George W. Holmes Lecture. CT of Small-Bowel Obstruction

Transcription

1 255 CT of Small-Bowel Obstruction Emil J. Balthazar1 The diagnosis of intestinal obstruction is established or suspected on clinical grounds, and it is usually confirmed with plain abdominal radiography. Because of significant limitations in the clinical and Initial radiographic evaluations, antegrade or retrograde contrast-enhancement (barium, water-soluble media) studies are being additionally requested for about 20-30% of patients (1-6]. In the past few years, the steady advances In technology, technique, and Interpretation have increased the value of CT in diagnosing and evaluating intestinal obstruction [7-10]. Although the precise role and contribution of CT are still being investigated and remain controversial, its significant clinical impact is already generally accepted. For patients thought to have mechanical intestinal obstruction who have confusing clinical and conventional radiographic findings, CT is currently used as a complementary imaging study, in direct competition with the more traditional gastrointestinal contrast-enhanced examinations generally used. The potential contribution of CT and its role, advantages, and limitations in the diagnosis and evaluation of intestinal obstruction are explored. Background A variety of abdominal conditions can cause intestinal obstructions. The reported prevalences of these obstructions George W. Holmes Lecture vary in different series depending on the type of practice and the population of patients. About 50% of intestinal obstructions (including those ofthe colon) are caused by adhesions, 15% by external or internal hernias, and 15% by primary or secondary neoplasms. Other less common or multiple causes have been reported in the other cases [4]. On the basis of the pathophysiology of the obstructing process, mechanical intestinal obstructions are divided into two types: simple obstructions and closed-loop obstructions. Establishing the preoperative diagnosis of the type of obstruction on the basis of the clinical evaluation and plain abdominal radiographs is extremely important, albeit very difficult. Most patients with simple mechanical intestinal obstructions do not have complications, and a more conservative approach and! or a delay in surgical intervention is acceptable. Patients with closed-loop obstruction have a high prevalence of morbidity and mortality if the diagnosis is delayed and emergency laparotomy is not performed in time [11-20]. In simple obstructions, the bowel is occluded at one or several points along its course, and depending on the severity and duration of the process, the proximal part of the bowel is variably distended. Patients have abdominal distension, obstipation, colicky abdominal pain, and sometimes nausea and vomiting (Table 1). It has been estimated that plain radiographic findings are diagnostic in about 50-60% of cases; equivocal in about 20-30%; and normal, nonspecific, or misleading in 10-20% of cases [4, 21-23]. Contrastenhanced examinations are particularly useful in patients with colonic obstructions, proximal intestinal obstructions, and partial incomplete obstructions. It was reported in one series that, among the 327 patients admitted because of Received August 24, 1993; accepted after revision October 18, Presented at the annual meeting of the New England Roentgen Ray Society, Boston, April Depaftment of Radiology, New York University-Tisch-Bellevue Medical Center, 550 First Ave., New York, NY Address correspondence to E. J. Balthazar. AJR 1994;162: X/94/ American Roentgen Ray Society

2 256 BALTHAZAR AJR:162, February 1994 TABLE 1: Clinical Signs of Small-Bowel Obstruction Type of Obstruction/Signs Simple Obstipation, abdominal distension, colicky abdominal pain, nausea and vomiting Strangulation Constant abdominal pain, tachycardia, fever, peritoneal irritation, leukocytosis, hyperamylasemia, metabolic acidosis intestinal obstruction, 21 % underwent contrast-enhanced gastrointestinal studies, and useful information was obtained in about 70% of these patients [23]. The limitations of conventional gastrointestinal contrast-enhanced studies relate to the excessively long time required to complete the examination, dilution of contrast material in the intestinal contents, and inability to adequately visualize the site and cause in forms of complete obstruction or to differentiate a simple intestinal obstruction from a closed-loop obstruction. Enteroclysis can be