AJR:168, May 1997 1171

Review Article

The Role of Radiology in the Diagnosis of Small-BowelObstructionDean 0. T. Maglinte1, Emil J. Balthazar2, Frederick M. Kelvin1, Alec J. Megibow2

T he patient with acute abdominalpain represents one of the mostcommon, most important, and most

difficult practical problems that the general sur-geon has to face [I]. Intestinal obstruction isresponsible for approximately 20% of surgicaladmissions for acute abdominal conditions [2].The small bowel is involved in 60-80% ofcases of intestinal obstruction. In spite ofadvances in imaging and a better understandingof the pathophysiology of the small bowel, its

obstruction is still frequently misdiagnosed [3].The value of diagnostic imaging in such

assessments lies in its ability to answer ques-tions relevant to the clinical management ofpatients. According to Herlinger and Maglinte[4], the issues of concern to the surgical man-agement of small-bowel obstruction that diag-nostic procedures must address are theconfirmation or exclusion of obstruction; theidentification of the site, severity, and cause ofthe obstruction; and the possible presence ofstrangulation. Underlying these questions is

the pivotal issue of whether early laparotomyis indicated or whether a trial of nonoperativemanagement should be instituted. Radiology.because it is able to supply relevant answers tomany of these questions, assumes considerableimportance in this decision. The issue of howto use imaging resources in the midst of theongoing changes in health care delivery hasconsiderable practical importance. An errone-ous choice of diagnostic procedures adds tothe costs of workup and may delay diagnosis.

This review examines the recent contributionsof radiology, addresses controversies. and rec-ommends an approach for the diagnostic triageof patients with possible intestinal obstruction.

Clinical Considerations and Controversiesin Management

To function as consultants, radiologistsmust understand surgical tenns, the clinicallimitations in diagnosing intestinal obstruc-tion, and the controversies in the surgical man-agement of this condition.

Some of the most frequently used descrip-tive terms by surgeons [2] are simple obstruc-tion, in which the blood supply to the affectedarea of bowel is intact; strangulation obstruc-tion, in which the obstructed bowel is isch-ernie because of its entrapment in a confined

space. which in turn interferes with thevenous or arterial circulation to the involvedsegment; partial obstruction, in which somegas and intestinal contents pass through thepoint of obstruction; complete obstruction, inwhich the lumen is totally occluded; closed-loop obstruction, or occlusion of a segment ofbowel at both ends (usually associated withstrangulation); low small-bowel obstruction,situated in the distal small bowel; highsmall-bowel obstruction, involving the proxi-mal small intestine; obturation obstruction,caused by an intraluminal mass such as abezoar or gallstone; and functional obstruc-tion, in which symptoms of mechanical

obstrt.iction occur without actual occlusion orcompression of the intestinal lumen. Func-tional or pseudoobstruction can be associatedwith niotility disorders. can occur as aresponse to extrinsic factors (i.e., peritonitis),or niay he idiopathic.

The pattern of major causes of small-bowelobstruction has changed during the last livedecades I I 1. Adhesions and hernias are the twomajor causes, closely followed by rnalignan-cies-most of them nieta.stases. For all practicalpurposes. these three entities account forapproximately 80/c of all cases [2). with adhe-sions accounting for as high as 79m/ in somereports [5-81. In a report of patients with small-bowel obstruction after abdominal surgery (ormalignancy, 62% had cancer-related obstruc-tion and 38#{176}7chad nonmalignant obstruction 9).A miscellaneous group of causes of small-bowel obstruction includes inflammatory pro-cesses. intussusception, volvulus, congenitallesions. gallstones. foreign bodies or bezoars.trauma, and the occasional iatrogenic obturation

obstruction by a distended hallixin of a feedingor decompression tube 141-

The diagnosis of intestinal obstructiondepends on the classic tripod: a carefully takenhistory. a meticulous physical examination.and special investigations 111. Of the last, radi-ology is the most iniportant.

The clinical accuracy of diagnosingmechanical small-bowel obstruction is highwhen the findings of crampy abdominal pain.distention, vomiting. and obstipation are

Received June 27, 1996; accepted after revision September 16, 1996.1 Department of Radiology, Methodist Hospital of Indiana and Indiana University School of Medicine, 1701 N. Senate Blvd., Indianapolis, IN 46202. Address correspondence to D. D. T.Maglinte.

2Department of Radiology, New York University Medical Center, New York, NY 10016.

