it is considered important to also demonstrate mucosal detail, as may be the case in Crohn’s disease. CT CT has become an important tool in the preoperative assessment of patients with SBO. Early studies focused predominantly on patients with high-grade obstruction. These reports found a sensitivity of 78%-96% and accuracy of about 90%95%.12-14 Later studies, which included lower grades of SBO, reported an overall sensitivity and accuracy of 63%-66%.15 This lower accuracy is because of the poor sensitivity of CT in evaluating patients with low-grade SBO (48%-50%).2,15,16 However, it remains accurate for high-grade partial and complete SBO. CT Technique
Fig 4. Unreliability of abdominal radiography in determining the site of obstruction. (A) Supine abdominal radiography of an elderly patient with nausea and vomiting shows disproportionately dilated loop of jejunum (arrow) and a few mildly distended loops more distally. (B) Radiographs obtained during single contrast phase of a barium enteroclysis shows dense adhesive band obstruction (arrow) in a loop of distal ileum in right upper pelvis.
patient has a history of complex abdominal surgery. If performed, there will be no passage of contrast beyond the obstruction on delayed radiographs. The main advantages of EC over routine
There is no consensus as to whether oral contrast material is necessary. Arguments against the use of positive oral contrast material have focused on the risk of vomiting, delay in diagnosis, and lack of progression of the orally ingested material because of the obstruction. Furthermore, the reduction of contrast between intestinal lumen and wall makes measurement of the thickness of the small bowel wall more difficult. In the era of multichannel CT, dense oral contrast material may interfere with image reconstruction. We do not usually use positive oral contrast material when high-grade SBO is suspected, but it may be useful in appreciating mesenteric fluid collections and may show the transition zone better in low-grade obstructions. The positive contrast material may be either a 1.2% solution of barium or a 2% solution of iodinated water-soluble contrast. It is routine practice to give intravenous contrast in patients with SBO unless there are contraindications to its use. With multichannel CT scanners, a slice width between 5 mm and 7 mm is used, with approximately 50% overlap reconstruction. If necessary, the raw data can be reconstructed at thinner slices at the suspected
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transition zone. Our experience is that the diagnostic confidence is improved if soft copy images are reviewed on a workstation using cine scrolling. This technique includes the ability to perform instantaneous multiplanar reconstructions (MPR). We find that MPR is particularly useful in finding the transition zone of SBO or identifying internal hernia and closed loop obstruction. CT Diagnosis To diagnose SBO, a transition zone between dilated small bowel (⬎2.5 cm) and normal caliber small bowel must be seen (Fig 5). Diffusely dilated small bowel or air fluid levels are not reliable in distinguishing adynamic ileus from mechanical SBO. The presence of fecal matter in small bowel, the small bowel feces sign, is abnormal. This finding is usually seen in patients with chronic SBO. Uncommon causes of this sign in the absence of SBO include infectious enteritis and over-vigorous jejunal tube feeding.17 The site of obstruction has therapeutic implications. Proximal SBO is more likely to resolve nonoperatively than distal ones.18 CT has been found to be about 94% accurate in assessing whether or not a SBO is proximal in location.3 Difficulties arise if bowel loops are not meticulously followed since jejunum may lie in the pelvis and ileal loops may lie in the upper abdomen, especially if there is prior surgery. The classification of low-grade, high-grade partial, and complete SBO is used, although this determination is harder to make with conventional CT compared to enteroclysis. CT Enteroclysis CT enteroclysis (CTE) has been promoted because it is a hybrid procedure that combines the advantages of CT and EC into a single test. The former allows 3D acquisition and global assessment of bowel wall and mesentery, whereas the latter allows better recognition of mucosal detail and the diagnosis of low-grade SBO. CTE does have its disadvantages, the foremost of which is the need for placement of a nasoenteric tube. If CTE is performed with neutral oral contrast, such as water, intravenous contrast may be given. The procedure of CTE is described elsewhere.19 Our group analyzed 92 patients with documented SBO who had both CT and CTE during the diagnostic work-up; sensi-
Fig 5. Conventional abdominopelvic CT in SBO. (A) Axial image at the level of the kidneys shows abrupt transition in the caliber of small bowel loops and collapsed or normal caliber small bowel loops indicating transition zone (arrow). Assessment of bowel wall perfusion is possible with intravenous contrast and a neutral oral contrast such as water. (B) Barium enteroclysis performed the following day confirms transition zone in right hemi-abdomen anteriorly (arrow), proven to be a dense adhesive band at surgery. Note collapsed loops distal to transition point.
tivity rates of 60% for conventional CT and 98% for CTE were recorded.20 Of the 19 false-negative cases recorded by conventional CT, 17 were found to be low-grade SBO on CTE (Fig 6).
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Fig 6. CTE. Why bother? (A) Axial image of conventional CT at level of upper pelvis of an elderly woman with symptoms of SBO and prior hysterectomy shows multiple diverticula in sigmoid. Small bowel loops are of normal caliber. (B) Axial image at level of lower pelvis shows normal appearance of posterior vaginal cuff (arrow). (C) CTE, performed because of persistent symptoms, shows mildly dilated loops of ileum because of anterior peritoneal adhesions (arrows) and nondistended distal ileum indicating low-grade SBO. In addition, a sinus tract is opacified, leading to a small fluid collection (arrowhead) consistent with a small diverticular abscess. (D) Image at level of lower pelvis shows fistulous communication with the posterior vaginal cuff, indicated by presence of infused enteral contrast (arrow).
Barium enteroclysis is known to be of value in diagnosing lower grades of SBO but does not give information on extra-intestinal manifestations of disease. Traditionally, barium enteroclysis and CTE have been shown to be of similar accuracy in low-grade SBO.21 It is not clear if CTE using a
multichannel CT scanner is superior since it allows for thinner slice width. In addition, many surgeons are reluctant to allow use of barium in patients who may be surgical candidates. CTE is less operatordependent and provides uniform results over a wide spectrum of patients.22
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Table 1. Advantages and Disadvantages of Sequences Used in MRI Enteroclysis Sequence
HASTE
Advantage(s)
1. 2. 3. 1. 2.
true FISP
T2 w TSE
T1 w post gadolinium series with fat saturation
Disadvantage(s)
Reduced susceptibility artifact No black boundary artifact High lumen to wall contrast Insensitive to motion artifacts High contrast between lumen and wall
1. Good soft tissue contrast-lesion characterization 2. Reduced black boundary and susceptibility artifact 1. Assessment of vascularity of bowel wall 2. Good contrast resolution
MRI AND MR ENTEROCLYSIS
MRI has not been extensively used to assess bowel disorders. With increasingly fast sequences, many now completed within a single breath-hold, it is now possible to image the entire abdomen and pelvis within 10 minutes. Typical sequences used are half-Fourier single shot turbo spin-echo (HASTE), true fast imaging with steady state precession (true FISP), and gadolinium-enhanced fat saturated T1-weighted volume acquisition (VIBE, 3D FLASH, or FAME). Each sequence has its advantages and disadvantages (Table 1). A recent study based on 25 patients reported that HASTE imaging in 3 planes was superior to helical CT in diagnosing SBO,23 however, there was no mention of the severity of the SBO. These findings remain to be confirmed by other authors. Currently, MR methods of examination are not part of the routine evaluation of SBO. COMPLICATED OBSTRUCTION
An important question to be answered during the imaging of SBO is whether the obstruction has been complicated by the development of ischemia. The radiologist, therefore, needs to be familiar with the CT features of closed loop obstruction and strangulation. Closed Loop Obstruction Closed loop obstruction (CLO) occurs when a variable length of small bowel is obstructed at both ends leaving a segment that is unable to be decompressed. This situation is seen in approximately 10% of SBO. The mortality of this complication
1. Sensitive to flow artifact (reduced by intravenous glucagon) 2. Poor visualization of mesentery 1. Black boundary artifact, cannot determine wall thickness (reduced with fat suppression) 2. Sensitivity to susceptibility artifact 1. Susceptible to motion artifact
1. Reduced spatial resolution 2. Fat containing stool may mimic enhancing lesion (overcome by subtracting post- from pregadolinium series)
can be as high as 35% and rises sharply if diagnosis is delayed by more than 36 hours. The importance of CLO lies in the high incidence of associated strangulation, as the obstructed loop is free to rotate along its axis. Importantly, clinical signs are often inconclusive. Studies in which CT was not used as an integral part of the diagnostic pathway preoperatively diagnosed CLO in only 50%-80% cases.24-28 CLO is usually caused by adhesions or hernias. CT signs of CLO depend upon the 3D orientation of the obstructed loop and have been well described by Balthazar:29,30 1. If the loop is horizontal, CT shows a distended fluid-filled C or U shaped loop with engorged mesenteric vessels. The two ends of the distended loop come together. 2. If the bowel is more vertically orientated, the diagnosis is slightly more difficult. Recognition depends on appreciating fluid-filled loops radiating away from the sites of obstruction. Coronal and sagittal reconstructions help increase diagnostic certainty. 3. At the site of obstruction, the collapsed loops may be oval or triangular. 4. A beak sign may be seen, caused by the gradual tapering of the afferent and efferent limbs near the point of obstruction. 5. The proximal bowel is likely to be distended, to a lesser degree than the closed loop that is typically filled only with fluid. The distal bowel is nondistended. The sensitivity of CT diagnosis for CLO is about 85%.30 Barium enteroclysis has been shown to
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Fig 7. Multichannel CT enteroclysis of closed loop obstruction. (A) Radiographic phase of a CTE with positive enteral contrast in a patient with renal transplant and prior surgery for SBO shows the tip of the enteroclysis catheter in the distal duodenum. The proximal jejunum is dilated secondary to a linear defect (arrow). The loop of jejunum distal to the linear defect is also dilated (arrowhead). The radiograph was obtained in the right posterior oblique position. (B) Coronal and (C) axial image at level of balloon shows the distended limbs of the involved segment (arrowheads). (D) Axial image at a lower level shows the dense mesenteric adhesive band (arrow) producing the closed loop obstruction. Contrast is seen in the dilated duodenum. (D) Closed loop obstruction from adhesions without evidence of strangulation was confirmed at surgery.
demonstrate closed loop configuration in lowgrade obstruction. In our recent experience, multichannel CTE simplifies the demonstration of closed loop configuration of SBO (Fig 7). Strangulating Obstruction The various manifestations of strangulation have been recently reviewed by Ha.31-33 Strangulation
can occur in closed loop obstruction or, less commonly, in simple obstruction where the pressure of luminal distension causes impairment of venous drainage. Volvulus because of congenital malrotation or primary small bowel volvulus, as seen in African patients, is a rare cause of strangulation. CLO does not equate to strangulation and merely signifies incarceration, which may be reversible.