performed relatively quickly, and it is a more reliable method of evaluating small-bowel disease. It has shown an 85% accuracy in the evaluation of small-bowel obstruction [24] but has disadvantages. It is a more invasive procedure, is difficult to perform in critically ill patients, and is contraindicated in patients with complete obstructions or in those with suspected strangulation. In closed-loop or incarcerated intestinal obstruction, a loop of bowel is occluded at two adjacent points along its course (Fig. 1). The obstruction is the result of a simple constrictive lesion that compresses the intestine but additionally involves the attached small-bowel mesentery in the process. The length of the closed loop is variable from a single to several loops of bowel. Because of the localized constriction of A Fig. 1.-Diagram of closed-loop obstruction. A, Adhesive band causes obstruction at two points of adjacent segments of bowel. B, Closed-loop obstruction associated with intestinal voivuius. Twisting of closed loop (voivulus) is a common but not invariable complication of incarcerated loop. (Reprinted with permission from Baithazar et ai. (25].) B two adjacent segments of bowel and the intervening mesentery, a narrow pedicle is formed that leads into a mobile distended closed-bowel loop. This anatomic configuration allows the closed loop to rotate (twist) along its long axis, producing a small-bowel volvulus. The volvulus tends to occur in patients with high degrees of obstruction, but once developed, it further aggravates the mechanical obstructive process and contributes to the development of mesenteric ischemia. Strangulation is defined as a closed-loop obstruction associated with intestinal ischemia. It occurs in about 10% of patients with small-bowel obstruction and has a mortality rate of 10-37% [1, 2, 11-16]. Patients have sudden development of constant, severe abdominal pain. In the more advanced cases, fever, tachycardia, leukocytosis, signs of peritoneal irritation, metabolic acidosis, and hyperamylasemia are seen (Table 1). These signs reflect the late physiologic alterations triggered by the developing necrotic tissue. In these patients, the draining mesenteric veins are occluded first, leading to severe congestive changes affecting the wall ofthe bowel and mesentery. Increased venous and capillary pressure leads to edema, rupture of small vessels, and intramural and mesenteric hemorrhage. Arterial insufficiency usually follows, aggravating the anoxia and further contributing to the rapid development of ischemia, infarction, and perforation. The severity and duration of the obstructive process determines the subsequent development of complications. Surgical examination reveals bluish discoloration of the closed loop, loss of arterial pulsations, intestinal and mesenteric hemorrhage, and lack of peristalsis, all signs indicative of anoxia and impending infarction. Strangulation is associated with adhesions or internal or external hernias. Occasionally it may develop as the consequence of an idiopathic small-bowel volvulus without associated intraperitoneal abnormality. This type of strangulation is a common surgical emergency in some African and Asian countries, but it is rarely encountered in the United States [26]. A definite distinction should always be made between closed-loop obstruction (incarceration) and strangulation (ischemia). These are related phenomena but separate pathologic entities. Strangulation always develops because of a closed loop; however, a closed loop can be only partially obstructed, may not be associated with strangulation, and can resolve spontaneously. The classic article of Mellins and Rigler [27] has defined the potential usefulness of scout abdominal films in differentiating simple from strangulated intestinal obstruction. The coffee bean sign, representing the distended air-filled closed loop; the pseudotumor sign, produced by the overly distended fluid-filled closed loop; fixation of a loop of bowel; and a nodular luminal contour of the compromised intestine are sometimes detected. These are revealing signs but are seldom seen or properly interpreted. In most cases, findings on scout abdominal films have been found to be nonspecific or deceptively normal [18-20, 28-30]. Because most patients with closed-loop obstruction and strangulation have high-grade obstructions, antegrade contrast-enhanced gastrointestinal studies are not revealing, and enteroclysis is contraindicated in the advanced cases.