AJI? 1997;168:1 171-1180 0361-803X/97/1685-1 171 American Roentgen Ray Society

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1172 AJR:168, May 1997

present together with plain film findings of

small-bowel distention with multiple air-fluidlevels and decreased gas and fecal material [ I I.Unfortunately. in approximately one third ofcases, plain abdominal radiography does notconfirm the clinical findings to allow a confi-dent diagnosis of mechanical small-bowelobstruction and. in addition, often fails to

answer questions about management. If theplain film finding is unrevealing or ifearly sur-gical intervention is not performed in patients

with probable obstn.iction, further imaging isoften indicated (4. 10).

The nianagement of patients with adhesivesmall-bowel obstruction remains a controver-

sial subject. If the ohstn.iction is partial. aninitial trial o)f intestinal decompression is fre-quently recommended by surgeons in thebelief that this approach is safe and that theneed for surgery can he avoided 5-J. Othersurgeons believe that early surgical interven-

tion is necessary. especially with completeobstruction, both because of the difficulty indistinguishing simple from strangulatedobstruction and because of the high compli-cation rate associated with delayed operativeintervention 111-141. The timing of such sur-gery is probably most controversial inpatients with adhesive obstruction because

the success rate of avoiding operation by the

use of gastrointestinal tithe decompression inthese patients is high 12. 15. 161. The currentmortality rate o)f patients with adhesiveobstruction is in the l-2/c range 116. 171.

suggesting that the risks associated with con-servative management may be acceptableprovided that the operation can be promptlyperformed when deterioration or strangula-tion is clinically evident. Unfortunately. clini-cal experience has shown that simplemechanical obstruction cannot be reliablydifferentiated from strangulated obstructionon the basis of clinical, laboratory. and plainfilm findings 18. 12. 14, 18-211. Of patientswith surgically proven strangulation. the pre-operative diagnosis is unreliable in 50_85C/c

IS. 22-261. The mortality rate of strangula-tion complicating small-bowel obstruction isapproximately 25%. Thus, mortality andmorbidity from intestinal obstruction con-

tinue to be significant [21.

Fig. 1.-Sudden onset of constant ab-dominal pain and nausea in 54-year-oldman who had undergone laparotomy.A and B, Emergent supine (A) and up-right (B) abdominal radiographs shownormal intestinal gas pattern.C, Emergency CT study reveals residualair in right colon (open arrow) and tran-sition zone with collapsed loop of ileum(so/id arrows) suggestive of high-gradesmall-bowel obstruction. Seen in leftlowerabdomen are fluid-filled distendedclosed loops (c) and extraintestinal fluidindicating hemorrhage in mesentery at-tached to distended loops (H), featureshighly suspicious for strangulation. Atsurgery, adhesions and closed-loop ob-struction were identified and segment ofischemic bowel was resected.

Plain Abdominal RadiographyIn spite of advances in imaging. plain film

examination has remained the starting pointin the radiologists involvement in theworkup of patients with intestinal obstruction1271. Plain film findings are estimated to bediagnostic in about 50-60% of cases; equivo-

cal in about 20-30%; and normal, nonspe-

cific. or misleading in 10-20% of cases 15,18-20]. The lack of a definition for the vari-ous terms used in describing intestinal gaspatterns on plain films has resulted in consid-erable confusion [28, 291. Emergency physi-cians frequently use the term nonspecific

abdominal gas pattern to mean normal [3].One survey showed that 70% of radiologistsused the term 128]. Sixty-five percent of these

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AJR:168, May 1997 1173

interpreted this to mean normal or probablynormal. whereas 22% interpreted this tomean cannot tell if normal or abnormal andI 3% interpreted this to mean abnormal butcannot tell if it represents mechanicalobstruction or adynamic ileus.

In a recent analysis of plain film examina-tions in diagnosis of small-bowel obstructionby experienced gastrointestinal radiologists.a sensitivity of only 66% was found 1101.This report differed from other studies in thatthe various plain film patterns were delinedand a follow-up for every defined interpre-tive category was given. In this report 62c/cof the patients clinically suspected of havingsmall-bowel obstruction did not in fact haveobstruclion. Of patients with plain films

interpreted as having normal findings. 21 C4had low-grade small-bowel obstruction: ofthose patients with findings interpreted to heabnormal hut nonspecific. 13% had low-grade and 9% had high-grade small-bowelobstruction; and of those patients with find-