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Strangulation is found in about 10%-15% of patients undergoing surgery for SBO,27,30 and is associated with a mortality of 20%-30%.27,28,34,35 The diagnosis is usually not made on clinical grounds. Before routine use of CT, up to 85% of patients with the surgical finding of strangulated small bowel were not correctly diagnosed preoperatively.30 The recognized CT findings30,32,36 in early strangulation include wall thickening, target or halo appearance because of submucosal edema, mesenteric vessel engorgement, and ascites. More advanced ischemia is heralded by mesenteric vessel blurring, hemorrhagic ascites, enhancement of thickened wall on delayed images, pneumatosis, and mesenteric or portal venous gas (Fig 8). In earlier studies, the sensitivity of CT in detecting ischemia was reported between 60%80%.30,37-39 A study with faster helical CT scanning has shown a higher accuracy of 95%,36 likely related to the better contrast bolus achievable with such scanners. It is possible to detect reduced early enhancement of bowel wall as a highly specific sign for ischemia. With current multichannel CT it is probable that diagnostic confidence of assessing bowel vascularity will be even better.40 To our knowledge, no large studies have been published using dual or triple phase examinations of small bowel to detect abnormal enhancement patterns. Differential diagnosis of small bowel wall edema and mesenteric inflammatory changes include bowel hemorrhage or focal inflammation. The findings of impaired vascular enhancement and bowel obstruction make strangulation the more likely cause of this appearance. SBO vs. Adynamic Ileus In ileus, there is usually distension of both small and large bowel. However, in generalized ileus, the colonic distension usually predominates. In some patients, particularly in those with peritonitis, there is variable distension of the proximal colon with a nondistended left colon. This should not be mistaken for mechanical obstruction in the proximal colon (Fig 9). The best CT sign of SBO is the presence of an identifiable transition zone in the small bowel. Early studies have suggested CT is 100% accurate in differentiating the two conditions.41 However, these authors reflected that this may represent an unduly high figure,2 an opinion with which we concur. If CT findings are equivocal, CTE often yields the correct diagnosis.
Fig 8. Strangulating obstruction. (A) Axial CT image of mid-abdomen in 76-year-old patient with strangulating obstruction shows gas within linear mesenteric structures consistent with mesenteric venous gas (arrow). Gas is seen adjacent to intravenous contrast opacified vascular lumen. (B) Axial CT at a lower level shows air in dependent wall of small bowel loop (pneumatosis) (arrows) and free peritoneal air (arrowheads).
ETIOLOGY OF SBO
The three most common causes of SBO in the western world are (1) adhesions, (2) Crohn’s disease, and (3) neoplasm.20 Hernia used to be an important etiology of SBO, but early detection and
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tory of abdominal surgery.44 The diagnosis of adhesions is presumed on CT if there is a narrow zone of transition without an identifiable obstructive lesion. The characteristics and location of adhesions are easily demonstrated by CTE (Fig 10). In our experience, CTE with positive enteral contrast is the best method of characterizing adhesions, particularly in patients with recurrent lowgrade partial SBO. External Hernia Indirect inguinal hernia is the commonest hernia. It is clinically obvious, but CT may be helpful in obese patients or those with inguinal scars. Femoral hernias may be notoriously difficult to identify clinically but are fairly obvious on a good quality CT. CT is also useful for other external hernia, such as obturator hernia, which are difficult to diagnose and have a mortality as high as 25%.45 Internal Hernia
Fig 9. Difficulty in differentiating SBO and adynamic ileus. (A) Axial CT image of mid-abdomen in a patient with renal failure and peritonitis shows distention of small bowel but right colon is collapsed (arrows). The appearances suggest mechanical distal SBO. However, no clear transition zone is seen. Ascites is present. (B) A second CT scan two days later shows right colon is now of normal caliber (arrow) indicating the bowel changes were ileus secondary to peritonitis.
In internal hernia, unlike the external variety, the bowel herniates through the peritoneal covering and lies trapped within the abdominal cavity. The risk of strangulation or obstruction is substantial. The locations of these types of internal hernia include left and right paraduodenal, foramen of Winslow, transmesenteric, transomental, and paracecal. A complete discussion of CT features of internal hernia is beyond the scope of this article, and the interested reader is referred to specific
more aggressive elective repair has led to a considerable decline in the prevalence of hernia-induced SBO. In developing countries, hernia remains an important cause of SBO. The CT findings of different causes of SBO are discussed below. Adhesions Adhesions cause about 50%-75% of SBOs.42 They arise from prior surgery in most cases. Ninety percent of patients undergoing abdominal surgery have been found to have adhesions on subsequent laparotomy; most of these are not obstructing.43 Adhesions may also be congenital or occur following abdominal inflammation such as pelvic inflammatory disease or endometriosis. Thus, 10% of adhesions are found in patients without prior his-
Fig 10. SBO because of adhesions in a patient with abdominal malignancy. Dense adhesive band obstruction in a patient with known metastatic liver disease from carcinoid (not shown) suspected of having abdominal carcinomatoses. A smooth transition point in the anterior abdomen (arrow) is seen consistent with adhesive band obstruction. (Reproduced with permission from Maglinte, et al.)
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Crohn’s Disease
Fig 11. Left paraduodenal hernia. Axial CT of a 48-year-old woman shows small bowel loops (white arrow) between stomach (S) and pancreas (P), lying behind a branch of inferior mesenteric artery (black arrow). Patient presented with recurrent abdominal pain. An incarcerated left paraduodenal hernia was confirmed at surgery.
texts.46,47 The commonest type of internal hernia is a left paraduodenal hernia. However, with the increasing incidence of complex abdominal surgery, such as Roux-en-Y gastric bypass, transomental hernia is becoming more widespread. In left paraduodenal hernia there is herniation of the 4th part of the duodenum and proximal jejunum through a defect in the posterior peritoneum and the confluence of small bowel mesentery, transverse, and descending mesocolon. Half are present with acute or subacute obstruction. The classic finding is of dilated loops of jejunum in a rounded configuration between the inferior mesenteric vein, which forms an antero-superior border of the neck of the hernia, and the ascending left colic vein that forms the inferior border. There may be pressure effect on the posterior stomach (Fig 11). In obstructed transmesenteric hernia, there is dilated small bowel anterior to the transverse colon without discernible omentum between small bowel and abdominal wall. Detection of internal hernia is not easy on CT. The key to diagnosis is identification of the abnormal position of the small bowel and the altered course of mesenteric vessels. However, unusual positions of small bowel and its mesentery may be encountered in asymptomatic postoperative patients because of incision of their peritoneal attachments.
The CT signs of active Crohn’s disease are well established.48 Signs of acute inflammation include the target appearance of bowel with enhancing mucosa and serosa, and edematous submucosa and the “comb” sign because of perienteric hyperemia. In the chronic situation, fibrofatty proliferation can be seen. Immune modulating drugs such as infliximab (Remicaid) have become important in reducing disease activity and treating fistulae. However, they may worsen pre-existing small bowel strictures leading to frank intestinal obstruction. In our experience, we find CTE performed with intravenous contrast and water or methylcellulose as neutral enteral contrast to be the most reliable technique for detecting inflammatory changes, and CTE with positive enteral contrast the optimal method in demonstrating stenosis and fistula (Fig 12). For a treatise on current concepts in imaging of Crohn’s disease, the reader is referred to a recent review article.48 Patients Treated with Cancer The cause of SBO in up to 40% of patients with known intra-abdominal malignancy is adhesions.6 Hernias, radiation enteritis, and neoplastic compression account for the remainder. EC is 88% accurate for differentiating adhesions from other causes of partial SBO in patients with known malignancy.49 CTE has been reported to be an excellent technique for assessing these patients (Fig 13).21 Intussusception Intussusception accounts for 5% of SBO in adults.50 CT appearances of small bowel intussusceptions vary, depending partly on the severity of the intussusception. A dilated loop of bowel containing an eccentric crescent of fat, representing the mesentery of the intussusceptum, is an early finding. There may be mild proximal obstruction. More advanced stages are depicted by a sausageshaped mass with alternating layers of low (mesenteric fat) and high attenuation (bowel wall). Obstruction will be evident by this stage. If diagnosis is delayed, a reniform mass may be seen with peripheral high attenuation of bowel wall and variable attenuation of the center of the mass because of ischemia, oral contrast, and bowel gas. The invaginated mesenteric fat may not be visible because of edema and necrosis (Fig 14).
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Fig 12. CTE in Crohn’s disease. (A) Abdominal radiograph of a 79-year-old patient with known Crohn’s disease shows massive distention of multiple loops of small bowel. (B) Supine abdominal radiograph following overnight gastric decompression with long tube shows decreased distention of small bowel loops. (C) Axial CTE image of lower abdomen following infusion of positive enteral contrast shows markedly distended small bowel proximal to a long segment of stenosis in distal ileum (arrow); C ⴝ cecum. (D) Axial image of upper pelvis shows a small fistula (arrow) between stenosed segment and sigmoid colon (S). (Reproduced with permission from Maglinte, et al.)