3 AJR:162, February 1994 CT OF SMALL-BOWEL OBSTRUCTION 257 In the enteroclysis series of Maglinte et al. [6], only cases of low-grade obstruction, many due to external hernias and none with strangulation, are described. Extensive clinical experience has shown that simple obstruction and strangulation cannot be reliably differentiated on the basis of conventional clinical, laboratory, and plain film findings [1, 11-15]. This is because the diagnostic parameters hitherto described are not present in the early reversible stages of the disease. Furthermore, even in the advanced stages of infarction, these signs have been proved unreliable and often misleading. In patients with small-bowel obstruction, the development of strangulation cannot be diagnosed preoperatively in 50-85% of patients with surgically proved strangulation [3, 12, 16-20]. Role of CT Experience accumulated mainly in the past 5 years has shown that CT should substantially improve the preoperative diagnosis and evaluation in this clinically challenging group of patients. CT has definite advantages and certain limitations when attempting to answer three essential clinical questions about patients with suspected intestinal obstructions: (1) Is the bowel obstructed? (2) What are the level, severity, and cause of the obstruction? and (3) Is closedloop obstruction or strangulation present? Is the Bowel Obstructed? The CT diagnosis of bowel obstruction and the differential diagnosis from an adynamic ileus are based on the detection of a definite transition zone, with dilated fluid and/or air-filled loops of small bowel proximal to the site of obstruction and collapsed loops of small bowel or colon distal to the site of obstruction (Fig. 2). The amount of intraluminal air vs fluid and even the degree of dilatation of the small bowel are unreliable criteria. Fluid-filled loops as large ass cm in transverse diameter can be present in a nonobstructive ileus (Fig. 3). The distended proximal part of the bowel and the collapsed distal part of the bowel appear as continuous segments on sequential images, and a striking disproportion in size should be apparent at the site of transition (Fig. 2). The larger the discrepancy at the transition zone and the higher the degree of collapse ofthe distal loop, the more reliable and convincing the CT appearance. Previous CT reports on series of patients with high-grade intestinal obstructions have yielded sensitivities of 96% [7] and 90% [9], with a specificity of 96% and accuracy of 95% [71. In one series of patients with lower grades of small-bowel obstruction, however, the overall CT sensitivity for detection of obstruction was 63% [8]; it was 81% for high-grade and 48% for low-grade obstructions. CT has shown limitations in the diagnosis of intestinal obstruction related to several factors. Location of the obstructive process at the ileocecal valve with residual fecal contents in the colon can lead to an erroneous diagnosis of ileus. Cases of mild partial obstruction that do not exhibit a transition zone or alternative intraperitoneal abnormality are overlooked. Other causes related to technical factors include motion or streak artifacts, or decompression of the proximal part of the bowel by previous long-tube suction or residual barium in the intestinal tract that will interfere or obscure the detection of typical diagnostic CT features. Additionally, as reported by Megibow et al. [7], a source of false-positive CT findings is the detection of distended ascending and transverse portions of the colon and a totally collapsed descending colon. This pattern is seen often in patients with nonobstructed ileus and should not lead to a diagnosis of colonic obstruction unless a colonic lesion is visualized at the splenic flexure. These patients, and those in whom a strong clinical suspicion of intestinal obstruction is not confirmed with CT, should have a retrograde or antegrade contrast-enhanced examination for further evaluation. What Are the Level, Severity, and Cause of Obstruction? The exact point of obstruction is sometimes visualized as a beaklike narrowing in patients with adhesions or as an incriminating focal intestinal or adjacent intraperitoneal lesion [7-9, 31]. In most patients with obstructions produced by adhesions, Fig. 2.-Simple complete obstruction of small bowel produced by adhesions. A, CT scan shows that small bowel (B) is markedly distended and filled with fluid and air. Ascending and descending portions of colon are collapsed (arrows). B, CT scan of caudal section through pelvis shows markedly distended fluid-filled loops of small bowel (B) and totally collapsed loops of bowel at site of transition (arrows). Small amount of residual air is present in sigmoid colon (C). Exact point of obstruction and adhesions are not visualized. Fig. 3.-Nonobstructed ileus 6 days after exploratory Iaparotomy for a stab wound. CT scan shows that small-bowel loops (B) are filled with fluid and distended, measuring 5 cm in transverse diameter. Large amount of air is present in large intestine (L). Transition zone was not visualized. Patient improved with conservative therapy.