ings interpreted to show probable small-

hovcl obstruction. 37% had low-grade andI 6/ had high-grade small-bowel o)hstntc-tioti. No) complete siiiall-hovel o)hstructionswere seen in the lhree categories. Ofthe find-ings interpreted as showing definite small-bowel o)hstructlon. 264 had low-grade uul23C4 had high-grade sinaI I-bowel obstruction

itid I 3Yc had complete small-bowel ohstnic-tion. This report indicates a pattern that isneither normal nor fits the categories ofprobably or deli n itely obstructed. (amm illand Nice [301 recogniied this pattern tomean ileus (i.e.. the small bowel is unable to)push fluid along). Indeed, the word iletismeans stasis and does 1101 differentiatehetv CC1 mechanical and no)nnlechanio.alcauses. Small-bowel stasis has been pro-posed to describe this pattern. o)r if the termnonspecific abdominal gas pattern is usedat all. it should he qualified as abnormal 3l[.This interpretation satisfies a group of plainfilm findings that does not fit the normal and

dcli ii i telv ahnornial categories and has c I i ii i -cal i nipl ications.

The literature clearly docunients significaniliiiiitations o)fthe phtin filni esaiiiinatioii iii thediagnosis and tsscssnlent of degree of intestintl

o)hstructio)n [4[. Niost pltieilts with stispectedsiiil I -ho vel ohstriiction iiioi a nornil ptttenl

o)r dii abnormal but no)nspecific pllteril illhave no o)hstnict oil or lov-giadc )hsi ruct i ni1 10[. A nlulo)rity. however, have high-gradeo)hstflictions atid i ccasional lv strangulatingobstruction (Fig. 1). In addition to) having alow sensitivity to) detectio)n on plain film radi-ography, mechanical and functional colonico)hstniction can present with radiographicfindings suggesting small-bowel obstruction

132 I. Isolated d istent ion of the small h welhas been observed in I 64 o)f paticilts witho)hstnicting colon carcinoma (Fig. 2. and dis-tention together with air-fluid levels in thesmall bowel has been shown in 26C4 ofpatients with colonic pscudoohstniction 133.341. The diagnosis of small-bowel obstruction

Fig. 2.-Abdominal pain and right lower quadrant fullness in 61-year-oldman who had never undergone laparotomy.A and B, Supine (A) and erect (B) abdominal radiographs show dilated smallbowel with air-fluid levels and empty colon consistent with mechanicalsmall-bowel obstruction.C, CT scan obtained after A and B reveals distended loops of small bowelwith air -fluid levels (s( and extensive circumferential thickening of wall ofcecum (c), compatible with cecal carcinoma. Inflammatory changes andfluid are seen in adlacent mesentery (I). At surgery, 10-cm cecal carcinomawith pericolic inflammation and edema was resected.

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1174 AJR:168, May 1997

Ofl plain films when the loops are predomi-nantly fluid-filled is an acknowledged inter-pretive dilemma. Inability to appreciate subtleplain film evidence of fluid-filled small bc,wel

(string-of-pearls sign, stretch sign, or pseudo-tumor sign) is still common in practice [3].Thus, the detection of pertinent plain filmfindings (air-filled distended small bowel, dif-ferential fluid levels. empty colon. free air inperitoneal cavity) has significant clinicalvalue that greatly contributes to the initialdiagnostic and therapeutic decision making.However, the absence of these findings isassociated with a low negative predictivevalue and cannot be relied on in clinical prac-tice. In the workup of patients with suspectedintestinal obstruction, plain films interpretedas showing noniial findings or small-bowelstasis (abnormal but nonspecific) are notreliable and should be used with caution inthe context of a comprehensive clinical evalu-ation. If the clinical suspicion of intestinalobstruction is high or if a variety of otherabdominal conditions that can mimic bowelobstruction are clinical possibilities. additionalimaging niay be required to explain the clini-cal presetitation. Despite these limitations.

plain film radiography remains a mainstay inthe evaluation of suspected small-bowelobstruction because of its high sensitivity inrevealing higher grades of small-bowel ob-struction, its widespread availability. and itsrelative inexpensiveness [271.

