Hong Kong Journal of Emergency Medicine Accuracy of plain abdominal radiography in the differentiation between small bowel obstruction and small bowel ileus in acute abdomen presenting to emergency department X SH Kim, KN Park, SJ Kim, CK Eun, YM Park, MK Oh, KH Choi, HJ Kim, DW Kim, HJ Choo, JH Cho, JH Oh, HY Park Introduction: Our purpose was to evaluate whether plain abdominal radiography (PAR) could accurately differentiate between small bowel obstruction (SBO) and small bowel ileus (SBI) in an emergency setting. We also evaluated the value of known classic signs on the PAR for differentiating between SBO and SBI. Methods: This retrospective study included 216 emergency room patients who had small bowel distension (maximal small bowel diameter ≥2.5 cm) on the PAR and who underwent successive abdominal computed tomography. One radiologist and one emergency physician retrospectively reviewed PAR in consensus, unaware of the patients' clinical data; they divided the patients into an SBO group and an SBI group according to the radiographic findings. Presence or numeric values of 10 radiographic signs were also recorded. Final diagnoses of SBO and SBI were established by a combined analysis of medical charts, surgical records, radiographic findings on abdominal computed tomography, and small bowel studies. The differential diagnoses based on PAR and the final diagnoses were compared, and the sensitivity and specificity of PAR were calculated. We also evaluated the differences among 10 radiographic signs between the final SBO and SBI groups. Results: Sensitivity and specificity of PAR for SBO were 82.0% and 92.4%, respectively. Among the 10 radiographic signs, all except maximal colon diameter were statistically significant predictors on the final Correspondence to: Park Kyu Nam, MD Seoul St. Mary's Hospital, Department of Emergency Medicine, The Catholic University of Korea, 505 Banpo-dong, Seocho-gu, Seoul 137-701, Republic of Korea Email: [email protected]Kim Han Joon, MD Inje University Haeundae Paik Hospital , Department of Emergency Medicine, 1435 Jwa-dong, Haewondae-gu, Busan 612-030, Republic of Korea Kim Suk Hwan , MD Cho Joon Ho, MD Oh Je Hyuk, MD Park Ha Young, MD Inje University Haeundae Paik Hospital , Department of Radiology, 1435 Jwa-dong, Haewondae-gu, Busan 612-030, Republic of Korea Kim Suk Jung, MD Eun Choong Ki, MD Inje University Busan Paik Hospital, Department of Radiology, Radiology, 633-165 Gaegeum 2(i)-dong, Busanjin-gu, Busan, 614-735, Republic of Korea Park Young Mi, MD Kim Dong Wook, MD Choo Hae Jung, MD Inje University Busan Paik Hospital , Clinical Trial Center, 633-165 Gaegeum 2(i)-dong, Busanjin-gu, Busan, 614-735, Republic of Korea Oh Min Kyung, PhD Uijeongbu St. Mary's Hospital , Department of Emergency Medicine, The Catholic University of Korea, 65-1 Geumo-dong, Uijeongbu-si, Gyeonggi-do, 480-717, Republic of Korea Choi Kyung Ho, MD
Accuracy of plain abdominal radiography in the differentiation between
small bowel obstruction and small bowel ileus in acute abdomen
presenting to emergency department
SH Kim, KN Park, SJ Kim, CK Eun, YM Park, MK Oh, KH Choi, HJ Kim, DW Kim, HJ Choo, JH Cho, JH Oh,
Introduction: Our purpose was to evaluate whether plain abdominal radiography (PAR) could accuratelydifferentiate between small bowel obstruction (SBO) and small bowel ileus (SBI) in an emergency setting.We also evaluated the value of known classic signs on the PAR for differentiating between SBO and SBI.Methods: This retrospective study included 216 emergency room patients who had small bowel distension(maximal small bowel diameter ≥2.5 cm) on the PAR and who underwent successive abdominal computedtomography. One radiologist and one emergency physician retrospectively reviewed PAR in consensus,unaware of the patients' clinical data; they divided the patients into an SBO group and an SBI groupaccording to the radiographic findings. Presence or numeric values of 10 radiographic signs were also recorded.Final diagnoses of SBO and SBI were established by a combined analysis of medical charts, surgical records,radiographic findings on abdominal computed tomography, and small bowel studies. The differential diagnosesbased on PAR and the final diagnoses were compared, and the sensitivity and specificity of PAR were calculated.We also evaluated the differences among 10 radiographic signs between the final SBO and SBI groups.Results: Sensitivity and specificity of PAR for SBO were 82.0% and 92.4%, respectively. Among the 10radiographic signs, all except maximal colon diameter were statistically significant predictors on the final