Obturation Obstruction Gall stone ileus is a rare condition seen predominantly in elderly females. It has a mortality of up to 27%.51 The classic plain radiographic constellation (Rigler’s triad) of SBO, pneumobilia, and ectopic gallstone is seen in only a third of cases.52
CT findings are similar, but the obstructing gallstone is more easily identified (Fig 15). Phytobezoar are impacted luminal masses containing indigestible food. They are more likely to occur in patients following gastrectomy or with autonomic neuropathy. The commonest site of ob-
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Drug Induced Enteropathy Nonsteroidal anti-inflammatory drug (NSAID) induced enteropathy is an uncommon cause of small bowel strictures. Typically, on barium radiography or CTE, multiple constricting diaphragms are seen (Fig 17). Patients usually have a history of taking NSAIDs for more than six months. The enteropathy can occur with rectal as well as oral preparations. The mechanism of small bowel mucosal damage is not clear. The findings on enteroclysis are well described but can be difficult to make if the radiologist is not aware of the clinical picture. Cystic Fibrosis Related SBO Fibrosing colopathy (FC) is a recently recognized complication in children and adults with cystic fibrosis (CF) and other patients taking pancreatic enzyme supplements.54-56 There is edema of the distal bowel wall leading to focal strictures (Fig 18). This has been described in the right colon in patients taking some, but not all, forms of pancreatic enzyme supplements. There is suspicion, not proven, that it may be related to the dose of enzyme, though other factors such as enteric coating may also be responsible. We are aware of the presence of multifocal intermediate length (approximately 5 cm) strictures of ileum in older
Fig 13. Value of CTE for assessing SBO in patients with malignancy. (A) Axial CTE image of an elderly patient with prior surgery for sigmoid malignancy. Partial obstruction secondary to serosal metastases (white arrow) is shown. Ascitic fluid and distended small bowel loops (black arrows) are present. Also note anterior peritoneal implants (curved arrow). (Reproduced with permission from Maglinte, et al.) (B) A 72-year-old man with sigmoid cancer treated with surgery and high-dose external beam radiotherapy. Nine months later he presents with constipation. CEA is normal. Proximal bowel loops are distended. There is wall thickening and stricture of a pelvic loop of ileum (arrow) consistent with radiation enteritis. No mass is seen. Also note radiation injury to sigmoid colon (curved arrow).
struction by a phytobezoar is the jejunum or proximal ileum.53 These masses have a fairly classic appearance on CT. Differentiation from small bowel feces, found in chronic SBO, may be difficult. Encapsulation, rounded configuration of mass, wall thickening, and mesenteric edema at the site of the mass are more likely to be associated with phytobezoar (Fig 16).
Fig 14. Intussusception. Axial CT image of 47-year-old male with acute abdominal pain shows a long segment of intussusception. The proximal limb shows bowel within bowel appearance (curved arrows). The mesentery of intussusceptum is edematous and has higher density (white arrows). The intussusception has a reniform appearance. The wall shows mixed density because of presence of oral contrast, edema, and hemorrhage (arrowheads). Hemorrhagic ascites (black arrow) is present. At surgery, 120 cm of small bowel with necrosis was removed. Surgical pathology did not show a lead point.
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Fig 16. Afferent loop obstruction with phytobezoar. A 29year-old morbidly obese patient underwent gastric Roux-en-Y gastric bypass 5 months previously. She presented with abdominal pain. The afferent loop ends blindly and should have been less than 10 cm long. However, a long afferent loop was fashioned in this patient, and the loop became obstructed with ingested plant material (arrows). The phytobezoar can simulate feces (see text).
Fig 15. CT “Rigler’s triad” of gallstone ileus. (A) Axial CT image of upper abdomen in elderly female patient with abdominal pain and vomiting shows small gallstone (black arrow) in gall bladder. Air in gall bladder and common duct (white arrows) is present. Note distended stomach (S). (B) A 2-cm laminated gallstone (black arrow) in ileum with dilation of proximal segment. Distal ileum is collapsed (white arrow).
addition to detecting the severity, location, and probable etiology of SBO, it is also useful in determining the presence of bowel ischemia or other explanation for the symptoms such as diverticulitis and appendicitis.
patients with cystic fibrosis. This “fibrosing ileopathy” may mimic Crohn’s disease but, histologically, granuloma are not seen. In our limited experience of this condition, we find that CTE has been superior to other methods of diagnosis. Water-soluble contrast media used for enteral infusion aids in the evacuation of inspissated secretions in the small bowel and colon. Other causes of SBO in CF patients include intussusception and distal intestinal obstruction syndrome (DIOS). The latter is similar to meconium ileus equivalent in children and is because of the presence of inspissated secretions (Fig 18). It is quite possible that “fibrosing ileopathy” and DIOS may coexist. SELECTION OF IMAGING PROCEDURE FOR SBO
In the acute setting where the diagnosis of highgrade or complete obstruction is suggested clinically and radiographically, CT with intravenous contrast is the most helpful imaging procedure. In
Fig 17. NSAID enteropathy. A 64-year-old woman with osteoarthritis on long term NSAID presented with intermittent colicky pain and anemia. Axial CTE shows multiple diaphragm-like strictures (arrows) of distal ileum.
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used if there is accompanying anemia or if active inflammatory disease is highly suspected, but the diagnosis of low-grade obstruction with demonstration of small fistulae or sinus tracts may be difficult to appreciate with this technique. CTE should be considered if conventional CT findings are equivocal in the acute setting or questions relevant to management are not fully answered. MANAGEMENT OF SBO: ROLE OF RADIOLOGIST
Fig 18. Cystic fibrosis related SBO. (A) Axial CT image of a 41-year-old woman with cystic fibrosis shows viscid secretions (arrows) and dilated proximal loops of small bowel. The appearance is consistent with distal intestinal obstruction syndrome (DIOS). (B) Axial CTE in a 42-year-old woman with cystic fibrosis shows distal SBO with focal stricture (arrow). Two other strictures were present in distal ileum (not shown). She had been on high-dose oral pancreatic enzyme supplements for several years. The appearances are probably because of mucosal inflammation caused by pancreatic supplements.
When the clinical setting is less well defined and where the possibility of low-grade SBO is considered, a CT or barium enteroclysis is more useful. Our preference is for CTE with positive enteral contrast for patients with symptoms of recurrent low-grade obstruction with a history of prior abdominal surgery or patients with higher grades of obstruction with complex abdominal history (multiple abdominal surgeries, Crohn’s disease, prior radiation treatment, possible extra-intestinal internal or external fistula).19 CTE, performed with intravenous contrast and infusion of neutral enteral contrast such as water or methylcellulose, can be
Despite over 100 years of experience in managing SBO, controversy exists as to the need and timing of surgery. In our institution, if obstruction is low-grade or within six weeks of a prior abdominal operation, a conservative approach with decompression of small bowel is tried. If there is partial high-grade obstruction, a trial of decompression is attempted since there will be a substantial rate of resolution.27,39,57,58 Prompt surgical intervention is usually indicated if there is complete SBO or if there are CT findings of CLO or strangulation. An adverse clinical picture, including tachycardia, leukocytosis, and fever also favors early surgery. A history of abdominal tumor, inflammatory bowel disease, or radiotherapy favors a conservative approach. The intestinal tract secretes up to 8.5 l of fluid every 24 hours. When bowel is obstructed, the fluid may not be reabsorbed depending on the site and chronicity of obstruction. Decompression of distended small bowel is important to reduce pain and the risk of venous impairment and ischemia. It is best achieved by placing a tube as close as possible to site of obstruction.16 A nasogastric tube does not allow for effective decompression unless the pyloric valve mechanism is overcome by the increased intraluminal pressure of high-grade obstruction. Thus, following initial gastric decompression, the tube should be advanced to the proximal small bowel for more effective decompression.16 Many surgeons, including those at our institution, prefer a nasointestinal tube for decompression. In centers where enteroclysis is performed to evaluate SBO, it may be advantageous to use a multipurpose tube (MDEC-1400, Cook, Bloomington, IN) for decompression and subsequent enteroclysis. This practice obviates the need for a second tube insertion, a procedure that is ranked as one of the most uncomfortable experienced by patients.16 The multipurpose tube is small (13.5 F), long (155 cm) (see Fig 12), and
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can be attached to suction devices. It is ideally placed in the emergency room (ER) or on the ward, where it is introduced into the stomach for gastric decompression. Subsequently, it can be advanced into the jejunum under fluoroscopy before performing CTE or EC. Nasointestinal decompression tubes are safe and no adverse event has been recorded over a long period of use. Following intestinal decompression or
enteroclysis, the tube should be withdrawn into the stomach if the obstruction is high-grade and reflux into the stomach is seen during the study. It is the radiologist’s responsibility to establish a protocol with ER physicians and surgeons for conservative management of patients with SBO. This may be particularly useful in patients with Crohn’s disease, prior surgery, or malignancy.