Barium Examination in Small-BowelObstruction

Experience accumulated mainly in the lasttwo decades has shown that the intubation infu-siOil method of examining the small intestine(enteroclysis or the small-bowel enema) hasimproved the preoperative diagnosis of patientswith suspected small-bowel obstruction 135-441. The small-bowel follow-through with bar-ium or water-soluble contrast material, evenwhen done meticulously, has been shown tohave significant inherent limitations in thediagnosis of small-bowel obstruction [35, 36].Distensibility and fixation of the small bowelare difficult to assess. Partially obstructinglesions may pnx.luce only a fleeting moment ofprestenotic dilatation, which can be difficult toappreciate with limited fluoroscopy. In highergrades of obstruction, contrast material is oftenretained in the stomach and filling of the smallbowel is delayed and incomplete. Because ofretained fluid in the small bowel proximal tothe site of obstruction, contrast material isincreasingly diluted and mucosal detail is mad-

Fig. 3.-Unexplained recurrent nausea, abdominal pain,and weight loss in 45-year-old woman who had under-gone hysterectomy 5 years earlier and in whom plain filmradiography, conventional small-bowel follow-through,and CT had been unrevealing. Radiograph obtained dur-ing enteroclysis shows mild distention of small bowel upto segment in right lower abdomen (curved arrow)where fixation and diminished caliber of more distal pel-vic segments are consistent with partial obstruction.Scattered areas of peritoneal adhesions manifested byabrupt angu)ation or tenting (straight arrows) and adhe-sive band fixation (arrowhead) are seen. All folds are de-fined clearly, indicating low-grade partial obstructionassociated with diffuse pelvic adhesions. Findings at sur-gery for recurrent symptoms confirmed diagnosis. (Re-printed with permission from 138])

equate. Therefore, the value of the small-bowelfollow-through in patients with suspected acutemechanical sniall-bowel obstruction is limited.

However. of the different imaging methods thatdo not test luminal distention, the small-bowelfollow-through done fluoroscopically is a via-

ble alternative to enteroclysis in the assessmentof low-grade obstruction because fixation ofsegments can be tested during intermittent fiuo-roscopy [36, 371.

The frequent intennittent fluoroscopic moni-tonng during enteroclysis contrast infusion

makes assessment of fixed and nondistensiblesegments easier to recognize. The effects ofnild obstruction are exaggerated (Fig. 3). Thelevel and cause of most obstructing lesions areprecisely shown by enteroclysis. In a recentreport. enteroclysis correctly predicted the pres-ence of obstruction in l(XY/c of cases, theabsence of obstruction in 88%, the level ofobstruction in 89%, and the cause of obstruc-tion in 86% 1101. An important advantage ofenteroclysis compared with other imagingmethods is its ability to gauge the severity ofobstruction objectively 110. 38]. The amount ofcontrast material traversing the point of obstruc-ti()n can be helpful information in decidingwhether to continue nonoperative nianagement

Fig. 4-39-year-old woman with recurrent lower abdo-men pain who had undergone hysterectomy 5 years ear-her and in whom plain film radiography, small-bowelfollow-through, and CT had been unrevealing. Enterocly-sis shows fixed pelvic segments of ileum that were im-movable during cephalad angled compression atfluoroscopy (not shown). Scattered areas of peritonealadhesions manifested by multiple linear defects(arrowheads) associated with adhesive band fixationare seen. Terminal ileum is of smaller caliber than moreproximal segments. Laparoscopy confirmed that smallbowel was fixed to vaginal cuff and posterior wall of un-nary bladder by multiple adhesions. Laparoscopic lysis ofadhesions resulted in relief of symptoms. C = cecum. (Re-printed with permission from 137])

Or to perforni iniiiiediate operation. In partialsniall-bowel obstruction, enteroclysis has beenshowii to be approximately 85% accurate indistinguishing adhesions from metastases,tumor recurrence. and radiation damage [39[.Enteroclysis has been advocated as the defini-tive study in patients about whom the diagnosisof low-grade inteniittent small-hciwel obstruc-tioti is clinically uncertain 1421. Its ability toboth reveal low-grade small-bowel obstructionand exclude the possibility of small-bowelobstruction niakes it an inpo)rtant tool in thisdifficult clinical problem [40-1-t[ (Fig. 4).

The tenhl closed-loop obstruction is con-strued by illOst surgeons as indicating a coin-plete. acute obstruction. It portends a progressionto infarction, indicating the need for urgent sur-gery. The clinical diagnosis of this entity is unre-liable I 19-23[. Ifa patient has clinical findings ofperitoneal irntation. fever. or leukocytosis. (Fshould be the initial choice of imaging. AfterCT. however, if additional infonnation is clini-cally desired (e.g.. how much contrast material isgoing through the site of obstruction) or if addi-tional clarification of cause is needed. enterocly-sis is complementary [27. 451 (Fig. 5).Enteroclysis has been shown to) reveal partialclosed-loop obstruction [46, 471.