Correspondence to:Park Kyu Nam, MD
Seoul St. Mary's Hospital, Department of Emergency Medicine,The Catholic University of Korea, 505 Banpo-dong, Seocho-gu,Seoul 137-701, Republic of KoreaEmail: [email protected]
Kim Han Joon, MD
Inje University Haeundae Paik Hospital, Department ofEmergency Medicine, 1435 Jwa-dong, Haewondae-gu, Busan612-030, Republic of KoreaKim Suk Hwan , MD
Cho Joon Ho, MD
Oh Je Hyuk, MD
Park Ha Young, MD
Inje University Haeundae Paik Hospital, Department ofRadiology, 1435 Jwa-dong, Haewondae-gu, Busan 612-030,Republic of KoreaKim Suk Jung, MD
Eun Choong Ki, MD
Inje University Busan Paik Hospital, Department of Radiology,Radiology, 633-165 Gaegeum 2(i)-dong, Busanjin-gu, Busan,614-735, Republic of KoreaPark Young Mi, MD
Kim Dong Wook, MD
Choo Hae Jung, MD
Inje University Busan Paik Hospital, Clinical Trial Center,633-165 Gaegeum 2(i)-dong, Busanjin-gu, Busan, 614-735,Republic of KoreaOh Min Kyung, PhD
Uijeongbu St. Mary's Hospital, Department of EmergencyMedicine, The Catholic University of Korea, 65-1 Geumo-dong,Uijeongbu-si, Gyeonggi-do, 480-717, Republic of KoreaChoi Kyung Ho, MD
Kim et al./Differentiating small bowel obstruction from ileus 69
Small bowel distension (maximal small bowel diameter≥2.5 cm) on plain abdominal radiography (PAR)indicates the presence of a small bowel disorder withimpaired transit of intestinal contents.1-7 This disorderis commonly subdivided into small bowel obstruction(SBO), which result from intrinsic luminal obstructionor extrinsic compression, and small bowel ileus (SBI),which result from intestinal autonomic nervous systemdysfunction, eventually delaying the transit of intestinalcontents.1,8
Abdominal computed tomography has recently beenregarded as a more accurate imaging tool than PAR indifferentiating between SBO and SBI,8-10 but PAR isstill advocated by some authors as the initial modalityof choice for such differentiation.4,6,11-13 However, itwould be inappropriate to apply the results of priorstudies directly to an emergency setting, because thosestudy populations were limited to patients who wereclinically suspected of having SBO or who were in apost-operative period.
Recent research has raised questions concerning theeffectiveness of known classic signs (such as air-fluid
levels and differential air-fluid levels) on PAR fordifferential diagnosis between SBO and SBI.2,14-16 And,to our knowledge, clinical differences between SBOand SBI have not been previously investigated.
Small bowel distension on PAR is frequently foundamong patients with abdominal pain visiting theemergency room. For these patients, differentiationbetween SBO and SBI is crucial to decide treatment.17,18
Although class ic plain radiographic s igns fordifferential diagnosis between SBO and SBI arecommonly used by physicians, the effectiveness of thesesigns on differential diagnosis has not been vigorouslystudied.2,15,16,19 Awareness of their real effectivenessmight facilitate correct diagnosis. In addition,awareness of the clinical differences between SBO andSBI might help physicians to establish a diagnosis andpredict the patient's prognosis.17
The purpose of our study was to evaluate the accuracyof PAR in differentiating between SBO and SBI inemergency room patients complaining of abdominalpain. We modulated the classic signs into simplifiedforms that can be easily used in an emergency setting,and we evaluated their effectiveness. We also evaluatedthe clinical differences between the two groups.
