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Gastrointestinal Imaging |
1 Department of Radiology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78284-7800.
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: Fifty-eight CT scans in cases of proved diverticulitis (n = 27) or colon cancer (n = 31) were evaluated retrospectively by radiologists (blinded to the proved diagnosis) for the presence or absence of previously reported CT findings. These findings were correlated with the pathologic or final clinical diagnosis. The retrospective findings were applied in a prospective evaluation with a new set of 72 CT scans. The same five radiologists rendered a diagnosis according to a five-point confidence scale from definitely benign to definitely malignant. Individual and consensus readings were correlated with the final diagnosis.
RESULTS: Retrospectively, pericolonic inflammation (P < .01) and segment involvement greater than 10 cm (P < .012) were the most significant findings for diverticulitis; pericolonic lymph nodes (P < .0001) and luminal mass (P < .003) were the most significant findings for colon cancer. Prospectively, an unequivocal diagnosis was made correctly in 16 (40%) of 40 cases of diverticulitis and 21 (66%) of 32 cases of colon cancer.
CONCLUSION: When there are no pericolonic lymph nodes adjacent to a segment of colonic wall thickening, with pericolonic inflammatory changes, the most likely diagnosis is diverticulitis. When pericolonic lymph nodes are present, with or without pericolonic edema, the most likely diagnosis is colon cancer.
Index terms: Colon, diverticula, 75.273 • Colon, neoplasms, 75.321 • Computed tomography (CT), helical 75.12115, 75.12143
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Analysis of CT Findings in the Retrospective Component
From our radiology database, 58 CT scans from 57 patients (27 cases of diverticulitis and 31 cases of colon cancer) were identified for inclusion in the study. There were 40 men and 17 women aged 17–71 years (mean age, 57 years). One patient with cancer in the sigmoid colon also had a metachronous cancer in the descending colon and therefore had two CT scans that were included in the study. In 27 of the 30 patients with colon cancer, the final diagnosis was reached by means of surgery or colonoscopy. The remaining three cases of colon cancer were diagnosed with biopsy of liver metastases. In 23 of the 27 patients with diverticulitis, the diagnosis was confirmed with surgery or colonoscopy. The remaining four cases of diverticulitis were diagnosed with clinical follow-up. CT examinations were performed with a variety of CT scanners (HiSpeed Advantage, GE Medical Systems, Milwaukee, Wis; PQ Helical, Picker International, Highland Heights, Ohio; Tomoscan TX-60, Phillips Medical Systems, Shelton, Conn; and model DR-3, Siemens, Erlangen, Germany). All patients had received oral contrast material (1,000 mL of 2%–4% meglumine and sodium diatrizoate [Gastrografin, Bracco Diagnostics, Princeton, NJ or MD-Gastroview, Mallinckrodt, St Louis, Mo]) 2–2
hours before the CT study, and 49 patients (85%) received 400–500 mL of 2%–4% rectal contrast material (meglumine and sodium diatrizoate). Scanning was performed in the craniocaudal direction, beginning at the dome of the right hemidiaphragm, 40–70 seconds after the administration of 125–150 mL of ionic or nonionic iodinated contrast medium (350 mg/mL iohexol [Omnipaque; Nycomed, Princeton, NJ], ioversol [Optiray 320; Mallinckrodt], or iothalamate meglumine [Conray 60; Mallinckrodt]), injected at rates varying between 2 and 3 mL/sec. Scanners were collimated to 8–10 mm, with contiguous scans obtained down to the symphysis pubis. The CT images depicting a colonic abnormality were selected for evaluation. The names and identification markers on the images were masked. The selected CT images were grouped together in a random fashion. The images were then evaluated individually by five board-certified radiologists (K.N.C., S.C., A.A.G., C.C.E., G.D.D.) (blinded to the proved diagnosis) for published (1,2,3–6) CT findings of diverticulitis and colon cancer. These included length of segment involved, pericolonic inflammation, pericolonic edema, luminal mass, pericolonic lymph nodes, and extraluminal fluid or air (Fig 1).