4 258 BALTHAZAR AJR:162, February 1994 the point and cause of the obstruction are not apparent. The level of the obstruction is determined by detecting the site of the transition zone (Fig. 2) and by surveying all the abdominal axial images and comparing the relative lengths of the prestenotic vs collapsed intestine. Attempting to determine the level of obstruction solely on the basis of the site of transition can be misleading. Jejunal loops can be located in the pelvis, and ileal loops can be obstructed in the upper abdomen. If, atthe level of transition, there is no apparent cause of obstruction, repeat 5- by 5-mm sections through the transition zone may show the cause of the obstruction. Failure to visualize an obstructive lesion (tumor, intussusception, inflammation, abscess, hernia) is interpreted as diagnostic of obstruction caused by adhesions. Using these criteria, Megibow et al. correctly predicted the cause of obstruction in 73% of the cases in their series [7] (Figs. 1 and 4). This percentage, although not impressive, compares favorably with the sensitivity of plain films and contrastenhanced gastrointestinal studies for determining the cause of intestinal obstruction. In surgical practice, a deliberate effort is made to differentiate partial from complete intestinal obstructions. This distinction is usually based on clinical evaluation, plain film findings [32], and the contrast-enhanced follow-through examination [33]. Most patients with partial obstructions respond to nasogastric or long-tube decompression. Furthermore, there is less urgency to operate, because in these patients the prevalence of strangulation is negligible. In a series of 91 patients presumed to have partial obstruction of the small bowel, 80 (88%) were treated successfully by nasogastric or long-tube suction [32]. Complete and partial obstruction of the small bowel are readily distinguished on CT scans by determining the degree of collapse and the amount of residual air and fluid in the collapsed intestinal segment (Figs. 2 and 4). According to established surgical precepts, patients with complete obstruction should have surgery, whereas patients with partial obstruction of the small bowel can be treated initially with a conservative approach under close clinical supervision. Obviously, in patients with partial obstructions in whom CT shows a surgically treatable intestinal or mesenteric lesion, surgery will be done. Fig. 4.-Partial small-bowel obstruction In a patient with Crohn s disease. A and B, CT scans show significant dilatation of fluid-filled loops (s) in proximal part of small bowel and a transition zone with partially collapsed distal loops (arrows). Distal lleum contains a small amount of intraluminal fluid and has a circumferentially thickened wall (arrows). Proliferation of fat is apparent In right lower quadrant. Partial small-bowel obstruction resolved with conservative therapy. in evaluating this syndrome is still untested and must be further evaluated in a larger prospective study. I believe, however, that a careful search to identify these often subtle CT findings should allow a correct preoperative diagnosis in most patients. The expected CT findings are divided into two categories: signs associated with the closed loop and signs indicative of strangulation. These signs acquire their proper significance only when CT evidence of mechanical small-bowel obstruction is present. CT Signs of Closed-Loop Obstruction The CT findings in closed-loop obstruction are related to the incarcerated loop and depend on the length, degree of distension, and orientation of the closed loop in the abdomen. Additional findings can be seen at the site of obstruction [25] (Fig. 5). Sequential cross sections through an elongated closed loop reveal a characteristic fixed radial distribution of several dilated bowel loops with the stretched and prominent mesenteric vessels converging toward the point of torsion (Table 2 and Fig. 6). In most patients, the incarcerated bowel measures 3-5 cm in diameter, but simi- Is Closed-Loop Obstruction or Strangulation Present? Several recent reports have described a variety of CT findings that, when present and properly interpreted, lead to a correct preoperative diagnosis of closed-loop and strangulated small-bowel obstruction [25,26,31, 34-37]. The reliability and accuracy of CT Fig. 5.-Diagram of closed-loop obstruction with corresponding cross-sectional images at different levels. Cranial cross sections reveal radial distribution of fluid-filled loops of bowel and engorged mesenteric vessels converging toward site of torsion. At level of torsion are two adjacent collapsed loops of bowel.