diagnosis. Conclusions: PAR is an accurate and effective initial imaging modality for differentiating betweenSBO and SBI in an emergency setting, and most of the classic radiographic signs have a diagnostic value.(Hong Kong j.emerg.med. 2011;18:68-79)
X PAR SBOSBI PAR 216 PAR
≥2.5PAR SBO SBI
PAR 10 X PAR SBO82.0% 92.4% 10 X
PAR SBO SBIX
Keywords: Dilatation, intestinal pseudo-obstruction, X-ray film
Hong Kong j. emerg. med. Vol. 18(2) Mar 201170
We conducted a retrospective review of radiologicfindings and medical charts for those patients who hadabdominal pain and small bowel distension on PAR.This study was conducted at the emergency room of atertiary referral university hospital in South Korea. Thestudy period was from January 2008 to June 2008.This study was approved by our institutional reviewboard, and informed consent was waived.
We confined the study group to patients who hadundergone both erect and supine PAR views, takinginto consideration the possible influence of positionon the radiographic findings. We further confined thestudy group to patients who had undergone successiveabdominal computed tomography in order to enhancethe accuracy of the final diagnosis and to facilitateconfirmation of the causative disease.5,6,8-13,20-22
We selected 10 radiographic signs that can be easilyapplied in the emergency setting from among theknown classical signs for differential diagnosis betweenSBO and SBI.1-3,7,15,16,19,23 These signs included air-fluidlevel, differential air-fluid level, string-of-beads sign,
stretch sign, decreased colon gas, number of air fluidlevels, number of differential air-fluid levels, maximalwidth of air-fluid level, maximal small bowel diameter,and maximal colon diameter (Table 1).
One radiologist and one emergency physician with 7years of experience reviewed the radiographs togetherwithout any knowledge of the patients' clinical data;they evaluated the presence or numeric value of the10 radiographic signs in consensus. Air-fluid levels,differential air-fluid levels, string-of-beads sign, stretchsign, and decreased colon gas were documented asbeing present or absent (existence or non-existence).The number of air fluid levels, differential air-fluidlevels, maximal width of air-fluid level, maximal smallbowel diameter, and maximal colon diameter weredocumented in the form of numeric values. Only air-fluid levels that measured more than 10 mm indiameter were counted in the number of air-fluid levels,small air-fluid levels that measured less than 10 mm indiameter were classified as string-of-beads sign (Figures1 and 2).
Some ambiguity of standards was inevitable becauseno definite diagnostic cut-off values currently exist.
Table 1. The definitions of the 10 radiological signs for differential diagnosis between small bowel obstruction and small bowelileus
Radiological signs Definitions
Air-fluid levels A sharp flat horizontal line representing the interface betweengas density above and fluid density below.
Differential air-fluid levels Two different air-fluid levels in the same small bowel segment.
String-of-beads sign Air-fluid levels measured as less than 10 mm in diameter. Theytypically arrange consecutively like string-of-beads.
Stretch sign Abnormal distension of predominantly fluid-filled small bowelloop where the luminal gas has a striped appearanceoriented perpendicular to long axis of the bowel.
Decreased colon gas Diffuse decrease or absence of gas in the colon loop.
No. of air-fluid levels The number of air-fluid levels that measured more than10 mm in diameter.
No. of differential air-fluid levels The number of differential air-fluid levels.
Maximal air-fluid level width (mm) The width of largest air-fluid level.
Maximal small bowel diameter (mm) The diameter of maximally distended small bowl loop.
Maximal colon diameter (mm) The diameter of maximally distended colon loop.
Kim et al./Differentiating small bowel obstruction from ileus 71
Figure 1. Erect view of an abdominal radiograph of a 55-
year-old man with small bowel obstruction due to post-
operative adhesion. There are five air-fluid levels (short
arrows) and two differential air-fluid levels (long arrows).
Differential air-fluid level is depicted by two different air-
fluid levels in the same small bowel segment. Maximal air-
fluid level width is measured as 75 mm (line A). Maximal
small bowel diameter is measured as 53 mm (line B). Maximal
colon diameter is measured as 36 mm (line C).
Figure 2. Erect and supine view abdominal radiographs of a 58-year-old man with small bowel obstruction due to bezoar. String-
of-beads sign (arrow in erect view) is depicted by air-fluid levels measured as less than 10 mm in diameter. Stretch sign is depicted
by abnormal distension of predominantly fluid-filled small bowel loop where the luminal gas has a striped appearance oriented
perpendicular to the long axis of the bowel (arrows in supine view).