REFERENCES 1. Welch JP: General consideration and mortality in bowel obstruction, in Welch JP (ed): Bowel Obstruction: Differential Diagnosis and Clinical Management. Philadelphia, PA, Saunders, 1990, pp 59-95 2. Frager DH, Baer JW: Role of CT in evaluating patients with small-bowel obstruction. Semin Ultrasound CT MR 16: 127-140, 1995 3. Frager D, Medwid SW, Baer JW, et al: CT of small-bowel obstruction: Value in establishing the diagnosis and determining the degree and cause. AJR Am J Roentgenol 162:37-41, 1994 4. Maglinte DD, Reyes BL, Harmon BH, et al: Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR Am J Roentgenol 167:14511455, 1996 5. Markus JB, Somers S, Franic SE, et al: Interobserver variation in the interpretation of abdominal radiographs. Radiology 171:69-71, 1989 6. Mucha P Jr.: Small intestinal obstruction. Surg Clin North Am 67:597-620, 1987 7. Patel NH, Lauber PR: The meaning of a nonspecific abdominal gas pattern. Acad Radiol 2:667-669, 1995 8. Maglinte DDT: “Nonspecific abdominal gas pattern”: An interpretation whose time is gone. Emerg Radiol May/June:9395, 1996 9. Lappas JC, Reyes BL, Maglinte DD: Abdominal radiography findings in small-bowel obstruction: Relevance to triage for additional diagnostic imaging. AJR Am J Roentgenol 176: 167-174, 2001 10. Maglinte DD, Lappas JC, Heitkamp DE, et al: Technical refinements in enteroclysis. Radiol Clin North Am 41:213-229, 2003 11. Shrake PD, Rex DK, Lappas JC, et al: Radiographic evaluation of suspected small bowel obstruction. Am J Gastroenterol 86:175-178, 1991 12. Megibow AJ, Balthazar EJ, Cho KC, et al: Bowel obstruction: Evaluation with CT. Radiology 180:313-318, 1991 13. Fukuya T, Hawes DR, Lu CC, et al: CT diagnosis of small-bowel obstruction: Efficacy in 60 patients. AJR Am J Roentgenol 158:765-769, 1992 14. Gazelle GS, Goldberg MA, Wittenberg J, et al: Efficacy of CT in distinguishing small-bowel obstruction from other causes of small-bowel dilatation. AJR Am J Roentgenol 162: 43-47, 1994 15. Maglinte DD, Gage SN, Harmon BH, et al: Obstruction of the small intestine: Accuracy and role of CT in diagnosis. Radiology 188:61-64, 1993
16. Maglinte DD, Kelvin FM, Rowe MG, et al: Small-bowel obstruction: Optimizing radiologic investigation and nonsurgical management. Radiology 218:39-46, 2001 17. Mayo-Smith WW, Wittenberg J, Bennett GL, et al: The CT small bowel feces sign: Description and clinical significance. Clin Radiol 50:765-767, 1995 18. Donckier V, Closset J, Van Gansbeke D, et al: Contribution of computed tomography to decision making in the management of adhesive small bowel obstruction. Br J Surg 85:1071-1074, 1998 19. Maglinte DD, Bender GN, Heitkamp DE, et al: Multidetector-row helical CT enteroclysis. Radiol Clin North Am 41:249-262, 2003 20. Maglinte DD, Heitkamp DE, Howard TJ, et al: Current concepts in imaging of small bowel obstruction. Radiol Clin North Am 41:263-83, 2003 21. Bender GN, Timmons JH, Williard WC, et al: Computed tomographic enteroclysis: One methodology. Invest Radiol 31: 43-49, 1996 22. Bender GN, Maglinte DD, Kloppel VR, et al: CT enteroclysis: A superfluous diagnostic procedure or valuable when investigating small-bowel disease? AJR Am J Roentgenol 172: 373-378, 1999 23. Beall DP, Fortman BJ, Lawler BC, et al: Imaging bowel obstruction: A comparison between fast magnetic resonance imaging and helical computed tomography. Clin Radiol 57:719724, 2002 24. Davis SE, Sperling L: Obstruction of the small intestine. Arch Surg 99:424-426, 1969 25. Frazee RC, Mucha P Jr., Farnell MB, et al: Volvulus of the small intestine. Ann Surg 208:565-568, 1988 26. Otamiri T, Sjodahl R, Ihse I: Intestinal obstruction with strangulation of the small bowel. Acta Chir Scand 153:307-310, 1987 27. Sarr MG, Bulkley GB, Zuidema GD: Preoperative recognition of intestinal strangulation obstruction: Prospective evaluation of diagnostic capability. Am J Surg 145:176-182, 1983 28. Shatila AH, Chamberlain BE, Webb WR: Current status of diagnosis and management of strangulation obstruction of the small bowel. Am J Surg 132:299-303, 1976 29. Balthazar EJ, Bauman JS, Megibow AJ: CT diagnosis of closed loop obstruction. J Comput Assist Tomogr 9:953-955, 1985 30. Balthazar EJ, Birnbaum BA, Megibow AJ, et al: Closedloop and strangulating intestinal obstruction: CT signs. Radiology 185:769-775, 1992
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31. Ha HK, Park CH, Kim SK, et al: CT analysis of intestinal obstruction due to adhesions: Early detection of strangulation. J Comput Assist Tomogr 17:386-389, 1993 32. Ha HK: CT in the early detection of strangulation in intestinal obstruction. Semin Ultrasound CT MR 16:141-150, 1995 33. Ha HK, Kim JS, Lee MS, et al: Differentiation of simple and strangulated small-bowel obstructions: Usefulness of known CT criteria. Radiology 204:507-512, 1997 34. Barnett WO, Petro AB, Williamson JW: A current appraisal of problems with gangrenous bowel. Ann Surg 183:653659, 1976 35. Laws HL, Aldrete JS: Small-bowel obstruction: A review of 465 cases. South Med J 69:733-734, 1976 36. Zalcman M, Sy M, Donckier V, et al: Helical CT signs in the diagnosis of intestinal ischemia in small-bowel obstruction. AJR Am J Roentgenol 175:1601-1607, 2000 37. Balthazar EJ, Liebeskind ME, Macari M: Intestinal ischemia in patients in whom small bowel obstruction is suspected: Evaluation of accuracy, limitations, and clinical implications of CT in diagnosis. Radiology 205:519-522, 1997 38. Frager D, Baer JW, Medwid SW, et al: Detection of intestinal ischemia in patients with acute small-bowel obstruction due to adhesions or hernia: Efficacy of CT. AJR Am J Roentgenol 166:67-71, 1996 39. Taourel PG, Fabre JM, Pradel JA, et al: Value of CT in the diagnosis and management of patients with suspected acute small-bowel obstruction. AJR Am J Roentgenol 165:11871192, 1995 40. Horton KM, Fishman EK: The current status of multidetector row CT and three-dimensional imaging of the small bowel. Radiol Clin North Am 41:199-212, 2003 41. Frager DH, Baer JW, Rothpearl A, et al: Distinction between postoperative ileus and mechanical small-bowel obstruction: Value of CT compared with clinical and other radiographic findings. AJR Am J Roentgenol 164:891-894, 1995 42. Bizer LS, Liebling RW, Delany HM, et al: Small bowel obstruction: The role of nonoperative treatment in simple intestinal obstruction and predictive criteria for strangulation obstruction. Surgery 89:407-413, 1981 43. Menzies D, Ellis H: Intra-abdominal adhesions and their
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prevention by topical tissue plasminogen activator. J R Soc Med 82:534-535, 1989 44. Burkill G, Bell J, Healy J: Small bowel obstruction: The role of computed tomography in its diagnosis and management with reference to other imaging modalities. Eur Radiol 11:14051422, 2001 45. Ijiri R, Kanamaru H, Yokoyama H, et al: Obturator hernia: The usefulness of computed tomography in diagnosis. Surgery 119:137-140, 1996 46. Blachar A, Federle MP: Internal hernia: An increasingly common cause of small bowel obstruction. Semin Ultrasound CT MR 23:174-183, 2002 47. Miller PA, Mezwa DG, Feczko PJ, et al: Imaging of abdominal hernias. Radiographics 15:333-347, 1995 48. Maglinte DD, Gourtsoyiannis N, Rex D, et al: Classification of small bowel Crohn’s subtypes based on multimodality imaging. Radiol Clin North Am 41:285-303, 2003 49. Caroline DF, Herlinger H, Laufer I, et al: Small-bowel enema in the diagnosis of adhesive obstructions. AJR Am J Roentgenol 142:1133-1139, 1984 50. Reijnen HA, Joosten HJ, de Boer HH: Diagnosis and treatment of adult intussusception. Am J Surg 158:25-28, 1989 51. Delabrousse E, Bartholomot B, Sohm O, et al: Gallstone ileus: CT findings. Eur Radiol 10:938-940, 2000 52. Balthazar EJ, Schechter LS: Air in gallbladder: A frequent finding in gallstone ileus. AJR Am J Roentgenol 131: 219-222, 1978 53. Ko S, Lee T, Ng S: Small bowel obstruction due to phytobezoar: CT diagnosis. Abdom Imaging 22:471-473, 1997 54. Eggermont E: Gastrointestinal manifestations in cystic fibrosis. Eur J Gastroenterol Hepatol 8:731-738, 1996 55. Pawel BR, de Chadarevian JP, Franco ME: The pathology of fibrosing colonopathy of cystic fibrosis: A study of 12 cases and review of the literature. Hum Pathol 28:395-399, 1997 56. Lloyd-Still JD, Beno DW, Kimura RM: Cystic fibrosis colonopathy. Curr Gastroenterol Rep 1:231-237, 1999 57. Seror D, Feigin E, Szold A, et al: How conservatively can postoperative small bowel obstruction be treated? Am J Surg 165:121-125, 1993 58. Turner DM, Croom RD III: Acute adhesive obstruction of the small intestine. Am Surg 49:126-130, 1983
S
MALL BOWEL obstruction (SBO) is a common clinical condition, which accounts for about 12%-15% of acute abdominal admissions.1 History and physical findings are often suggestive of the diagnosis, which is straightforward when the classic picture of crampy abdominal pain, bilious vomiting, and abdominal distension is present. Plain abdominal radiographs in this setting often show multiple air fluid levels within dilated loops of small bowel, accompanied by a reduced amount of colonic gas. In many cases of confirmed SBO, however, the clinical picture is frequently vague. Plain radiography is often unhelpful, and the diagnosis may be in doubt. In these situations a routine abdomino-pelvic computed tomography (CT), fluoroscopic enteroclysis, or the combined study of CT and enteroclysis (CT enteroclysis) should be considered. Even when the diagnosis of SBO is unequivocal, further imaging may be required to identify the cause, site, and severity of the obstruction, and to determine whether bowel ischemia has developed. Specific radiological findings can often impact directly on the decision of whether a trial of nonoperative therapy can be safely undertaken or whether urgent surgical intervention is required. The radiologist may also aid clinical management by taking responsibility for the insertion of long naso-jejunal tubes to decompress the distended small bowel. In this article, we discuss the various imaging techniques to assess SBO, the features of complicated SBO, diagnostic clues to ascertain the etiology of SBO, and outline the role of the radiologist in the investigation and management of SBO. ABDOMINAL RADIOGRAPHY
The accuracy of abdominal radiography (AR) in diagnosing SBO is 50%-60%.2-6 In up to 10% of
cases, the information it supplies may be misleading.4 Improvement in the accuracy of AR begins with the consistent use of well-defined terminology. The term “nonspecific bowel gas pattern” is a time-honored descriptive phrase of variable meaning. It has been used to imply normality and abnormality, as well as uncertainty, as to the nature of any abnormality.5,7 The following terminology has been suggested to describe small bowel gas patterns to clarify imprecise or poorly understood terms in AR.8 1. Normal small bowel gas pattern: up to four loops of small bowel less than 2.5 cm in diameter and with normal distribution of gas and feces in nondistended colon. 2. Abnormal but nonspecific gas pattern: three or more air fluid levels in small bowel on horizontal beam films, with at least one loop distended to more than 3 cm, and colon either normal caliber or borderline distended. This appearance may represent either low-grade SBO or adynamic ileus and may require further evaluation by barium enteroclysis or CT enteroclysis (Fig 1). 3. Probable SBO pattern: multiple gas- and fluidfilled loops of distended small bowel with a moderate amount of colonic gas. It may be seen
From the Departments of Radiology and Surgery, Indiana University School of Medicine, Indianapolis, IN; Department of Radiology, Methodist Hospital of Indiana, Indianapolis, IN. Address reprint requests to Dean D. T. Maglinte, M.D., Department of Radiology, Indiana University Medical Center, 550 N University Boulevard, University Hospital, Indianapolis, IN 46202-5257. © 2003 Elsevier Inc. All rights reserved. 0887-2171/03/2905-0000$30.00/0 doi:10.1053/sult.2003.0000
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Fig 2. Probable SBO pattern. (A) Supine abdominal radiograph of an elderly female with recurrent abdominal pain, prior pelvic surgery, and external radiation for endometrial carcinoma shows moderately distended gas and fluid-filled loops of small bowel (arrows) and some gas in segments of colon. (B) Axial CTE image shows stricture (straight arrow) and dense mesenteric adhesions (arrow heads) fixing loops of small bowel with dilatation of proximal loops.