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Fig. 5.-31-year-old woman who had been unrestrained passenger in motor vehicle accident 3 months earlier andsustained liver and spleen lacerations, multiple pelvic bone fractures, and head injury with subsequent developmentof hydrocephalus and presented with vomiting after feedings.A, Supine abdominal radiograph is unremarkable except for revealing gasless left hemiabdomen and few gas-filledloops of small bowel in right hemiabdomen. Feeding tube tip seen in proximal jejunum was introduced through non-functioning endoscopic gastrostomy port. Ventriculopenitoneal shunt is seen in right hemiabdomen.B, CT study shows multiple dilated small-bowel loops. Transition zone is in right hemiabdomen (arrow points to col-lapsed but contrast-filled loop distalto obstruction). Findings were consistent with partial small-bowel obstruction as-sociated with adhesions.C, Enteroclysis was requested after 2 days of nasogastnic suction to assess severity of obstruction. After positioningof decompression and enteroclysis tube in jejunum, additional 12 hr of suction was done because offluid retained injejunum. Supine radiograph reveals interval passage of fecal debris in colon but persistent distention of small bowel.D, Infusion of contrast medium after inflation of balloon (straight arrow) distal to feeding tube reveals area of narrow-ing in proximal jejunum (curved arrow), producing obstruction. Dilated bowel immediately distal to obstruction sug-gests either closed-loop obstruction or multiple points of obstruction.E, Delayed radiograph 3 hr later shows second point of obstruction (open arrow) near site of proximal obstruction(curved arrow) with no contrast material beyond, suggesting either high-grade multiple adhesive band obstruction orclosed-loop obstruction. Surgery revealed two separate high-grade proximal and distal small-bowel adhesive bandobstructions that were lysed. Patient was able to resume tube feedings.

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1176 AJR:168, May 1997

For enteroclysis in patients with small-bowel obstruction, the use of a catheterdesigned to allow decompression has beenhelpful for patients who may need continuedmechanical decompression after the enterocly-sis [48]. Such a catheter spares the patient thetrauma of reintubation with the larger standardSalem sump nasogastric tube. This tube is bet-ter tolerated by patients and, as opposed toother long tubes. can be positioned in the prox-imaljejunum without difficulty [49].

The main disadvantages of enteroclysis arethe need for nasoenteric intubation and theslow transit ofcontrast material in patients witha fluid-filled hypotonic small bowel, that is, inhigh-grade obstruction. The need for the radiol-ogist to be continuously involved with the pro-cedure and for conscious sedation makesenteroclysis impractical in the outpatient (non-hospital) clinic setting. Many institutions alsolack individuals with the proper expertise. Ifexpertise in performance of enteroclysis islacking, a dedicated small-bowel follow-through with tluoroscopic monitoring every I 5to 30 mm until the right colon is reached is anacceptable substitute for the evaluation ofsmall-bowel obstruction, provided no high-grade obstruction is present [36. 37].

In patients with unsuspected complete orhigh-grade small-bowel obstruction. bariumexaminations may be difficult because of thelong time required to complete the examina-tion. The dilution of barium that occurs proxi-mal to the site of obstruction makes diagnosticevaluation suboptimal. Moreover. bariumretained in the small bowel will degrade thediagnostic quality of subsequent CT examina-tion. Therefore, in the acute presentation, (1should be the method of examination.

CT in Small-Bowel ObstructionThe recent literature has documented the

growing and important role of CT in the pre-operative evaluation of patients with sus-pected intestinal obstruction. Initial reports ofCT in small-bowel obstruction by Megibow etal. [50J and Fukuya et al. 1511 showed a sensi-tivity varying from 90% to 96%, a specificityof 96%, and an accuracy of 95%. Thesereports. however, appeared to be mostly onpatients with high-grade obstruction. In a crit-ical analysis of the reliability of CT byMaglinte et al. [38], in which an equal numberof patients with high and low grades of small-bowel obstruction were assessed, less favor-able results were shown. Overall sensitivitywas 63%; specificity, 78%; and accuracy.66%. However, when small-bowel obstruc-

tion was classified into high and low grades.CT had a sensitivity of 8 1 % for high-gradeand 48% for low-grade obstruction, thus vali-dating the accuracy of CT in high-gradesmall-bowel obstruction. Further experienceconfirms these results [27].