Hong Kong j. emerg. med. Vol. 18(2) Mar 201172
The final diagnoses of SBO and SBI were establishedby a combined analysis of medical charts, surgicalrecords, and radiographic findings on abdominalcomputed tomography studies and small bowel series.We placed surgical records and radiographic findingson abdominal computed tomography first.7,8,24-27
In addition, we recorded any history of previousabdominal surgery, performance of emergencyabdominal surgery, occurrence of death, and causativedisease noted on medical records.
The differential diagnoses based on PAR were comparedwith the final diagnoses, and the sensitivity and specificityof PAR were calculated. The relationships between theradiographic signs and the final diagnoses were studiedby univariate analysis and logistic regression analysis.A receiver operating characteristic (ROC) curve wasdrawn to calculate the cut-off values of numeric signsthat had shown statistically significant results. Finally, astepwise binary logistic regression analysis was performedto establish the significant predictors for diagnosis. Forthis process, numeric form signs were converted tocategorical form by using the cut-off values.
We compared the existence or non-existence ofprevious abdominal surgery history, performance ornon-performance of emergency abdominal surgery, anddeath or life between the two groups by a Pearson'schi-square test or a Fisher's exact test. Compositionaldifferences of causative diseases between the two groupswere simply compared.
Statistical analyses were performed using SPSS 11.5(SPSS Inc, Chicago, Illinois, USA) and SAS 9.1.3 (SASInst i tute , Cary, NC, USA). We ass igned thesignificance level as p<0.05.
From January 2008 to June 2008, 1355 adult patientswith abdominal pain visited the hospital's emergencyroom. Seven hundred and forty one patients hadundergone PAR (both erect and supine views) andsuccessive abdominal computed tomography within 48hours. Of these 741 patients, 216 patients who had
small bowel distension on PAR were included in thefinal study population.
Of the 216 patients enrolled in this study, 127 patientswere male and 89 patients were women. Their meanage was 58 years (range=16-88 years, standarddeviation=16.4 years). On PAR, 47 patients wereassessed as having SBO and 169 patients were assessedas having SBI. Final diagnoses were established byanalysing clinical courses and abdominal computedtomography findings in 142 patients; clinical courses,abdominal computed tomography, and surgicalfindings in 73 patients; and clinical course, abdominalcomputed tomography, and small bowel studyfindings in one patient. Fifty patients were finallydiagnosed as having SBO and 166 patients as havingSBI (Figure 3).
Among the 50 patients whose final diagnosis was SBO,41 were assessed as SBO on PAR. Among the 166patients whose final diagnosis was SBI, 160 wereassessed as SBI on PAR. Consequently, the sensitivityand specificity of PAR were 82.0% and 96.4%,respectively.
All the signs, except maximal colon diameter, showedsignificant statistical association with the finaldiagnoses (p<0.001) (Table 2). The AUCs of ROCcurves were 0.884 for number of air-fluid levels, 0.805for number of differential air-fluid levels, 0.881 formaximal air-fluid level width, and 0.871 for maximalsmall bowel diameter (Figure 4). As determined byROC curve analysis of the statistically significantnumeric form signs, cut-off values for discriminatingSBO were as follows: more than 2 levels in number ofair-fluid levels, more than 1 level in number ofdifferential air-fluid levels, more than 31.5 mm inmaximal air-fluid level width, and more than 37.5 mmin maximal small bowel diameter (Table 3).
In the stepwise binary logistic regression analysis,presence of differential air-fluid levels and presence ofstretch sign, maximal air-fluid level width more than31.5 mm, maximal small bowel diameter more than37.5 mm were significant independent predictingfactors for final diagnosis (Table 4).
Kim et al./Differentiating small bowel obstruction from ileus 73
Figure 4. Receiver operation characteristic curves of numeric signs with statistical differences between small bowel obstruction
and small bowel ileus.
Figure 3. Flow-chart showing summary of the study result.