Fig 1. Abnormal but nonspecific gas pattern. (A) Upright abdominal radiograph of a middle-aged patient with recurrent abdominal pain and prior appendectomy shows multiple mildly dilated pelvic loops of ileum with air fluid levels (arrow) and normal gas distribution in colon. (B) Radiograph obtained during single contrast phase of enteroclysis shows dilated loop of small bowel in pelvis with abrupt cutoff (arrow). Further infusion showed contrast in normal distal ileum (not shown). Surgery confirmed dense adhesive band obstruction.
in early complete SBO, partial high-grade SBO, or adynamic ileus. These patients should ideally have a CT examination and if this is inconclusive a CT enteroclysis should be entertained, especially in patients with multiple prior abdominal surgeries or radiation (Fig 2). 4. Definite SBO: Dilated fluid-filled loops of small bowel with a gasless colon. This is diagnostic for SBO, and in our institution an emergent CT is usually obtained to assess for strangulation. In the absence of strangulation, following partial decompression, barium enteroclysis or CT enteroclysis can be done if further characterization of the severity or
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etiology of obstruction is clinically warranted (Fig 3). A study assessing 81 patients9 with varying degrees of SBO showed that the presence of differential air-fluid levels in the same loop of bowel and a mean air fluid level of more than 25 mm on erect AR strongly suggests high-grade rather than low-grade obstruction. In this study, the classic string of beads sign did not reliably differentiate between high- and low-grade obstructions. Despite some accuracy in making the diagnosis of SBO, AR is notoriously poor at determining the site and etiology of SBO (Fig 4). BARIUM RADIOGRAPHY
Barium does not inspissate in an adynamic gut and, therefore, can be administered orally to evaluate SBO. Because orally ingested iodinated water soluble contrast agents are hypertonic and have poor mucosal coating, they are best not employed for the oral evaluation of SBO.10 Barium examination without intubation is used in centers where expertise for enteroclysis (EC) is not available. These oral small bowel follow-through studies are time consuming, and often fail to accurately demonstrate the site of obstruction. Further, retention of barium above a high-grade obstruction often delays subsequent performance of CT. EC, on the other hand, is a minimally invasive procedure and is best performed with conscious sedation of the patient. Barium EC can correctly predict the presence, level, and cause of obstruction with an accuracy of 86%-100%.11 By EC criteria, the upper limits of caliber for jejunum and ileum are 3 cm and 2.5 cm, respectively. The diagnosis of SBO is made by identifying a transition zone characterized by a distinct change in caliber. The degree of SBO is graded based on objective criteria proposed by the Indiana group as follows:11 1. Low-grade partial 2. High-grade partial 3. Complete In low-grade partial SBO, there is little or no delay in arrival of contrast to the transition zone, and there is sufficient passage of contrast material to delineate the mucosal pattern of post-obstructive bowel. In high-grade partial obstruction, only a small amount of dilute contrast material is seen to traverse the transition zone. EC is usually not necessary in suspected complete SBO unless the
Fig 3. Definite SBO pattern. (A) Upright abdominal radiograph of an elderly patient with prior pelvic surgery shows air fluid levels in moderately distended small bowel loops (arrows) and feces in nondistended colon. (B) Following overnight long tube decompression, barium enteroclysis shows dense adhesive band obstruction (arrow) in a loop of ileum in upper pelvis.
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CT are its ability to distinguish low-grade SBO from normalcy, and to assess patients who may be harboring more than one site of obstruction. It is possible to combine some of the advantages of both techniques with the hybrid technique of CT enteroclysis. In our institution, it is usual to perform CT enteroclysis using water-soluble contrast instead of fluoroscopic barium enteroclysis in situations of incomplete SBO, unless it is considered important to also demonstrate mucosal detail, as may be the case in Crohn’s disease. CT CT has become an important tool in the preoperative assessment of patients with SBO. Early studies focused predominantly on patients with high-grade obstruction. These reports found a sensitivity of 78%-96% and accuracy of about 90%95%.12-14 Later studies, which included lower grades of SBO, reported an overall sensitivity and accuracy of 63%-66%.15 This lower accuracy is because of the poor sensitivity of CT in evaluating patients with low-grade SBO (48%-50%).2,15,16 However, it remains accurate for high-grade partial and complete SBO. CT Technique
Fig 4. Unreliability of abdominal radiography in determining the site of obstruction. (A) Supine abdominal radiography of an elderly patient with nausea and vomiting shows disproportionately dilated loop of jejunum (arrow) and a few mildly distended loops more distally. (B) Radiographs obtained during single contrast phase of a barium enteroclysis shows dense adhesive band obstruction (arrow) in a loop of distal ileum in right upper pelvis.
patient has a history of complex abdominal surgery. If performed, there will be no passage of contrast beyond the obstruction on delayed radiographs. The main advantages of EC over routine
There is no consensus as to whether oral contrast material is necessary. Arguments against the use of positive oral contrast material have focused on the risk of vomiting, delay in diagnosis, and lack of progression of the orally ingested material because of the obstruction. Furthermore, the reduction of contrast between intestinal lumen and wall makes measurement of the thickness of the small bowel wall more difficult. In the era of multichannel CT, dense oral contrast material may interfere with image reconstruction. We do not usually use positive oral contrast material when high-grade SBO is suspected, but it may be useful in appreciating mesenteric fluid collections and may show the transition zone better in low-grade obstructions. The positive contrast material may be either a 1.2% solution of barium or a 2% solution of iodinated water-soluble contrast. It is routine practice to give intravenous contrast in patients with SBO unless there are contraindications to its use. With multichannel CT scanners, a slice width between 5 mm and 7 mm is used, with approximately 50% overlap reconstruction. If necessary, the raw data can be reconstructed at thinner slices at the suspected
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transition zone. Our experience is that the diagnostic confidence is improved if soft copy images are reviewed on a workstation using cine scrolling. This technique includes the ability to perform instantaneous multiplanar reconstructions (MPR). We find that MPR is particularly useful in finding the transition zone of SBO or identifying internal hernia and closed loop obstruction. CT Diagnosis To diagnose SBO, a transition zone between dilated small bowel (⬎2.5 cm) and normal caliber small bowel must be seen (Fig 5). Diffusely dilated small bowel or air fluid levels are not reliable in distinguishing adynamic ileus from mechanical SBO. The presence of fecal matter in small bowel, the small bowel feces sign, is abnormal. This finding is usually seen in patients with chronic SBO. Uncommon causes of this sign in the absence of SBO include infectious enteritis and over-vigorous jejunal tube feeding.17 The site of obstruction has therapeutic implications. Proximal SBO is more likely to resolve nonoperatively than distal ones.18 CT has been found to be about 94% accurate in assessing whether or not a SBO is proximal in location.3 Difficulties arise if bowel loops are not meticulously followed since jejunum may lie in the pelvis and ileal loops may lie in the upper abdomen, especially if there is prior surgery. The classification of low-grade, high-grade partial, and complete SBO is used, although this determination is harder to make with conventional CT compared to enteroclysis. CT Enteroclysis CT enteroclysis (CTE) has been promoted because it is a hybrid procedure that combines the advantages of CT and EC into a single test. The former allows 3D acquisition and global assessment of bowel wall and mesentery, whereas the latter allows better recognition of mucosal detail and the diagnosis of low-grade SBO. CTE does have its disadvantages, the foremost of which is the need for placement of a nasoenteric tube. If CTE is performed with neutral oral contrast, such as water, intravenous contrast may be given. The procedure of CTE is described elsewhere.19 Our group analyzed 92 patients with documented SBO who had both CT and CTE during the diagnostic work-up; sensi-
Fig 5. Conventional abdominopelvic CT in SBO. (A) Axial image at the level of the kidneys shows abrupt transition in the caliber of small bowel loops and collapsed or normal caliber small bowel loops indicating transition zone (arrow). Assessment of bowel wall perfusion is possible with intravenous contrast and a neutral oral contrast such as water. (B) Barium enteroclysis performed the following day confirms transition zone in right hemi-abdomen anteriorly (arrow), proven to be a dense adhesive band at surgery. Note collapsed loops distal to transition point.
tivity rates of 60% for conventional CT and 98% for CTE were recorded.20 Of the 19 false-negative cases recorded by conventional CT, 17 were found to be low-grade SBO on CTE (Fig 6).
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Fig 6. CTE. Why bother? (A) Axial image of conventional CT at level of upper pelvis of an elderly woman with symptoms of SBO and prior hysterectomy shows multiple diverticula in sigmoid. Small bowel loops are of normal caliber. (B) Axial image at level of lower pelvis shows normal appearance of posterior vaginal cuff (arrow). (C) CTE, performed because of persistent symptoms, shows mildly dilated loops of ileum because of anterior peritoneal adhesions (arrows) and nondistended distal ileum indicating low-grade SBO. In addition, a sinus tract is opacified, leading to a small fluid collection (arrowhead) consistent with a small diverticular abscess. (D) Image at level of lower pelvis shows fistulous communication with the posterior vaginal cuff, indicated by presence of infused enteral contrast (arrow).