The speed and ability of CT to reveal thecause ofobstruction makes it particularly valu-

able in the acute setting (Figs. I and 2). CT isable to correctly reveal the cause of obstruc-tion in 73-95% of cases [27, 38. 50, 5 1j andcan show both closed-loop obstruction andstrangulation [52-6 11. This concern is mostsignificant for surgeons who might choosenonoperative measures to manage a patientwith small-bowel obstruction. Although con-trast-enhanced CT has a high sensitivity (90%)in the diagnosis of intestinal ischemia, its spec-ificity is low (44%) [61]. The negative predic-tive value of 89% reported in a prospectivestudy by Frager et al. [61] is encouraging. Ahigh negative predictive value in diagnosingclosed-loop obstruction and strangulationshould help resolve the controversy aboutwhether urgent operation or longer nonsurgi-cal measures are appropriate in patients withadhesive small-bowel obstruction 1621. Earlyreports on the ability ofCT to differentiate var-ious causes of bowel distention were promis-ing [50, 51]. More recent reports document theability of CT to differentiate small-bowelobstruction from ileus or other causes ofsmall-bowel dilatation [63, 64]. The report byGazelle et al. [63] on the efficacy ofCT in dis-tinguishing small-bowel obstruction fromother causes of small-bowel dilatation showeda retrospective sensitivity of 84%. In high-grade small-bowel obstruction. Frager et al.[64] showed the sensitivity of CT to be 100%compared with 46% for plain film radiogra-phy. The impact of CT in the management ofsmall-bowel obstruction in the acute settingwas recently addressed in a clinical study byTaourel et al. [53]. By differentiating paralyticileus from obstruction, radiologists used CTfindings to modify management in 21% ofpatients either by changing conservative man-agement to a surgical one (18%) or by chang-ing surgical management to a conservative one(Fig. 6). Thus, Cl can expedite the need forsurgery and also avoid unnecessary operation,an important goal in the management of adhe-sive small-bowel obstruction. The importanceof CT in the acute clinical setting has beenrecently emphasized by Balthazar [54]. CT isparticularly helpful and should be used as theprimary imaging technique in patients inwhom the obstructive symptoms are associ-ated with specific medical conditions such as

previous abdominal malignant tumors, knowninflammatory bowel disease, palpable abdomi-

nal mass. or sepsis.Whether oral contrast material should be

routinely given for CT has not been ade-quately addressed in the current literature. IfCT is performed when plain film radiographyshows definite or probable small-bowelobstruction, oral contrast material may not benecessary. A scrutiny of the illustrations inreviewed citations that show CT images ofhigher grades of small-bowel obstruction mdi-cate that fluid is already present in largeamounts in the small bowel and acts as aninherent contrast agent. The presence ofintraluminal fluid and the increased attenua-tion of the intestinal wall following theadministration of IV contrast agents allows amore accurate assessment of the thickness ofthe intestinal wall [65] (Fig. 1C). The use oforal contrast material increases the attenuationof intraluminal fluid and may occasionallymake difficult the determination of wall thick-ening (Fig. SB). The use of oral contrast mate-rial can also delay examination in thisemergent situation. In addition, in the subsetof patients with high-grade obstruction, oralcontrast material will not usually reach thesite of obstruction at the time of examination(Fig. 2C). Furthermore, these patients havebeen vomiting and the administration of addi-tional fluid should be discouraged. However,when CT is performed on patients with nor-mal or abnormal but nonspecific plain filmfindings. oral contrast material administeredthrough a decompression tube is recom-mended. Its use enhances the accuracy ofdiagnosing neoplastic or inflammatory intesti-nal lesions, or intraabdominal abscesses, andallows better evaluation of the degree ofobstruction in patients with partial small-bowel obstruction. In the patient with theprobable small-bowel obstruction pattern,when the clinical background is vague, CTshould be performed before fluoroscopicstudies. In this way, it will not interfere withsubsequent enteroclysis if needed.

Significant advantages of CT over enterocly-sis are that CT is readily available, rapid, does

not require technical expertise, is noninvasive,and allows a global evaluation of the entireabdomen and alimentary tract. The last advan-tage is of considerable importance, particularlyin the acute setting, because intestinal obstruc-tion is only one of the more common differentialdiagnoses in the patient presenting with acuteabdominal pain. The impact of CT on the diag-nosis and treatment of the acute abdomen hasbeen shown by Siewert and Raptopoulos [66].