Maximal small bowel diameter ≥37.5 mm 74% 89% 23.40 10.52 52.04 <0.0001
*Real value calculated by SPSS
Table 4. The result of the stepwise selection of logistic regression test to select more effective radiographic signs for differentiating
small bowel obstruction
Signs Odds ratio 95% Confidence interval p-value
Presence of differential air-fluid levels 4.90 1.34 17.97 0.0165
Presence of stretch sign 26.67 3.67 193.56 0.0012
Maximal air-fluid level width ≥31.5 mm 8.56 2.53 28.95 0.0006
Maximal small bowel diameter ≥37.5 mm 4.00 1.29 12.40 0.0163
Table 5. Comparison of clinical factors between small bowel obstruction and small bowel ileus
Clinical factor Small bowel obstruction Small bowel ileus p-valueNo. of patients (%) No. of patients (%)
Previous abdominal surgery 36 (72) 32 (19.3) <0.001*
Emergency abdominal surgery 28 (56) 53 (31.9) 0.002*
Death 2 (4) 4 (2.4) 0.624†
Total 50 (100) 166 (100)
*Result of Pearson's chi-square test; †Result of Fisher's exact test
Kim et al./Differentiating small bowel obstruction from ileus 75
The existence or non-existence of previous abdominalsurgery history and performance or non-performanceof emergency abdominal surgery showed statisticallysignificant differences (p=0.001, 0.002). In contrast,death or life did not show statistically significantdifferences between the SBO and SBI groups on finaldiagnosis (p=0.624) (Table 5).
Post -operat ive adhes ive i l eus cases were theoverwhelming majority for causative disease of SBO(56%), and inguinal hernia, umbilical hernia,intussusception, inflammatory bowel disease, tumour,abscess, and foreign body causing mechanicalobstruction in the bowel cavity were less frequentcauses. The causative diseases of SBI were relativelyevenly distributed although hepato-biliary disease,appendicitis, and gastroenteritis were slightly moreprevalent than others (Table 6).
The definition and classification of small boweldisorders with impaired transit of intestinal contentshave been confusing. Diverse classifications and termshave been used in the clinical field. Some apply "ileus"only to the functional disorder and others apply it toboth structural and functional disorders.1,2,8,28,29 SBO,mechanical obstruction, mechanical ileus, andobstructive ileus have been used as terms that mean asmall bowel disorder with impaired transit of intestinalcontents due to intrinsic luminal obstruction orextrinsic compression. In contrast, SBI, non-obstructive ileus, adynamic ileus, paralytic ileus, andpostoperative ileus have all been used as terms thatmean a small bowel disorder with impaired transit ofintestinal contents due to functional impairment.1,2,7,8,28,29
Some authors subdivide SBI into spastic ileus,hypotonic ileus, and paralytic ileus according to themechanism of abnormal motility. Some authors do notuse the bisectional concept of SBO and SBI, butinstead use gradual classification of normal small bowelgas pattern, abnormal but nonspecific small bowel gaspattern, probable small bowel obstruction pattern, anddefinitive small bowel obstruction pattern.7,30,31 Despitethe controversies mentioned above, using the termsSBO and SBI seems rational, because the presence or
absence of structural obstruction is the most importantconsideration in clinical decision making, and thissimple bisectional classification is widely used in theclinical field and can prevent confusion regarding theuse of the term "ileus" among physicians.
In our study of emergency department patients whohad abdominal pain and small bowel distension on thePAR, the sensitivity and specificity of PAR for SBOwere 82.0% and 96.4%, respectively. These results arefar superior to the results of other plain radiographicstudies conducted with patients clinically suspected ofhaving SBO (sensitivity 63-77%, specificity 50-78%).4,9,12
Moreover these results nearly approach some of thereported sensitivities and specificities of abdominalcomputed tomography studies.4,9,12,32 According to ourresults, PAR should be regarded as a valuable initialtool in the emergency setting for differential diagnosisof small bowel disorders with impaired transit ofintestinal contents. PAR is better in excluding SBO(diagnosing SBI) than in diagnosing SBO, because itsspecificity is superior to its sensitivity.
