Radiology

Emergency Radiology Sun Ho Ahn, MD William W. Mayo-Smith, MD Brian L. Murphy, MD Steven E. Reinert, MS John J. Cronan, MD

Index terms: Abdomen, acute conditions, 70.27, 70.291, 70.46, 70.723, 70.81 Abdomen, CT, 70.12111, 70.12112 Abdomen, radiography, 70.11 Emergency radiology Published online before print 10.1148/radiol.2251011282 Radiology 2002; 225:159 –164 1

From the Department of Diagnostic Imaging, Brown Medical School and Rhode Island Hospital, 593 Eddy St, Providence, RI 02903. From the 1999 RSNA scientific assembly. Received July 26, 2001; revision requested September 17; final revision received April 1, 2002; accepted April 26. Address correspondence to W.W.M.S. (e-mail: [email protected]).

Acute Nontraumatic Abdominal Pain in Adult Patients: Abdominal Radiography Compared with CT Evaluation1 PURPOSE: To compare the diagnostic yield of abdominal radiography with that of computed tomography (CT) in adult patients presenting to the emergency department with nontraumatic abdominal pain. MATERIALS AND METHODS: Records of 1,000 consecutive patients presenting to the emergency department with acute abdominal pain from April to June 1998 were retrospectively reviewed. A total of 871 patients underwent abdominal radiography, and 188 underwent abdominal CT. The report interpretations of the abdominal radiographs and CT scans were divided into normal, nonspecific, and abnormal categories. Final discharge diagnoses were compared with the interpretations of the imaging examination results, and sensitivities and specificities of each modality were calculated and compared. RESULTS: Interpretation of abdominal radiographs was nonspecific in 588 (68%) of 871 patients, normal in 200 (23%), and abnormal in 83 (10%). The highest sensitivity of abdominal radiography was 90% for intraabdominal foreign body and 49% for bowel obstruction. Abdominal radiography had 0% sensitivity for appendicitis, pyelonephritis, pancreatitis, and diverticulitis. Sensitivities of abdominal CT were highest for bowel obstruction and urolithiasis at 75% and 68%, respectively. CONCLUSION: Abdominal radiographs are not sensitive in the evaluation of adult patients presenting to the emergency department with nontraumatic abdominal pain. ©

Author contributions: Guarantors of integrity of entire study, all authors; study concepts, S.H.A., W.W.M.S., J.J.C., B.L.M.; study design, S.H.A., W.W.M.S., S.E.R.; literature research, S.H.A., W.W.M.S.; clinical studies, all authors; data acquisition, S.H.A.; data analysis/interpretation, S.H.A., W.W.M.S., S.E.R.; statistical analysis, S.H.A., S.E.R.; manuscript preparation, S.H.A., W.W.M.S., S.E.R.; manuscript definition of intellectual content, editing, revision/review, and final version approval, all authors. ©

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RSNA, 2002

Acute abdominal pain is a common presenting symptom in the emergency department and has many underlying causes (1– 4). Although abdominal radiography has traditionally been considered an essential part of the work-up in patients with acute abdominal pain, the results are often not specific (5,6). More recently, computed tomography (CT) has been shown to be useful in the emergency department, particularly in patients with bowel obstruction, inflammatory bowel disease, renal calculi, and appendicitis (7–27). Despite the proved usefulness of CT and the poor sensitivity and specificity of abdominal radiography, physicians in the emergency department still frequently order abdominal radiography. The purpose of this study was to compare the diagnostic yield of abdominal radiography with that of CT in adult patients presenting to the emergency department with nontraumatic abdominal pain.

MATERIALS AND METHODS Three authors (S.H.A., W.W.M.S., B.L.M.) retrospectively reviewed all abdominal radiographic and CT reports in consecutive patients presenting to our level 1 trauma center with acute abdominal pain from April 12 through June 30, 1998. All of the abdominal radiographic and CT examinations were performed in the emergency department radiology 159

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suite and interpreted by board-certified radiologists. Pediatric patients (⬍18 years old) and patients with acute abdominal trauma were excluded from this study. Institutional review board approval and patient informed consent were not required by our hospital at the time of this study.