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Fig. 6-66-year-old woman with abdominal pain and vomiting who hadundergone hysterectomy 10 years earlier and recent mitral valve surgery.(Reprinted with permission from 1651)A, Supine abdominal radiograph following 24 hr of nasogastnic suction re-veals findings unequivocal for small-bowel obstruction. Enteroclysis wasordered to gauge severity of presumed adhesive obstruction. CT was in-stead recommended by radiologist following placement of long tube forfurther decompression.B and C, CT sections through upper (B) and lower (C) pelvis show fluid-filleddilated small bowel and collapsed colon. Small-bowel dilatation terminatedat incarcerated obturator hernia (arrow, C). Demonstration of internal her-nia changed planned medical regime to urgent surgical intervention. Find-ings were confirmed at surgery. No strangulation was present

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AJR:168, May 1997 1177

However, a learning curve is associated with theinterpretation of CT in intestinal obstruction.The CT examination should be closely moni-tored, and additional sections should be obtainedat the transition zone (the area of sudden changeof caliber of small-bowel loops from dilated tocollapsed or normal. indicating the site ofobstruction) to elucidate the cause of obstructionif unclear with the contiguous axial 10-mm sec-tions. Identifying the transition zone is not diffi-cult in higher grades of obstruction. In low-gradepartial obstruction. however, identifying thetransition zone can be difficult as a result of con-fusion in following the bowel loops in and out ofthe axial images [67]. Cine paging has been sug-gested by Memel and Berland [681 as an aid indiagnosis. Where difficulty exists in identifying

the site and cause of obstruction by CT. entero-clysis is informative [37].

CT enteroclysis. a method whereby water-soluble contrast material is infused fluoroscop-ically and continued during cross-sectionalimaging. has been recently described by

Bender et al. [691. Theoretically. the techniqueovercomes the low reliability of CT for thediagnosis of low-grade small-bowel obstruc-

tion and uses the ability of CT to reveal the

cause of obstruction. which has potential clini-cal application for small-bowel obstruction.Additional clinical experience is needed todefine the role of this method.

Although the evidence is preliminary, theability of CT to reveal closed-loop obstructionand to show evidence of infarction is likely to

be the most significant contribution of imaging

in the management of acute small-bowelobstruction. If CT is used appropriately, its ini-

tially higher cost may result in overall costsavings within an episode of care by expedit-ing or avoiding surgery and reducing comor-bidity and length of stay.

RecommendationsIn the workup of small-bowel obstruction,

the radiologist, clinician, and surgeon shouldcommunicate directly with one another. Selec-tion of imaging techniques is based on fullknowledge of the clinical background. history.physical examination, and laboratory exami-natio)n as well as plain film findings.

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Clinical BackgroundPatient history. physical and laboratory examinations

.1Suspected Intestinal Obstruction

IPlain Abdominal Radiography

Normal or Abnormal butand Probable SBO 1

a

+

CT

-EniocIsis s -:: tiif- if it L enteroclysis not

infbnnatiye infbnnative

1178 AJR:168, May 1997

Fig. 7.-Diagram shows algorithm for diagnostic triage of patients with suspected intestinal obstruction. SBO = small-bowel obstruction.

The acknowledged limitations of the plainfilm examination. the advantages and limita-

tions of bariuni examinations and CT. andthe lack (if specificity and reliability of clini-cal and laboratory findings form the basis ofthe algorithni we propose for the evaluationof patients with suspected intestinal obstruc-tion (Fig. 7). Barium small-bowel and abdomi-nal CT examinations are not competitive butcomplementary studies. The dilemma thatfaces radiologists is not to select one tech-

nique and eliminate the other but to decidewhich to use first in the context of the clini-

cal presentation and abdominal plain filmfindings 154. 65).