Since Frimann's classic study,14 air-fluid level anddifferential air-fluid level have been used to detectSBO. However, succeeding investigators viewed thesesigns as non-specific, although more frequent in SBO,because these signs could also be seen in cases of SBI.1
Other signs such as the string-of-beads sign, the stretchsign, and decreased colon gas have not been verified asspecific.2 Recently, Lappas et al2 and Thompson et al16
evaluated the effectiveness of various classic signs onPAR through subdivision and numeric conversion ofthese signs. The subjects of these studies were limitedto patients clinically suspected of having SBO, incontrast to our study, which included any emergencyroom patients with small bowel distension on PAR andabdominal pain. The study by Lappas et al2 was alsodifferent from ours in that they subdivided small boweldisorders into high-grade SBO versus low-grade SBOand SBI.
In our study, most of the plain radiographic signs werefound to occur significantly more frequently in thefinal SBO group than in the final SBI group. Thesedifferences were more prominent in our study than inthe results of other studies.2,15,16 In our study, only
Hong Kong j. emerg. med. Vol. 18(2) Mar 201176
Table 6. Comparison of causative diseases in small bowel obstruction and small bowel ileus
Small bowel obstruction Small bowel ileusCausative disease − No. of patients (%) Causative disease − No. of patients (%)
Radiation enteritis − 1 (2%) 10. Ampulla of vater cancer − 3 (1.8%)
Small bowel cancer − 1 (2%) Pancreatic cancer − 3 (1.8%)
Pelvic inflammatory disease − 3 (1.8%)
11. Bile peritonitis − 2 (1.2%)
Colon cancer − 2 (1.2%)
Colon perforation − 2 (1.2%)
Hepatitis − 2 (1.2%)
Gastrointestinal bleeding − 2 (1.2%)
Liver laceration − 2 (1.2%)
Ovarian tumour − 2 (1.2%)
Peritoneal carcinomatosis − 2 (1.2%)
Stomach cancer − 2 (1.2%)
12. Aortic dissection − 1 (0.6%)
Biliary hamartoma − 1 (0.6%)
Biliary stricture − 1 (0.6%)
Cecal cancer − 1 (0.6%)
Corpus luteum rupture − 1 (0.6%)
Esophageal rupture − 1 (0.6%)
Intestinal Behcet's disease − 1 (0.6%)
Irritable bowel syndrome − 1 (0.6%)
Ischaemic colitis − 1 (0.6%)
Malaria − 1 (0.6%)
Mesenteric tumour − 1 (0.6%)
Ovarian cancer − 1 (0.6%)
Peritoneal tuberculosis − 1 (0.6%)
Total 50 patients (100%) Total 166 patients (100%)
Kim et al./Differentiating small bowel obstruction from ileus 77
maximal colon diameter was not significantly differentbetween the two groups (p=0.2516); this result wascontrary to the study of Thompson et al16 in whichexpanded co lon f ind ings were s i gn i f i cant lymore frequent with SBI than with SBO. Furtherinves t igat ion i s warranted to determine theeffectiveness of using a finding of collapsed colon as adiagnostic factor for SBO.
Lappas et al2 reported that the incidences of string-of-beads sign were not significantly different betweenhigh-grade SBO versus low-grade SBO and SBI (39%and 23%, respectively; p=0.15). Thompson et al16 alsoreported that the incidence of string-of-beads sign wasmerely 10% in SBO and 1.7% in SBI although asignificant difference was present between the twogroups (p<0.001). Contrary to these results, in ourstudy the difference in the incidences of string-of-beadssign was significant and prominent (26% in the finalSBO group, 1.2% in the final SBI group; p<0.001).Harlow et al15 reported that the frequencies ofdifferential air-fluid levels were 52% in the SBOgroup and 29% in the SBI group. In our study, amore pronounced difference in the frequencies ofdif ferentia l a ir- f luid levels was demonstratedbetween the two groups (64% for SBO and 4.2%for SBI; p<0.001).
The specificity of each numeric sign exceeded itssensitivity at cut-off value points on the ROC curves.This suggests that numeric signs are more effective inthe exclusion of SBO than in its inclusion. Thisconclusion is consistent with the overall greaterspecificity than sensitivity of the PAR reading in ourstudy.
The incidences of previous abdominal surgery historyand emergency abdominal surgery performance weresignificantly more frequent in the SBO group than inthe SBI group. This seems to be reflective of the factthat a large number of the final SBO-group patientsunderwent adhesionolysis due to post-operativeadhesions. The incidence of death was not significantlydifferent between the two groups, which may implyan absence of a direct relation between the generalcondition of the patient and presence or absence ofintestinal obstruction.