5 AJR:162, February 1994 CT OF SMALL-BOWEL OBSTRUCTION 259 lar degrees of dilatation can be present in the bowel proximal to the incarceration. When a loop of incarcerated small bowel is horizontally oriented, it will be U-shaped or C- shaped on cross section (Fig. 7). The radial distribution and the U-shaped or C-shaped configuration may be detected in the same person depending on the orientation of different small-bowel loops within the incarcerated segment of bowel. In our experience, the incarcerated loop is entirely or almost entirely filled with fluid (Figs. 6 and 7), whereas proximal intestinal loops usually contain larger amounts of air. TABLE 2: CT Signs of Closed-Loop Obstruction Incarcerated small bowel Radial distribution with stretched mesenteric vessels converging toward torsion U-shaped or C-shaped dilated bowel loop Site of torsion Two adjacent collapsed, round, oval, or triangular loops Beak sign Whirl sign Fig. 6.-Closed-loop obstruction due to adhesions proved at surgery. No strangulation (ischemia) was evident. A, Findings on plain abdominal radiograph are unremarkable. B, CT scan shows that small bowel is obstructed, with transition zone in lower part of abdomen. In mid abdomen, loops of small bowel (s) have a radial distribution with mesenteric vessels radiating toward obstructing site (arrow). Fig. 8.-Closed-loop obstruction due to internal hernia. A, CT scan shows that several loops of small bowel (b) are dilated and predominantly fluid filled. At root of mesentery, two collapsed adjacent bowel loops are imaged in cross section (arrow). B, CT scan of adjacent section shows two collapsed loops joining together, leading into site of torsion (arrow). At surgery, incarcerated bowel was viable. (Reprinted with permission from Balthazar et al. (25].) At the site of obstruction, the two adjacent narrowed loops leading into the site of torsion are visualized mainly with sequential 5- by S-mm sections as two adjacent collapsed loops usually located at the root of the mesentery (Fig. 8). The collapsed loops are round, oval, or sometimes triangular in transverse section (Fig. 8). The beak sign, seen at the site of torsion, appears as a fusiform tapering when the bowel is imaged in longitudinal section. A tightly twisted mesentery is occasionally seen in patients with volvulus and has been reported as the whirl sign [37]. In our retrospective evaluation of 19 cases of closed-loop obstruction, one or several CT signs of incarceration were detected in 15 patients [25]. CT Signs of Strangulation CT signs indicative of strangulation pertain to abnormalities involving the wall of the incarcerated bowel and to characteristic changes occurring in the attached small-bowel mesentery (Table 3). The expected changes in the bowel wall are similar to the ischemic changes previously reported [38-40]. The wall of the bowel may be slightly and circumfer- Fig. 7.-strangulated small-bowel obstruction due to adhesions. Incarcerated fluid-filled smallbowel loop (B) is C-shaped. Collapsed loops of distal part of bowel are seen at transition zone (small arrows). Fluid is seen in mesentery with obliteration of mesenteric fat and vascular structures (large arrow). This finding selectively involves segment of mesentery attached to incarcerated loop. At surgery, 45 cm of infarcted bowel was resected.

6 260 BALTHAZAR AJR:162, February 1994 TABLE 3: CT Signs of Strangulation Wall of incarcerated small bowel Slight circumferential thickening Increased attenuation Target or halo sign Pneumatosis intestinalis Attached mesentery Blurring, haziness of mesenteric vessels Obliteration of mesenteric vessels, fluid, hemorrhage entially thickened, it may show increased attenuation (Fig. 9), it may exhibit concentric rings of slightly different densities (target or halo sign) (Fig. 10), or in advanced cases pneumatosis intestinalis may develop. In the mesentery attached to the incarcerated segment of bowel, moderate to severe congestive changes and hemorrhage indicate the presence of strangulation. These findings vary in severity from increased haziness with blurring of the mesenteric vessels to total obliteration of the fatty mesentery and its vessels caused by the mesenteric hemorrhage (Figs. 7 and 10). In our series of 16 patients with proved strangulation, one or several CT signs of strangulation were detected in 10 patients [25]. The most reliable CT findings are intestinal pneumatosis and hemorrhagic mesenteric changes selectively involving the distribution of the incarcerated loop. In a recent retrospective analysis of 10 patients with strangulation, similar CT findings were reported [31]. In addition, a serrated, beaklike narrowing was described in patients with strangulation [31]. Ascites is more commonly seen in patients with strangulation, and it should be considered a Fig. 9.