Barium enteroclysis is known to be of value in diagnosing lower grades of SBO but does not give information on extra-intestinal manifestations of disease. Traditionally, barium enteroclysis and CTE have been shown to be of similar accuracy in low-grade SBO.21 It is not clear if CTE using a
multichannel CT scanner is superior since it allows for thinner slice width. In addition, many surgeons are reluctant to allow use of barium in patients who may be surgical candidates. CTE is less operatordependent and provides uniform results over a wide spectrum of patients.22
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Table 1. Advantages and Disadvantages of Sequences Used in MRI Enteroclysis Sequence
HASTE
Advantage(s)
1. 2. 3. 1. 2.
true FISP
T2 w TSE
T1 w post gadolinium series with fat saturation
Disadvantage(s)
Reduced susceptibility artifact No black boundary artifact High lumen to wall contrast Insensitive to motion artifacts High contrast between lumen and wall
1. Good soft tissue contrast-lesion characterization 2. Reduced black boundary and susceptibility artifact 1. Assessment of vascularity of bowel wall 2. Good contrast resolution
MRI AND MR ENTEROCLYSIS
MRI has not been extensively used to assess bowel disorders. With increasingly fast sequences, many now completed within a single breath-hold, it is now possible to image the entire abdomen and pelvis within 10 minutes. Typical sequences used are half-Fourier single shot turbo spin-echo (HASTE), true fast imaging with steady state precession (true FISP), and gadolinium-enhanced fat saturated T1-weighted volume acquisition (VIBE, 3D FLASH, or FAME). Each sequence has its advantages and disadvantages (Table 1). A recent study based on 25 patients reported that HASTE imaging in 3 planes was superior to helical CT in diagnosing SBO,23 however, there was no mention of the severity of the SBO. These findings remain to be confirmed by other authors. Currently, MR methods of examination are not part of the routine evaluation of SBO. COMPLICATED OBSTRUCTION
An important question to be answered during the imaging of SBO is whether the obstruction has been complicated by the development of ischemia. The radiologist, therefore, needs to be familiar with the CT features of closed loop obstruction and strangulation. Closed Loop Obstruction Closed loop obstruction (CLO) occurs when a variable length of small bowel is obstructed at both ends leaving a segment that is unable to be decompressed. This situation is seen in approximately 10% of SBO. The mortality of this complication
1. Sensitive to flow artifact (reduced by intravenous glucagon) 2. Poor visualization of mesentery 1. Black boundary artifact, cannot determine wall thickness (reduced with fat suppression) 2. Sensitivity to susceptibility artifact 1. Susceptible to motion artifact
1. Reduced spatial resolution 2. Fat containing stool may mimic enhancing lesion (overcome by subtracting post- from pregadolinium series)
can be as high as 35% and rises sharply if diagnosis is delayed by more than 36 hours. The importance of CLO lies in the high incidence of associated strangulation, as the obstructed loop is free to rotate along its axis. Importantly, clinical signs are often inconclusive. Studies in which CT was not used as an integral part of the diagnostic pathway preoperatively diagnosed CLO in only 50%-80% cases.24-28 CLO is usually caused by adhesions or hernias. CT signs of CLO depend upon the 3D orientation of the obstructed loop and have been well described by Balthazar:29,30 1. If the loop is horizontal, CT shows a distended fluid-filled C or U shaped loop with engorged mesenteric vessels. The two ends of the distended loop come together. 2. If the bowel is more vertically orientated, the diagnosis is slightly more difficult. Recognition depends on appreciating fluid-filled loops radiating away from the sites of obstruction. Coronal and sagittal reconstructions help increase diagnostic certainty. 3. At the site of obstruction, the collapsed loops may be oval or triangular. 4. A beak sign may be seen, caused by the gradual tapering of the afferent and efferent limbs near the point of obstruction. 5. The proximal bowel is likely to be distended, to a lesser degree than the closed loop that is typically filled only with fluid. The distal bowel is nondistended. The sensitivity of CT diagnosis for CLO is about 85%.30 Barium enteroclysis has been shown to
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Fig 7. Multichannel CT enteroclysis of closed loop obstruction. (A) Radiographic phase of a CTE with positive enteral contrast in a patient with renal transplant and prior surgery for SBO shows the tip of the enteroclysis catheter in the distal duodenum. The proximal jejunum is dilated secondary to a linear defect (arrow). The loop of jejunum distal to the linear defect is also dilated (arrowhead). The radiograph was obtained in the right posterior oblique position. (B) Coronal and (C) axial image at level of balloon shows the distended limbs of the involved segment (arrowheads). (D) Axial image at a lower level shows the dense mesenteric adhesive band (arrow) producing the closed loop obstruction. Contrast is seen in the dilated duodenum. (D) Closed loop obstruction from adhesions without evidence of strangulation was confirmed at surgery.
demonstrate closed loop configuration in lowgrade obstruction. In our recent experience, multichannel CTE simplifies the demonstration of closed loop configuration of SBO (Fig 7). Strangulating Obstruction The various manifestations of strangulation have been recently reviewed by Ha.31-33 Strangulation
can occur in closed loop obstruction or, less commonly, in simple obstruction where the pressure of luminal distension causes impairment of venous drainage. Volvulus because of congenital malrotation or primary small bowel volvulus, as seen in African patients, is a rare cause of strangulation. CLO does not equate to strangulation and merely signifies incarceration, which may be reversible.
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Strangulation is found in about 10%-15% of patients undergoing surgery for SBO,27,30 and is associated with a mortality of 20%-30%.27,28,34,35 The diagnosis is usually not made on clinical grounds. Before routine use of CT, up to 85% of patients with the surgical finding of strangulated small bowel were not correctly diagnosed preoperatively.30 The recognized CT findings30,32,36 in early strangulation include wall thickening, target or halo appearance because of submucosal edema, mesenteric vessel engorgement, and ascites. More advanced ischemia is heralded by mesenteric vessel blurring, hemorrhagic ascites, enhancement of thickened wall on delayed images, pneumatosis, and mesenteric or portal venous gas (Fig 8). In earlier studies, the sensitivity of CT in detecting ischemia was reported between 60%80%.30,37-39 A study with faster helical CT scanning has shown a higher accuracy of 95%,36 likely related to the better contrast bolus achievable with such scanners. It is possible to detect reduced early enhancement of bowel wall as a highly specific sign for ischemia. With current multichannel CT it is probable that diagnostic confidence of assessing bowel vascularity will be even better.40 To our knowledge, no large studies have been published using dual or triple phase examinations of small bowel to detect abnormal enhancement patterns. Differential diagnosis of small bowel wall edema and mesenteric inflammatory changes include bowel hemorrhage or focal inflammation. The findings of impaired vascular enhancement and bowel obstruction make strangulation the more likely cause of this appearance. SBO vs. Adynamic Ileus In ileus, there is usually distension of both small and large bowel. However, in generalized ileus, the colonic distension usually predominates. In some patients, particularly in those with peritonitis, there is variable distension of the proximal colon with a nondistended left colon. This should not be mistaken for mechanical obstruction in the proximal colon (Fig 9). The best CT sign of SBO is the presence of an identifiable transition zone in the small bowel. Early studies have suggested CT is 100% accurate in differentiating the two conditions.41 However, these authors reflected that this may represent an unduly high figure,2 an opinion with which we concur. If CT findings are equivocal, CTE often yields the correct diagnosis.
Fig 8. Strangulating obstruction. (A) Axial CT image of mid-abdomen in 76-year-old patient with strangulating obstruction shows gas within linear mesenteric structures consistent with mesenteric venous gas (arrow). Gas is seen adjacent to intravenous contrast opacified vascular lumen. (B) Axial CT at a lower level shows air in dependent wall of small bowel loop (pneumatosis) (arrows) and free peritoneal air (arrowheads).
ETIOLOGY OF SBO
The three most common causes of SBO in the western world are (1) adhesions, (2) Crohn’s disease, and (3) neoplasm.20 Hernia used to be an important etiology of SBO, but early detection and
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tory of abdominal surgery.44 The diagnosis of adhesions is presumed on CT if there is a narrow zone of transition without an identifiable obstructive lesion. The characteristics and location of adhesions are easily demonstrated by CTE (Fig 10). In our experience, CTE with positive enteral contrast is the best method of characterizing adhesions, particularly in patients with recurrent lowgrade partial SBO. External Hernia Indirect inguinal hernia is the commonest hernia. It is clinically obvious, but CT may be helpful in obese patients or those with inguinal scars. Femoral hernias may be notoriously difficult to identify clinically but are fairly obvious on a good quality CT. CT is also useful for other external hernia, such as obturator hernia, which are difficult to diagnose and have a mortality as high as 25%.45 Internal Hernia
Fig 9. Difficulty in differentiating SBO and adynamic ileus. (A) Axial CT image of mid-abdomen in a patient with renal failure and peritonitis shows distention of small bowel but right colon is collapsed (arrows). The appearances suggest mechanical distal SBO. However, no clear transition zone is seen. Ascites is present. (B) A second CT scan two days later shows right colon is now of normal caliber (arrow) indicating the bowel changes were ileus secondary to peritonitis.
In internal hernia, unlike the external variety, the bowel herniates through the peritoneal covering and lies trapped within the abdominal cavity. The risk of strangulation or obstruction is substantial. The locations of these types of internal hernia include left and right paraduodenal, foramen of Winslow, transmesenteric, transomental, and paracecal. A complete discussion of CT features of internal hernia is beyond the scope of this article, and the interested reader is referred to specific
more aggressive elective repair has led to a considerable decline in the prevalence of hernia-induced SBO. In developing countries, hernia remains an important cause of SBO. The CT findings of different causes of SBO are discussed below. Adhesions Adhesions cause about 50%-75% of SBOs.42 They arise from prior surgery in most cases. Ninety percent of patients undergoing abdominal surgery have been found to have adhesions on subsequent laparotomy; most of these are not obstructing.43 Adhesions may also be congenital or occur following abdominal inflammation such as pelvic inflammatory disease or endometriosis. Thus, 10% of adhesions are found in patients without prior his-
Fig 10. SBO because of adhesions in a patient with abdominal malignancy. Dense adhesive band obstruction in a patient with known metastatic liver disease from carcinoid (not shown) suspected of having abdominal carcinomatoses. A smooth transition point in the anterior abdomen (arrow) is seen consistent with adhesive band obstruction. (Reproduced with permission from Maglinte, et al.)
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Crohn’s Disease
Fig 11. Left paraduodenal hernia. Axial CT of a 48-year-old woman shows small bowel loops (white arrow) between stomach (S) and pancreas (P), lying behind a branch of inferior mesenteric artery (black arrow). Patient presented with recurrent abdominal pain. An incarcerated left paraduodenal hernia was confirmed at surgery.
texts.46,47 The commonest type of internal hernia is a left paraduodenal hernia. However, with the increasing incidence of complex abdominal surgery, such as Roux-en-Y gastric bypass, transomental hernia is becoming more widespread. In left paraduodenal hernia there is herniation of the 4th part of the duodenum and proximal jejunum through a defect in the posterior peritoneum and the confluence of small bowel mesentery, transverse, and descending mesocolon. Half are present with acute or subacute obstruction. The classic finding is of dilated loops of jejunum in a rounded configuration between the inferior mesenteric vein, which forms an antero-superior border of the neck of the hernia, and the ascending left colic vein that forms the inferior border. There may be pressure effect on the posterior stomach (Fig 11). In obstructed transmesenteric hernia, there is dilated small bowel anterior to the transverse colon without discernible omentum between small bowel and abdominal wall. Detection of internal hernia is not easy on CT. The key to diagnosis is identification of the abnormal position of the small bowel and the altered course of mesenteric vessels. However, unusual positions of small bowel and its mesentery may be encountered in asymptomatic postoperative patients because of incision of their peritoneal attachments.