Radiography Cohort One thousand patients underwent abdominal radiography during the study period. One hundred twenty-nine (13%) of these patients were excluded because their radiology, emergency department, or hospital diagnoses could not reliably be established. Thus, the abdominal radiography cohort included 871 patients (415 men, 456 women; age range, 18 – 89 years; mean age, 49 years). We (S.H.A., W.W.M.S., B.L.M., J.J.C.) created three categories for abdominal radiographic interpretations: normal, nonspecific, and abnormal. The normal category was defined as having radiographs with a normal or negative interpretation. The nonspecific group was composed of radiographs in which no definite conclusion was reached. This group included findings such as nonspecific bowel gas pattern, nonspecific abdominal calcifications, and other such descriptions. Radiographs with diagnoses attributable to a specific cause of abdominal pain were defined as abnormal. Interpretations in the abnormal group were urolithiasis, gallstones, intraabdominal foreign body, ileus, and bowel obstruction.

CT Cohort One hundred eighty-eight patients (80 men, 108 women; age range, 19 –92 years; mean age, 52 years) underwent abdominal CT performed in the emergency department during the study period. CT was performed with use of orally and intravenously administered contrast material (READI-CAT 2 barium sulfate suspension, E-Z-Em, Westbury, NY; Omnipaque 240 and 300, iohexol, Nycomed, Princeton, NJ), unless patients were suspected of having renal calculi, and 5–10-mm section thickness was used (9800; GE Medical Systems, Milwaukee, Wis). All patients had retrievable radiology reports and admission and discharge records available for review. We (S.H.A., W.W.M.S., B.L.M., J.J.C.) grouped the CT interpretations into the following discrete categories: bowel obstruction, ileus, urolithiasis, appendicitis, diverticulitis, Crohn disease, intraabdominal abscess, 160

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Figure 1. Images obtained in a 22-year-old man with acute lower abdominal pain. (a) Supine abdominal radiograph is normal. (b) Transverse CT scan of the lower abdomen obtained with intravenously and orally administered contrast material shows extensive thickening of the terminal ileum and the cecum (arrow) consistent with Crohn disease.

abdominal aortic aneurysm, hepatobiliary disease, ischemic bowel, pyelonephritis, gynecologic disease, splenic disease, adrenal masses, pancreatic disease, intraabdominal foreign body, and other.

Clinical Diagnoses and Statistical Methods Final clinical diagnoses were defined as the discharge diagnoses from either the emergency department patient records or, for patients who were admitted to the hospital, the discharge diagnoses obtained from the hospital information system. These diagnoses were accepted as the reference standard for each case. Interpretations from the abdominal radio-

Figure 2. Images obtained in a 39-year-old man with acute lower abdominal pain. (a) Abdominal radiograph shows a normal bowel gas pattern with possible nephrolithiasis (arrows) on the right side. (b) Follow-up transverse CT scan obtained with intravenously and orally administered contrast material through the pelvis demonstrates a tubular structure (arrow) with inflammatory changes in the right lower quadrant consistent with appendicitis, which was confirmed at surgery. No renal calculus was seen.

graphs (nonspecific findings were treated as negative for each diagnostic type) and CT scans were then compared with the final discharge diagnoses. Sensitivity, specificity, and accuracy of abdominal radiography and CT were calculated separately for each of the following abdominal disorders: bowel obstruction, urolithiasis, appendicitis, pyelonephritis, pancreatitis, diverticulitis, and intraabdomAhn et al

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TABLE 1 Discharge Diagnosis in 871 Consecutive Patients Examined with Abdominal Radiography Hospital Discharge Diagnosis

No. of Patients

Abdominal pain Genitourinary disease Gastrointestinal disease Other Pancreatic disease Hepatobiliary disease Peptic ulcer disease Bowel obstruction Intraabdominal neoplasm Appendicitis Diverticulitis Gynecologic disease Foreign body Ileus Nonabdominally related

259 (30) 136 (16) 95 (11) 39 (5) 37 (4) 36 (4) 32 (4) 25 (3) 17 (2) 14 (2) 12 (1) 12 (1) 9 (1) 1 (0) 147 (17)

Note.—Data in parentheses are percentages.

TABLE 2 Discharge Diagnosis in 188 Consecutive Patients Examined with Abdominal CT Final Discharge Diagnosis Abdominal pain Urolithiasis Hepatobiliary disease Peptic ulcer disease Diverticulitis Pyelonephritis Gynecologic disease Pancreatic disease Appendicitis Bowel obstruction Gastroenteritis Abdominal neoplasm Ischemic bowel Other Nonabdominally related

No. of Patients 38 (20) 30 (16) 9 (5) 8 (4) 7 (4) 4 (2) 4 (2) 4 (2) 3 (2) 3 (2) 3 (2) 1 (1) 1 (1) 3 (2) 70 (37)

Note.—Data in parentheses are percentages.