-Strangulated small-bowel obstruction due to adhesions. CT scan shows that small-bowel loops are distended and fluid filled. Circumferential mild thickening and increased attenuation of bowel wall (arrows) are present, as is hemorrhagic fluid in mesentery and peritoneal cavity. Hemorrhagic infarct was found at surgery, and 30 cm of bowel was resected. (Reprinted with permission from Balthazar et al. [25].) % I I I, A suspicious finding. It may be present, however, in patients with closed-loop obstruction without ischemia and in patients with simple intestinal obstruction [25, 31]. Conclusions Although CT often has been found useful in patients with suspected small-bowel obstruction, its precise role in patients treatment is still controversial, and rational guidelines for its use are not fully developed. CT has been found to be reliable for diagnosing high-grade obstruction, but it shows a relatively low sensitivity in cases of low-grade obstruction of the small bowel. At this time, we advise the use of CT in two major situations: (1) in the 10-20% of patients in whom the results of clinical and plain film examination are abnormal but nonspecific and additional imaging evaluation is required and (2) in patients in whom obstruction is associated with specific medical conditions, such as previous abdominal malignant tumors, inflammatory bowel disease, sepsis, and a palpable abdominal mass, or a clinical presentation suggestive of strangulation. Failure to detect simple small-bowel obstruction or closedloop obstruction does not rule out these conditions. In my experience, however, pertinent CT findings have proved to be valuable and clinically helpful. Patients with CT evidence of complete small-bowel or closed-loop obstruction should be closely monitored and operated on early in the course of disease. CT evidence of strangulation should lead to emergency surgery. Patients with partial, low-grade obstructions can be treated conservatively initially unless an associated surgical lesion is detected with CT. If the signs and symptoms do not resolve quickly, a contrast-enhanced gastrointestinal examination should be performed in these patients and in those in whom the initial CT findings were equivocal or nonspecific. B Fig. 10.-Strangulated small-bowel obstruction due to adhesions. A, Plain abdominal radiograph shows a poorly defined soft-tissue mass (pseudotumor) (T) in left flank (arrows) that is suggestive of strangulation. B, Cross-sectional CT scan obtained at same level as radiograph shows distended fluidfilled loop of small bowel (s) that is C-shaped. Loop of bowel has a thickened wall, and there is a suggestion of a target sign (arrow). Attached mesentery is hemorrhagic (H) and shows a high attenuation with fluid and obliteration of vascular markings. Surgery revealed mesenteric hemorrhage, and 50 cm of infarcted bowel was resected. (Reprinted with permission from Balthazar at al. [25].)

7 AJR:162, February 1994 CT OF SMALL-BOWEL OBSTRUCTION 261 ACKNOWLEDGMENT I thank Marguerite A. McKnight for manuscript preparation. REFERENCES 1. Laws HL Aldrete JS. Small bowel obstruction: a review of 465 cases. South MedJ 1976;69: Waldron GW, Hampton JM. Intestinal obstruction: a half century comparative analysis. Ann Surg 1961;153: Davis SE, Sperling L Obstruction of the small intestine. Arch Surg 1969; 99: Mucha P. Small intestinal obstruction. Surg C/in NorthAm 1987;67: Tibblin S. Diagnosis of intestinal obstruction with special regard to plain roentgen examinations ofthe abdomen. Acta ChirScandl969;135: Maglinte DT, Herlinger