Miller et al33 reported the most frequent causativediseases of SBO in this order: post-operative adhesion,inflammatory bowel disease, and malignant tumour.Laws and Aldrete et al34 reported the frequency in theorder of post-operative adhesion, malignant tumour,and hernia. In our study, post-operative adhesion wasthe most common causative disease of SBO, althoughthe frequency we found (56%) was lower than in thefrequencies found in the prior studies (74% and 69%).Our study found hernia and malignant tumour werethe next most common causative diseases (10% each).The frequency of inflammatory bowel disease wasrelatively low compared to the results of prior studies;this is likely due to racial differences in the distributionof this disease between Oriental and Western patients.SBI is caused by dysfunction of the intestinalautonomic nervous system due to per i tonealinflammation, ascites, pain, haemodynamic instability,drug reaction, electrolyte imbalance, trauma, or othercauses.1,2,35 Individual frequencies of SBI in patientswith abdominal pain, appendicitis, and cholecystitishave been mentioned in previous studies,18,36,37 but webelieve our study is the first to investigate the typesand frequencies of causative diseases in SBI. In ourstudy, there was an even distribution of the abdominaldiseases that were found to be causative of SBI. Thismight be explained by the fact that most abdominaldiseases are accompanied by one or more factors thatcan cause dysfunction of the intestinal autonomic nervesystem, including peritoneal inflammation, ascites,pain, haemodynamic instability, and electrolyteimbalance. The incidences of biliary disease andtumour were relatively high in our study, while theincidence of non-specific abdominal pain was relativelylow. This finding may be the result of the generallyhigh disease severity of this study group originatingfrom the emergency room of a tertiary referral hospital.
Although small bowel studies such as enteroclysis havebeen regarded as one of the most accurate radiographicexaminations for the diagnosis of SBO, these studiesare not suitable for emergency services because of theyare time-consuming.7,24-27 With the recent widespreaduse of multi-detector computed tomography, thesensitivity of computed tomography in the diagnosisof SBO has been reported as nearly 100%.6,38 Giventhat computed tomography can also identify the cause
Hong Kong j. emerg. med. Vol. 18(2) Mar 201178
of SBO, it is regarded as the most appropriate finalradiographic examination available during emergencyservices.5,7-10,12,13,20-22,39,40 Among the non-surgical casesin our study, computed tomography was used as theactual standard for final diagnosis, with the exceptionof one patient who underwent a small bowel study.
Although PAR is the most rapid and the mostconvenient radiographic examination in the initialevaluation of abdominal pain, there have recently beenmany controversies concerning its effectiveness. Someauthors advocate computed tomography as a moreeffective initial radiographic examination than PAR forpatients with abdominal pain.18,40-42 However, routineperformance of computed tomography on all patientswith abdominal pain is difficult to carry out, due topractical limitations such as delay of the treatmentprocess, increased radiation exposure, and increasedmedical expense. Using PAR to examine componentsthat it best detects or differentiates can be effective forreducing the demand for abdominal computedtomography.
There were several limitations to our study. First,because it was a retrospective design, selection bias wasinevitable. Furthermore, selection bias could have beengenerated from the inclusion criteria of successiveabdominal computed tomography, which might implythat our study population showed increased diseaseseverity. Second, only one radiologist participated as areviewer. However, adding the clinical experience ofan emergency physician to the interpretation mightlead to more relevant results for the intention of thisstudy than would the co-review of multiple radiologistssince our study was targeted to an emergency roomsetting. Third, the degree of bowel obstruction wasnot assessed. However, from the point of view ofemergency treatment, accurate screening of patientswith SBO and rapid referral of these patients toa surgeon was more impor tant than fur therdiscrimination between high-grade SBO and partialSBO.
In conclusion, PAR is a valuable initial radiographicexamination in the differentiating SBO from SBI, andthe diagnostic accuracy of PAR nears that of computedtomography. Most of the classic radiographic signs
(except decrease of colon diameter) are useful ondifferentiating between SBO and SBI among patientssuffering from small bowel dilatation as shown onX-ray.
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