The CT signs of active Crohn’s disease are well established.48 Signs of acute inflammation include the target appearance of bowel with enhancing mucosa and serosa, and edematous submucosa and the “comb” sign because of perienteric hyperemia. In the chronic situation, fibrofatty proliferation can be seen. Immune modulating drugs such as infliximab (Remicaid) have become important in reducing disease activity and treating fistulae. However, they may worsen pre-existing small bowel strictures leading to frank intestinal obstruction. In our experience, we find CTE performed with intravenous contrast and water or methylcellulose as neutral enteral contrast to be the most reliable technique for detecting inflammatory changes, and CTE with positive enteral contrast the optimal method in demonstrating stenosis and fistula (Fig 12). For a treatise on current concepts in imaging of Crohn’s disease, the reader is referred to a recent review article.48 Patients Treated with Cancer The cause of SBO in up to 40% of patients with known intra-abdominal malignancy is adhesions.6 Hernias, radiation enteritis, and neoplastic compression account for the remainder. EC is 88% accurate for differentiating adhesions from other causes of partial SBO in patients with known malignancy.49 CTE has been reported to be an excellent technique for assessing these patients (Fig 13).21 Intussusception Intussusception accounts for 5% of SBO in adults.50 CT appearances of small bowel intussusceptions vary, depending partly on the severity of the intussusception. A dilated loop of bowel containing an eccentric crescent of fat, representing the mesentery of the intussusceptum, is an early finding. There may be mild proximal obstruction. More advanced stages are depicted by a sausageshaped mass with alternating layers of low (mesenteric fat) and high attenuation (bowel wall). Obstruction will be evident by this stage. If diagnosis is delayed, a reniform mass may be seen with peripheral high attenuation of bowel wall and variable attenuation of the center of the mass because of ischemia, oral contrast, and bowel gas. The invaginated mesenteric fat may not be visible because of edema and necrosis (Fig 14).
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Fig 12. CTE in Crohn’s disease. (A) Abdominal radiograph of a 79-year-old patient with known Crohn’s disease shows massive distention of multiple loops of small bowel. (B) Supine abdominal radiograph following overnight gastric decompression with long tube shows decreased distention of small bowel loops. (C) Axial CTE image of lower abdomen following infusion of positive enteral contrast shows markedly distended small bowel proximal to a long segment of stenosis in distal ileum (arrow); C ⴝ cecum. (D) Axial image of upper pelvis shows a small fistula (arrow) between stenosed segment and sigmoid colon (S). (Reproduced with permission from Maglinte, et al.)
Obturation Obstruction Gall stone ileus is a rare condition seen predominantly in elderly females. It has a mortality of up to 27%.51 The classic plain radiographic constellation (Rigler’s triad) of SBO, pneumobilia, and ectopic gallstone is seen in only a third of cases.52
CT findings are similar, but the obstructing gallstone is more easily identified (Fig 15). Phytobezoar are impacted luminal masses containing indigestible food. They are more likely to occur in patients following gastrectomy or with autonomic neuropathy. The commonest site of ob-
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Drug Induced Enteropathy Nonsteroidal anti-inflammatory drug (NSAID) induced enteropathy is an uncommon cause of small bowel strictures. Typically, on barium radiography or CTE, multiple constricting diaphragms are seen (Fig 17). Patients usually have a history of taking NSAIDs for more than six months. The enteropathy can occur with rectal as well as oral preparations. The mechanism of small bowel mucosal damage is not clear. The findings on enteroclysis are well described but can be difficult to make if the radiologist is not aware of the clinical picture. Cystic Fibrosis Related SBO Fibrosing colopathy (FC) is a recently recognized complication in children and adults with cystic fibrosis (CF) and other patients taking pancreatic enzyme supplements.54-56 There is edema of the distal bowel wall leading to focal strictures (Fig 18). This has been described in the right colon in patients taking some, but not all, forms of pancreatic enzyme supplements. There is suspicion, not proven, that it may be related to the dose of enzyme, though other factors such as enteric coating may also be responsible. We are aware of the presence of multifocal intermediate length (approximately 5 cm) strictures of ileum in older
Fig 13. Value of CTE for assessing SBO in patients with malignancy. (A) Axial CTE image of an elderly patient with prior surgery for sigmoid malignancy. Partial obstruction secondary to serosal metastases (white arrow) is shown. Ascitic fluid and distended small bowel loops (black arrows) are present. Also note anterior peritoneal implants (curved arrow). (Reproduced with permission from Maglinte, et al.) (B) A 72-year-old man with sigmoid cancer treated with surgery and high-dose external beam radiotherapy. Nine months later he presents with constipation. CEA is normal. Proximal bowel loops are distended. There is wall thickening and stricture of a pelvic loop of ileum (arrow) consistent with radiation enteritis. No mass is seen. Also note radiation injury to sigmoid colon (curved arrow).
struction by a phytobezoar is the jejunum or proximal ileum.53 These masses have a fairly classic appearance on CT. Differentiation from small bowel feces, found in chronic SBO, may be difficult. Encapsulation, rounded configuration of mass, wall thickening, and mesenteric edema at the site of the mass are more likely to be associated with phytobezoar (Fig 16).
Fig 14. Intussusception. Axial CT image of 47-year-old male with acute abdominal pain shows a long segment of intussusception. The proximal limb shows bowel within bowel appearance (curved arrows). The mesentery of intussusceptum is edematous and has higher density (white arrows). The intussusception has a reniform appearance. The wall shows mixed density because of presence of oral contrast, edema, and hemorrhage (arrowheads). Hemorrhagic ascites (black arrow) is present. At surgery, 120 cm of small bowel with necrosis was removed. Surgical pathology did not show a lead point.
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Fig 16. Afferent loop obstruction with phytobezoar. A 29year-old morbidly obese patient underwent gastric Roux-en-Y gastric bypass 5 months previously. She presented with abdominal pain. The afferent loop ends blindly and should have been less than 10 cm long. However, a long afferent loop was fashioned in this patient, and the loop became obstructed with ingested plant material (arrows). The phytobezoar can simulate feces (see text).
Fig 15. CT “Rigler’s triad” of gallstone ileus. (A) Axial CT image of upper abdomen in elderly female patient with abdominal pain and vomiting shows small gallstone (black arrow) in gall bladder. Air in gall bladder and common duct (white arrows) is present. Note distended stomach (S). (B) A 2-cm laminated gallstone (black arrow) in ileum with dilation of proximal segment. Distal ileum is collapsed (white arrow).
addition to detecting the severity, location, and probable etiology of SBO, it is also useful in determining the presence of bowel ischemia or other explanation for the symptoms such as diverticulitis and appendicitis.
patients with cystic fibrosis. This “fibrosing ileopathy” may mimic Crohn’s disease but, histologically, granuloma are not seen. In our limited experience of this condition, we find that CTE has been superior to other methods of diagnosis. Water-soluble contrast media used for enteral infusion aids in the evacuation of inspissated secretions in the small bowel and colon. Other causes of SBO in CF patients include intussusception and distal intestinal obstruction syndrome (DIOS). The latter is similar to meconium ileus equivalent in children and is because of the presence of inspissated secretions (Fig 18). It is quite possible that “fibrosing ileopathy” and DIOS may coexist. SELECTION OF IMAGING PROCEDURE FOR SBO
In the acute setting where the diagnosis of highgrade or complete obstruction is suggested clinically and radiographically, CT with intravenous contrast is the most helpful imaging procedure. In
Fig 17. NSAID enteropathy. A 64-year-old woman with osteoarthritis on long term NSAID presented with intermittent colicky pain and anemia. Axial CTE shows multiple diaphragm-like strictures (arrows) of distal ileum.
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used if there is accompanying anemia or if active inflammatory disease is highly suspected, but the diagnosis of low-grade obstruction with demonstration of small fistulae or sinus tracts may be difficult to appreciate with this technique. CTE should be considered if conventional CT findings are equivocal in the acute setting or questions relevant to management are not fully answered. MANAGEMENT OF SBO: ROLE OF RADIOLOGIST
Fig 18. Cystic fibrosis related SBO. (A) Axial CT image of a 41-year-old woman with cystic fibrosis shows viscid secretions (arrows) and dilated proximal loops of small bowel. The appearance is consistent with distal intestinal obstruction syndrome (DIOS). (B) Axial CTE in a 42-year-old woman with cystic fibrosis shows distal SBO with focal stricture (arrow). Two other strictures were present in distal ileum (not shown). She had been on high-dose oral pancreatic enzyme supplements for several years. The appearances are probably because of mucosal inflammation caused by pancreatic supplements.
When the clinical setting is less well defined and where the possibility of low-grade SBO is considered, a CT or barium enteroclysis is more useful. Our preference is for CTE with positive enteral contrast for patients with symptoms of recurrent low-grade obstruction with a history of prior abdominal surgery or patients with higher grades of obstruction with complex abdominal history (multiple abdominal surgeries, Crohn’s disease, prior radiation treatment, possible extra-intestinal internal or external fistula).19 CTE, performed with intravenous contrast and infusion of neutral enteral contrast such as water or methylcellulose, can be
Despite over 100 years of experience in managing SBO, controversy exists as to the need and timing of surgery. In our institution, if obstruction is low-grade or within six weeks of a prior abdominal operation, a conservative approach with decompression of small bowel is tried. If there is partial high-grade obstruction, a trial of decompression is attempted since there will be a substantial rate of resolution.27,39,57,58 Prompt surgical intervention is usually indicated if there is complete SBO or if there are CT findings of CLO or strangulation. An adverse clinical picture, including tachycardia, leukocytosis, and fever also favors early surgery. A history of abdominal tumor, inflammatory bowel disease, or radiotherapy favors a conservative approach. The intestinal tract secretes up to 8.5 l of fluid every 24 hours. When bowel is obstructed, the fluid may not be reabsorbed depending on the site and chronicity of obstruction. Decompression of distended small bowel is important to reduce pain and the risk of venous impairment and ischemia. It is best achieved by placing a tube as close as possible to site of obstruction.16 A nasogastric tube does not allow for effective decompression unless the pyloric valve mechanism is overcome by the increased intraluminal pressure of high-grade obstruction. Thus, following initial gastric decompression, the tube should be advanced to the proximal small bowel for more effective decompression.16 Many surgeons, including those at our institution, prefer a nasointestinal tube for decompression. In centers where enteroclysis is performed to evaluate SBO, it may be advantageous to use a multipurpose tube (MDEC-1400, Cook, Bloomington, IN) for decompression and subsequent enteroclysis. This practice obviates the need for a second tube insertion, a procedure that is ranked as one of the most uncomfortable experienced by patients.16 The multipurpose tube is small (13.5 F), long (155 cm) (see Fig 12), and
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can be attached to suction devices. It is ideally placed in the emergency room (ER) or on the ward, where it is introduced into the stomach for gastric decompression. Subsequently, it can be advanced into the jejunum under fluoroscopy before performing CTE or EC. Nasointestinal decompression tubes are safe and no adverse event has been recorded over a long period of use. Following intestinal decompression or
enteroclysis, the tube should be withdrawn into the stomach if the obstruction is high-grade and reflux into the stomach is seen during the study. It is the radiologist’s responsibility to establish a protocol with ER physicians and surgeons for conservative management of patients with SBO. This may be particularly useful in patients with Crohn’s disease, prior surgery, or malignancy.