H, Nolan DJ. Radiologic features of closed loop obstruction: analysis of 25 confirmed cases. Radiology 1991;179: Megibow AJ, Balthazar EJ, Cho KC, Medwid SW, Birnbaum BA, Noz ME. Bowel obstruction: evaluation with CT. Radiology : Maglinte DD, Gage SN, Harmon BH, et al. Obstruction of the small intestine: accuracy and role of CT in diagnosis. Radiology 1993;188: Fukuya T, Hawes DR, Lu CC, Chang PJ, Barloon TJ. CT diagnosis of smallbowel obstruction: efficacy in 60 patients. AJR 1992;158: Stewart ET. CT diagnosis of small-bowel obstruction (commentary). AJR 1992;158: Bizer LS, Liebling RW, Delany HM, Gliedman ML. Small bowel obstruction: the role of nonoperative treatment in simple intestinal obstruction and predictive criteria for strangulation obstruction. Surgery : Sarr MG, Bulkley GB, Zuidema GD. Preoperative recognition of intestinal strangulation obstruction: prospective evaluation of diagnostic capability. Am J Surg 1983;145: Barnett WO, Petro AB, Williamson JW. A current appraisal of problems with gangrenous bowel. Ann Surg 1976;183: Lefall LD, Syphax B. Clinical aids in strangulation intestinal obstruction. Am J Surg 1970;120: Nadrowski LF. Pathophysiology and current treatments of intestinal obstruction. Rev Surg 1974;31 : Shatila AH, Chamberlain BE, Webb WR. Current status of diagnosis and management of strangulation obstruction of the small bowel. Am J Surg 1976;1 32: Silen W, Hem MF, Goldman L. Strangulation obstruction of the small intestine. Arch Surg 1962;85: Snyder EN, McCranie D. Closed loop obstruction of the small bowel. Am J Surg 1965;111 : Otamiri T, Sjodahl R, lhse I. Intestinal obstruction with strangulation of the small bowel. Acta Chir Scand 1987;153: Frazee RC, Mucha P Jr, Farnell MB, van Heerden JA. Volvulus of the small intestine. Ann Surg 1988;208: Lo AM, Evans WE, Carey LC. Review of small bowel obstruction at Milwaukee County General Hospital. Am J Surg 1986:11: Nelson SW, Christofordes AJ. The use of barium sulfate suspensions in the study of suspected mechanical obstruction of the small intestine. AJR 1967;101 : Dunn JT, Halls JM, Beme TV. Roentgenographic contrast studies in acute small bowel obstruction. Arch Surg 1984:119: Herlinger H, Maglinte DDT. Small bowel obstruction. In: Herlinger H, Maglinte DDT, eds. Clinical radiology of the small bowel Philadelphia: Saunders, 1989: Balthazar EJ, Birnbaum BA, Megibow AJ, Gordon RB, Whelan CA, Hulnick Dl-l. Closed-loop and strangulating intestinal obstruction: CT signs. Radiology 1992;185: Jaramillo D, Raval B. CT diagnosis of primary small-bowel volvulus. AJR 1986;147: Mellins HZ, Rigler LG. The roentgen findings in strangulating obstructions of the small intestine. AJR 1954;71 : Frimann-Dahl J. Radiological experiences in true strangulating obstructions. Acta Radioll95l 35: Gough IR. Strangulating adhesive small bowel obstruction with normal radiographs. BrJ Surg 1978;65: Schmidt AG. A roentgen sign in strangulating obstructions of the small intestine. Radiology 1965;85: Ha HK, Park CH, Kim 5K, et al. CT analysis of intestinal obstruction due to adhesions: early detection of strangulation. J ComputAssist Tomogr 1993; 17: Brolin RE. Partial small bowel obstruction. Surgery 1984;95: Joyce WP, Delaney PV, Gorey TF, Fitzpatrick JM. The value of water soluble contrast radiology in the management of acute small bowel obstruction. Ann R Coil Surg 1992;74: Balthazar EJ, Bauman JS, Megibow AJ. CT diagnosis of closed loop obstruction. J ComputAssist Tomogrl985;9: Cho KC, Hoffman-Tretin JC, Alterman DD. Closed-loop obstruction of the small bowel: CT and sonographic appearance. J Comput Assist Tomogr 1989;13: Fisher JK. Computed tomographic diagnosis of volvulus in intestinal malrotation. Radiology : Shaff Ml, Himmelfarb E, Sacks GA, Burks DD, Kulkami MV. The whirl sign: a CT finding in volvulus of the large bowel. J Comput Assist Tomogr 1985;9: Federle MP, Chun G, Jeffrey RB, Rayor R. Computed tomographic findings in bowel infarction. AJR 1984;142: Alpern MB, Glazer GM, Francis IR. lschemic or infarcted bowel: CT findings. Radiology 1988;166: Smerud MJ, Johnson CD, Stephens DH. Diagnosis of bowel infarction: a comparison of plain films and CT scans in 23 cases. AJR 1990;154:99-103