An interpretation of definite small-bowelobstruction on plain film radiography con-firms the clinical diagnosis and helps in thedecision on whether to perform surgery or usea trial of conservative therapy. This decisionis largely based on the clinical evaluation (his-tory. physical examination, and laboratoryexamination), and many of these patients havelaparotomy without an additional imagingstudy. Factors that may lead to eaily suigicalexploration include an incarcerated hernia,

absence of previous abdominal surgery. coin-plete small-bowel obstruction, and clinicalsigns suspicious for strangulation such as con-stant abdominal pain. fever. elevated WBC.increased serum amylase. and metabolic aci-dosis. Factors that tend to delay or obviate

surgical intervention are partial small-bowelobstruction, previous small-bowel obstructionwith adhesions. a history of resected abdoini-nal tumor. and a history of inflamiiiatorybowel disease. When initial conservativemanagement is entertained. CT examinationis helpful in evaluating the presence andextent of neoplastic or inflammatory diseaseand in excluding strangulating obstruction(Fig. 6). Postsurgical patients presenting withabdominal distention are treated conser a-

tively for a few days. and CT examination isadvised only if the clinical and plain film find-ings do not improve or signs of sepsis or pan-creatitis develop. Barium examination shouldbe used after the CT study only if additionaliimnagement questions are left unanswered[27. 47] (Fig. 5).

If the plain film shows colonic distention inaddition to small-bowel dilatation, we stilladvise the use of contrast enema as the nextimaging technique (Fig. 8). In this group ofpatients. CT is used as a complementary tech-nique. particularly in elderly infirm patients. inindividuals with sepsis. and in patients with a

history of previously resected colon carci-

noma. CT is also useful in the acute setting inpatients with poor anal sphincter tone 134 I-

When the disparity between the clinicalpresentation and the plain film fiuidiiigs isstriking, an additional imaging study is indi-

cated to elucidate the diagnosis amid plan for

surgical or medical therapy. In patients withnormal or with abnoriiial but nonspecific

(sniall-bowel stasis) plain film findings whopresent with acute abdominal symptoms(emergency patients). we advise the use ofCT. CT has been reliable in showing acuteabdominal conditions that can mimic small-

bowel obstruction. has a high sensitivity forhigh-grade or complete obstruction. and can

reveal closed-loop and strangulating obstruc-tioil (Figs. I and 2). When the CT examina-tiOfi is not diagnostic. enteroclysis or afluoroscopy-based barium small-bowel study

can be performed as a complementary exami-nation (Fig. 5). On the other hand, patientscomplaining of niild. intermittent abdominal

pain. often labeled as irritable bowel syn-drome (outpatient. clinic environment), with-out a pertinent history except for previouslaparotomy. should have enteroclysis or a flu-

oroscopy-based small-bowel follow-throughexamination as the next imaging technique.Low-grade obstructions. intraluminal tumors,small ulcerations, and mucosal inflammatorychanges can often be detected and better eval-uated with this technique (Figs. 3 and 4). Inthese individuals, CT can be performed laterif the barium small-bowel examination is not

informative or is uncertain.The indications for ordering diagnostic pro-

cedures are undergoing intense scrutiny

because of the need to control health care costs

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Diagnosis of Small-Bowel Obstruction

AJR:168, May 1997 1179

Fig. 8.-Use of contrast enema for intestinal obstruction in 65-year-old man with abdominal distention, pain, and constipation and prior sigmoid resection for diverticulitis. (Reprintedwith permission from [651)A, Supine abdominal radiograph shows gas-distended cecum (arrow) in addition to small-bowel distention.B, Single-contrast barium enema shows obstructing carcinoma (arrow).

without comproniising a high standard ofpatient care. Radiologic services are now eval-uated by criteria that assess whether the use ofa particular diagnostic method influences din-ical nianagement. improves patient outcome.

and lowers niedical costs )70. 7 1 1. Erroneousapplication of imaging studies is frequent inclinical practice.

The recent development and improvementsin technique and interpretation of CT andenteroclysis have changed the approach to the

evaluation (if patients suspected of havingsmall-bowel obstruction. In addition to) plainfilm radiography. CT and enteroclysis play acomplementary but essential role in the initialdiagnosis and guidance for therapy. The

strength and limitations o)f alternative imagingapproaches must be well understood by bothradiologists and clinicians to achieve the goalof providing the best clinical management atminimal cost. At this time we advise the initialuse of abdominal CT in the context of the acuteabdomen (emergency patient) and the initialuse of enteroclysis or a fluoroscopy-hased

small-bowel follow-through study in mildly

symptomatic patients with chroinic complaints.

Our recommendations are based on continuingradiologic observations and clinical and radio-logic data reported in the literature over the lastone and a half decades. As additional experi-

ence with new iniaging techniques is gained.this experience should be incorporated into therecommendatio)ns. We hope that our proposedalgorithiii will expedite diagnosis. decreasemorbidity and niortality rates. and decrease thecost of workups for patients with suspected

small-bciwel obstruction.

AcknowledgmentWe thank Fran Shaul for secretarial

assi stance.

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