REFERENCES 1. Welch JP: General consideration and mortality in bowel obstruction, in Welch JP (ed): Bowel Obstruction: Differential Diagnosis and Clinical Management. Philadelphia, PA, Saunders, 1990, pp 59-95 2. Frager DH, Baer JW: Role of CT in evaluating patients with small-bowel obstruction. Semin Ultrasound CT MR 16: 127-140, 1995 3. Frager D, Medwid SW, Baer JW, et al: CT of small-bowel obstruction: Value in establishing the diagnosis and determining the degree and cause. AJR Am J Roentgenol 162:37-41, 1994 4. Maglinte DD, Reyes BL, Harmon BH, et al: Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR Am J Roentgenol 167:14511455, 1996 5. Markus JB, Somers S, Franic SE, et al: Interobserver variation in the interpretation of abdominal radiographs. Radiology 171:69-71, 1989 6. Mucha P Jr.: Small intestinal obstruction. Surg Clin North Am 67:597-620, 1987 7. Patel NH, Lauber PR: The meaning of a nonspecific abdominal gas pattern. Acad Radiol 2:667-669, 1995 8. Maglinte DDT: “Nonspecific abdominal gas pattern”: An interpretation whose time is gone. Emerg Radiol May/June:9395, 1996 9. Lappas JC, Reyes BL, Maglinte DD: Abdominal radiography findings in small-bowel obstruction: Relevance to triage for additional diagnostic imaging. AJR Am J Roentgenol 176: 167-174, 2001 10. Maglinte DD, Lappas JC, Heitkamp DE, et al: Technical refinements in enteroclysis. Radiol Clin North Am 41:213-229, 2003 11. Shrake PD, Rex DK, Lappas JC, et al: Radiographic evaluation of suspected small bowel obstruction. Am J Gastroenterol 86:175-178, 1991 12. Megibow AJ, Balthazar EJ, Cho KC, et al: Bowel obstruction: Evaluation with CT. Radiology 180:313-318, 1991 13. Fukuya T, Hawes DR, Lu CC, et al: CT diagnosis of small-bowel obstruction: Efficacy in 60 patients. AJR Am J Roentgenol 158:765-769, 1992 14. Gazelle GS, Goldberg MA, Wittenberg J, et al: Efficacy of CT in distinguishing small-bowel obstruction from other causes of small-bowel dilatation. AJR Am J Roentgenol 162: 43-47, 1994 15. Maglinte DD, Gage SN, Harmon BH, et al: Obstruction of the small intestine: Accuracy and role of CT in diagnosis. Radiology 188:61-64, 1993
16. Maglinte DD, Kelvin FM, Rowe MG, et al: Small-bowel obstruction: Optimizing radiologic investigation and nonsurgical management. Radiology 218:39-46, 2001 17. Mayo-Smith WW, Wittenberg J, Bennett GL, et al: The CT small bowel feces sign: Description and clinical significance. Clin Radiol 50:765-767, 1995 18. Donckier V, Closset J, Van Gansbeke D, et al: Contribution of computed tomography to decision making in the management of adhesive small bowel obstruction. Br J Surg 85:1071-1074, 1998 19. Maglinte DD, Bender GN, Heitkamp DE, et al: Multidetector-row helical CT enteroclysis. Radiol Clin North Am 41:249-262, 2003 20. Maglinte DD, Heitkamp DE, Howard TJ, et al: Current concepts in imaging of small bowel obstruction. Radiol Clin North Am 41:263-83, 2003 21. Bender GN, Timmons JH, Williard WC, et al: Computed tomographic enteroclysis: One methodology. Invest Radiol 31: 43-49, 1996 22. Bender GN, Maglinte DD, Kloppel VR, et al: CT enteroclysis: A superfluous diagnostic procedure or valuable when investigating small-bowel disease? AJR Am J Roentgenol 172: 373-378, 1999 23. Beall DP, Fortman BJ, Lawler BC, et al: Imaging bowel obstruction: A comparison between fast magnetic resonance imaging and helical computed tomography. Clin Radiol 57:719724, 2002 24. Davis SE, Sperling L: Obstruction of the small intestine. Arch Surg 99:424-426, 1969 25. Frazee RC, Mucha P Jr., Farnell MB, et al: Volvulus of the small intestine. Ann Surg 208:565-568, 1988 26. Otamiri T, Sjodahl R, Ihse I: Intestinal obstruction with strangulation of the small bowel. Acta Chir Scand 153:307-310, 1987 27. Sarr MG, Bulkley GB, Zuidema GD: Preoperative recognition of intestinal strangulation obstruction: Prospective evaluation of diagnostic capability. Am J Surg 145:176-182, 1983 28. Shatila AH, Chamberlain BE, Webb WR: Current status of diagnosis and management of strangulation obstruction of the small bowel. Am J Surg 132:299-303, 1976 29. Balthazar EJ, Bauman JS, Megibow AJ: CT diagnosis of closed loop obstruction. J Comput Assist Tomogr 9:953-955, 1985 30. Balthazar EJ, Birnbaum BA, Megibow AJ, et al: Closedloop and strangulating intestinal obstruction: CT signs. Radiology 185:769-775, 1992
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31. Ha HK, Park CH, Kim SK, et al: CT analysis of intestinal obstruction due to adhesions: Early detection of strangulation. J Comput Assist Tomogr 17:386-389, 1993 32. Ha HK: CT in the early detection of strangulation in intestinal obstruction. Semin Ultrasound CT MR 16:141-150, 1995 33. Ha HK, Kim JS, Lee MS, et al: Differentiation of simple and strangulated small-bowel obstructions: Usefulness of known CT criteria. Radiology 204:507-512, 1997 34. Barnett WO, Petro AB, Williamson JW: A current appraisal of problems with gangrenous bowel. Ann Surg 183:653659, 1976 35. Laws HL, Aldrete JS: Small-bowel obstruction: A review of 465 cases. South Med J 69:733-734, 1976 36. Zalcman M, Sy M, Donckier V, et al: Helical CT signs in the diagnosis of intestinal ischemia in small-bowel obstruction. AJR Am J Roentgenol 175:1601-1607, 2000 37. Balthazar EJ, Liebeskind ME, Macari M: Intestinal ischemia in patients in whom small bowel obstruction is suspected: Evaluation of accuracy, limitations, and clinical implications of CT in diagnosis. Radiology 205:519-522, 1997 38. Frager D, Baer JW, Medwid SW, et al: Detection of intestinal ischemia in patients with acute small-bowel obstruction due to adhesions or hernia: Efficacy of CT. AJR Am J Roentgenol 166:67-71, 1996 39. Taourel PG, Fabre JM, Pradel JA, et al: Value of CT in the diagnosis and management of patients with suspected acute small-bowel obstruction. AJR Am J Roentgenol 165:11871192, 1995 40. Horton KM, Fishman EK: The current status of multidetector row CT and three-dimensional imaging of the small bowel. Radiol Clin North Am 41:199-212, 2003 41. Frager DH, Baer JW, Rothpearl A, et al: Distinction between postoperative ileus and mechanical small-bowel obstruction: Value of CT compared with clinical and other radiographic findings. AJR Am J Roentgenol 164:891-894, 1995 42. Bizer LS, Liebling RW, Delany HM, et al: Small bowel obstruction: The role of nonoperative treatment in simple intestinal obstruction and predictive criteria for strangulation obstruction. Surgery 89:407-413, 1981 43. Menzies D, Ellis H: Intra-abdominal adhesions and their
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prevention by topical tissue plasminogen activator. J R Soc Med 82:534-535, 1989 44. Burkill G, Bell J, Healy J: Small bowel obstruction: The role of computed tomography in its diagnosis and management with reference to other imaging modalities. Eur Radiol 11:14051422, 2001 45. Ijiri R, Kanamaru H, Yokoyama H, et al: Obturator hernia: The usefulness of computed tomography in diagnosis. Surgery 119:137-140, 1996 46. Blachar A, Federle MP: Internal hernia: An increasingly common cause of small bowel obstruction. Semin Ultrasound CT MR 23:174-183, 2002 47. Miller PA, Mezwa DG, Feczko PJ, et al: Imaging of abdominal hernias. Radiographics 15:333-347, 1995 48. Maglinte DD, Gourtsoyiannis N, Rex D, et al: Classification of small bowel Crohn’s subtypes based on multimodality imaging. Radiol Clin North Am 41:285-303, 2003 49. Caroline DF, Herlinger H, Laufer I, et al: Small-bowel enema in the diagnosis of adhesive obstructions. AJR Am J Roentgenol 142:1133-1139, 1984 50. Reijnen HA, Joosten HJ, de Boer HH: Diagnosis and treatment of adult intussusception. Am J Surg 158:25-28, 1989 51. Delabrousse E, Bartholomot B, Sohm O, et al: Gallstone ileus: CT findings. Eur Radiol 10:938-940, 2000 52. Balthazar EJ, Schechter LS: Air in gallbladder: A frequent finding in gallstone ileus. AJR Am J Roentgenol 131: 219-222, 1978 53. Ko S, Lee T, Ng S: Small bowel obstruction due to phytobezoar: CT diagnosis. Abdom Imaging 22:471-473, 1997 54. Eggermont E: Gastrointestinal manifestations in cystic fibrosis. Eur J Gastroenterol Hepatol 8:731-738, 1996 55. Pawel BR, de Chadarevian JP, Franco ME: The pathology of fibrosing colonopathy of cystic fibrosis: A study of 12 cases and review of the literature. Hum Pathol 28:395-399, 1997 56. Lloyd-Still JD, Beno DW, Kimura RM: Cystic fibrosis colonopathy. Curr Gastroenterol Rep 1:231-237, 1999 57. Seror D, Feigin E, Szold A, et al: How conservatively can postoperative small bowel obstruction be treated? Am J Surg 165:121-125, 1993 58. Turner DM, Croom RD III: Acute adhesive obstruction of the small intestine. Am Surg 49:126-130, 1983