RESULTS The results are summarized in Tables 1–5.

Radiography Cohort

Figure 3. Images obtained in a 65-year-old woman with lower abdominal pain. (a) Abdominal radiograph obtained with the patient supine demonstrates a nonobstructive bowel gas pattern. (b) Transverse CT scan obtained with intravenously administered contrast material through the pelvis reveals extensive sigmoid colonic wall thickening (arrow) and mesenteric stranding consistent with acute diverticulitis.

inal foreign body. Statistics (sensitivity, specificity, accuracy) were calculated for images in two groups: (a) all available radiographs (n ⫽ 871) and CT scans (n ⫽ 188), and (b) the subpopulation of patients (n ⫽ 120) for whom both radiographic and CT studies were available. Sensitivity calculations were based on the number of positive cases per diagnosis type as reported in Table 1 (abdominal radiography) and Table 2 (abdominal CT) and specificity, on the total minus the number of positive cases. Exact binomial CIs are presented with sensitivity and specificity values. All statistics were calculated by using commercially available software (Stata version 7; Stata, College Station, Tex). Volume 225

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Five hundred eighty-eight (68%) of 871 abdominal radiographs were interpreted as nonspecific. Nonspecific bowel gas pattern, nonspecific abdominal calcifications, and other results accounted for 48%, 15%, and 4% of the nonspecific cases, respectively. Results in 200 (23%) of 871 examinations were normal. Eighty-three (10%) of 871 patients had a specific diagnostic abnormality. Abnormal diagnoses included bowel obstruction (4%), urolithiasis (2%), ileus (2%), abdominal foreign body (1%), and gallstones (1%). No cases of intraperitoneal free air or appendicolithiasis were observed. The distribution of hospital discharge diagnoses for patients who underwent abdominal radiography is illustrated in Table 1. Abdominal pain without an identifiable cause was the most common discharge diagnosis: 259 (30%) of 871 patients. Patients with nonabdominally related discharge diagnoses accounted for 17% (147 of 871) of patients. The discharge diagnoses of genitourinary, gastrointestinal, pancreatic, hepatobiliary, and peptic ulcer diseases were seen in decreasing order. The sensitivity and specificity of abdominal radiography were calculated for each discharge diagnosis, and these values are listed in Table 3. Abdominal radiography

displayed highest sensitivity in depiction of intraabdominal foreign body (90%) and bowel obstruction (49%). For bowel obstruction, urolithiasis, ileus, and intraabdominal foreign body, specificities ranged between 98% and 100%.

CT Cohort Results in 38 (20%) of 188 CT examinations were normal, and 150 (80%) patients had a specific diagnosis. The distribution of CT diagnoses was as follows: urolithiasis, 34 (18%); hepatobiliary disease, 25 (13%); Crohn disease, eight (4%); pancreatic disease, seven (4%); gynecologic disease, seven (4%); abdominal aortic aneurysm, seven (4%); bowel obstruction, five (3%); diverticulitis, five (3%); abscess, four (2%); pyelonephritis, three (2%); appendicitis, two (1%); ischemic bowel, one (1%); splenic disease, one (1%); and adrenal disease, one (1%). Forty (21%) patients with CT scans had other diagnoses. Of the 188 patients who underwent abdominal CT, 120 (64%) initially underwent radiography, whereas 68 (36%) underwent only CT. The distribution of hospital discharge diagnoses for patients examined with CT is illustrated in Table 2. Sensitivity, specificity, and accuracy of CT diagnoses were calculated and are illustrated in Table 4. CT had highest sensitivity for bowel obstruction (75%), urolithiasis (68%), and pancreatitis (60%). Specificities were between 91% and 100% for all CT diagnoses.

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Radiology Figure 4. Images obtained in a 43-year-old woman who had a history of abdominal surgery and presented with abdominal pain and vomiting. (a) Abdominal radiograph obtained with the patient supine demonstrates a nasogastric tube and no clinically important disease. (b) Transverse CT scan obtained with intravenously and orally administered contrast material shows multiple fluid-filled loops of small bowel consistent with small bowel obstruction. The diagnosis of small bowel obstruction from adhesions was confirmed at surgery.

Radiography and CT Cohort One hundred twenty (14%) of 871 patients underwent abdominal CT in the emergency department after abdominal radiography. Of these 120 patients, the diagnosis from the preceding abdominal radiographic examination was normal in 20% (24 of 120), nonspecific in 76% (91 of 120), and abnormal in 4% (five of 120). We compared abdominal radiography with CT for the following six diagnoses: bowel obstruction, urolithiasis, appendicitis, pyelonephritis, pancreatic disease, and diverticulitis. Sensitivity, specificity, and accuracy for each of six diagnoses are illustrated in Table 5. As compared with abdominal radiography, CT had a higher sensitivity for all six diagnoses. CIs are listed in Table 5. Examples of abdominal radiographs and CT scans for different diagnoses are demonstrated in Figures 1–5.

DISCUSSION Abdominal radiography has historically been the first imaging examination performed in the emergency department in evaluating abdominal pain. We found the diagnostic yield of abdominal radiography in patients in the emergency department to be low. This is in part because 68% of the interpretations were nonspecific and thus by definition could not be diagnostic. The most common interpretations in the nonspecific category 162

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TABLE 3 Sensitivity, Specificity, and Accuracy of Abdominal Radiography in 871 Patients Final Discharge Diagnosis Bowel obstruction Urolithiasis Appendicitis Pyelonephritis Pancreatitis Diverticulitis Intraabdominal foreign body

Sensitivity (%)

Specificity (%)

Accuracy (%)

49 (45, 52) 9 (7, 10) 0 (0, 23) 0 (0, 41) 0 (0, 8) 0 (0, 19)

98 (97, 99) 99 (99, 100) 100 (100, 100) 100 (100, 100) 100 (100, 100) 100 (100, 100)

96 84 98 99 95 98

90 (88, 92)

100 (100, 100)

100

Note.—Data in parentheses are the 95% CI.

TABLE 4 Sensitivity, Specificity, and Accuracy of Abdominal CT in 188 Patients Final Discharge Diagnosis

Sensitivity (%)

Specificity (%)

Accuracy (%)

Bowel obstruction Urolithiasis Appendicitis Pyelonephritis Pancreatitis Diverticulitis

75 (69, 81) 68 (61, 74) 50 (43, 57) 40 (33, 47) 60 (53, 67) 25 (19, 32)

99 (97, 100) 91 (87, 95) 100 (100, 100) 99 (98, 101) 98 (96, 100) 99 (97, 100)

98 88 99 98 97 94

Note.—Data in parentheses are the 95% CI.

were the various descriptions of bowel gas pattern other than normal, such as “nonspecific bowel gas pattern.” Seventy-one percent of the nonspecific category and 48% of all radiographic results had such an interpretation. Because of the ambiguity of

this phrase, we believe “nonspecific bowel gas pattern” should be abandoned, as has been advocated by others (15). The low diagnostic yield of abdominal radiography is due to its inherent low soft-tissue contrast and the fact that Ahn et al

TABLE 5 Comparison of Abdominal Radiography and Abdominal CT in 120 Patients Abdominal Radiography

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Final Diagnosis

Sensitivity (%)

Bowel obstruction (n ⫽ 3) 33 (25, 42) Urolithiasis (n ⫽ 25) 0 (0, 14) Appendicitis (n ⫽ 3) 0 (0, 71) Pyelonephritis (n ⫽ 2) 0 (0, 84) Pancreatitis (n ⫽ 3) 0 (0, 71) Diverticulitis (n ⫽ 9) 0 (0, 34)

Abdominal CT

Specificity (%)

Accuracy (%)

Sensitivity (%)

Specificity (%)

Accuracy (%)

100 (100, 100)

98

67 (58, 75)

99 (98, 101)

98

100 (96, 100)

80

68 (60, 76)

91 (85, 96)

86

100 (97, 100)

98

33 (25, 42)

100 (100, 100)

98

100 (97, 100)

98

50 (41, 59)

99 (98, 101)

98

100 (97, 100)

98

67 (58, 75)

99 (98, 101)

98

100 (97, 100)

93

33 (25, 42)

98 (96, 101)

93

Note.—Data in parentheses are the 95% CI.

Figure 5. Images obtained in a 49-year-old woman with right flank pain. (a) Abdominal radiograph demonstrates a 5-mm calcification in the right hemipelvis (arrowheads). The radiographic differential diagnosis included a phlebolith or a ureteral calculus. (b) Nonenhanced transverse CT scan through the pelvis demonstrates a distal right ureteral calculus (arrow).

many abdominal diseases do not have specific radiographic features. Causes of acute abdominal pain without specific radiographic manifestations include appendicitis, pyelonephritis, pancreatitis, and diverticulitis. Even for a diagnosis with a high sensitivity such as bowel obstruction (49%), half of the cases would be missed. Detection of intraabdominal foreign body was one exception we found in our study, as the sensitivity and specificity were 90% and 100%, respectively. Our results with the diagnostic yield of abdominal radiography are comparable with those of others (4,13,14) who reported diagnostic yields of 10%– 16%. The results with patients who underwent abdominal CT differed significantly from results in the abdominal radiography Volume 225

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cohort. CT had a higher sensitivity and similar specificity for multiple diagnoses including bowel obstruction, urolithiasis, appendicitis, pyelonephritis, pancreatitis, and diverticulitis. Others (7–12,16 –27) have corroborated these results; CT has been shown to be accurate in helping to diagnose bowel obstruction, inflammatory bowel disease, renal calculi, and appendicitis. In a study (16) of patients cared for nonsurgically in the emergency department, CT demonstrated a sensitivity of 90% for diagnosis of the cause of abdominal pain and provided information leading to a change in care in 27% of patients. In a separate study (17), the referring clinicians’ level of confidence in diagnosis was substantially improved and the hospital admission rate was reduced 24% after abdominal CT was performed in the emergency department. In the abdominal radiography and CT cohort (n ⫽ 120) in our study, CT (33%– 68%), as compared with abdominal radiography (0%– 33%), showed superior sensitivity for the six diagnosis types (Table 5). Although abdominal CT outperformed abdominal radiography as expected, sensitivities for appendicitis, urolithiasis, and bowel obstruction were lower than those reported (18 –27). In a prospective evaluation in 100 patients suspected of having appendicitis, helical CT evaluation of the abdomen with orally and rectally administered contrast material demonstrated sensitivity of 100%, specificity of 95%, and accuracy of 98% (18). In our study, CT sensitivity for appendicitis (50%) was markedly lower. We think that the low sensitivity for appendicitis in our study was due to two reasons. At the time of this study, we had

fewer CT referrals for patients suspected of having appendicitis, and our technique used transverse acquisition with 5–10-mm section thickness. Our current CT referrals for patients suspected of having appendicitis have increased, and our technique of 5-mm helical acquisition has increased our diagnostic yield. Likewise, the sensitivity for renal calculi was low in this study, most likely because of CT technique. In our series, we also found the specificity of abdominal radiography to be higher than expected. We can explain this finding with the relatively low number of true-positive cases in the six diagnoses we compared. Since specificity is defined as the number of patients who have normal examination results and do not have disease, small numbers of patients with the disease in question will inflate the specificity. Likewise, accuracy, defined as the number of true-positive and true-negative results divided by the total number of results, is high most likely because of the relatively low prevalence of disease. This study has limitations. It was a retrospective study, and the CT technique was limited as described. The board-certified radiologists interpreting both the abdominal radiographs and CT scans at our institution are approximately 40 years old on average and as such have had extensive training in cross-sectional imaging and perhaps less experience with conventional radiography. This could bias our study to CT, as the subtle findings on abdominal radiographs may have been detected by older radiologists with more extensive experience. A selection bias may be present given the unequal number of patients with ab-

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dominal radiographs and abdominal CT scans. This selection bias is related to the retrospective nature of our study and our sample recruitment methods. We examined patients who presented to the emergency department with abdominal pain rather than patients who already had a specific diagnosis. However, we believe that this is more applicable to the clinical practice of radiology in the emergency department setting. Lastly, we remind the reader of our small sample size for each diagnosis when comparing our results with those of previous studies. Despite these shortcomings, we believe the results are important because they affect patient care and can improve diagnostic yield in patients in the emergency department. Our study differs from those reported previously because it compares the diagnostic yield of radiography with that of CT in all patients presenting to the emergency department with abdominal pain, which reflects the clinical scenario faced by physicians in the emergency department. Our results suggest that abdominal radiography should not be used to screen all patients because of its low sensitivity for depicting common causes of abdominal pain. The possible exception to this suggestion is in patients in whom there is a high clinical index of suspicion of foreign body. Results of abdominal radiography were also not a predictor of who would undergo CT because the diagnosis at abdominal radiography was normal in 20% (24 of 120), nonspecific in 76% (91 of 120), and abnormal in 4% (five of 120) of patients who underwent abdominal radiography and subsequently CT. This finding suggests that clinical history was more important than the results of abdominal radiography in determining who would undergo CT. Our study results suggest that abdominal radiography has a low sensitivity in the examination of adult patients with abdominal pain in the emergency department setting; therefore, abdominal CT should be performed initially in patients with a high clinical index of suspicion of intraabdominal disease.

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