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Each radiologist was asked to identify the presence or absence of the CT findings in each case. Results were recorded on standardized worksheets. The majority opinion in each case was tabulated. The data thus obtained were correlated with the proved diagnoses. The prevalence of all CT findings was calculated in each of the two conditions. The statistical significance was calculated by using the Fisher exact test. The most useful signs for differentiating between diverticulitis and colon cancer were thus identified (Table 1). After the statistical tests were performed, all cases were reviewed jointly by the five readers as an educational exercise to maximize performance on the prospective portion of the study. At the time of the joint image review, additional findings not included in the individual readings were identified and discussed. These included shoulder formation, eccentric wall thickening, and fluid at the root of the mesentery. On the basis of the perceived potential diagnostic value, it was decided to include these findings in the prospective study. Shoulder formation was considered to be present when there was a soft-tissue mass in the wall similar to the apple core lesion described on contrast (barium or meglumine and sodium diatrizoate) enema studies. Wall thickening was considered to be eccentric when there was asymmetry in the thickening of the two walls of the colon. Whenever thickening or fluid in the root of the sigmoid mesentery was seen, it was recorded.
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Each reader identified the CT signs present and rendered a diagnosis in each case. The evaluated signs included those of the retrospective study and the three additional signs identified in the joint review. Each reader indicated his or her confidence in each case by marking a five-point confidence scale: 1, definitely diverticulitis; 2, probably diverticulitis; 3, indeterminate; 4, probably malignant; and 5, definitely malignant. The final diagnoses in these patients were then identified.
The data were analyzed in two ways. The individual CT diagnoses were correlated with the final diagnosis in each case (Table 2). There were thus a total of 360 CT readings (five readers x 72 studies) that were used to determine the overlap in each of the five confidence categories. Additionally, the majority (three or more readers) CT diagnosis in each patient was determined from the diagnoses rendered by the individual readers. This was then correlated against the final diagnosis in each patient. The majority opinion was also tabulated for individual findings evaluated in each case.
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was used for interobserver agreement. Receiver operating characteristic (ROC) curves were also drawn for individual readers and for the group. Multivariate logistic regression was used to determine the combination of CT findings for which the accuracy of diagnosis was the highest. |
RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Applying the statistical analysis, the most specific findings for diverticulitis were presence of pericolonic inflammation (P < .01) and length of segment longer than 10 cm (P < .012). The most specific findings for colon cancer were presence of lymph nodes (P < .001) and luminal mass (P < .01). Pericolonic edema (P = .10) favored diverticulitis, but the numbers were not large enough to attain statistical significance (Table 1).
Application of CT Findings in the Prospective Component
There were 40 cases of diverticulitis and 32 cases of colon cancer. Diverticulitis involved the sigmoid colon in 34 cases, descending colon in four, and transverse colon in two. Colon cancer involved the sigmoid in 23 cases, descending colon in two, transverse colon in two, and ascending colon in five. When all individual readings were taken into consideration, there were 360 readings (72 x 5 = 360). The correlation of these readings with the final diagnosis is shown in Table 2. There were 83 readings of definite diverticulitis. Of these, 80 (96%) were cases of diverticulitis and three (4%) were cases of colon cancer. All three readings of colon cancer in the definitely benign category were by a single reader. There were 96 readings of definite colon cancer. Of these, 92 (96%) were cases of colon cancer and four readings were cases of diverticulitis. Thus, for the individual readings, the accuracy of CT in making a correct unequivocal diagnosis of diverticulitis or colon cancer was 96%. However, an unequivocal diagnosis could be made in only 49% of all cases, whereas in the remaining 51%, there was overlap in the CT appearances of the two entities.
The correlation of majority CT diagnoses with the final diagnoses is also shown in Table 2. Sixteen cases were read as definite diverticulitis and all had diverticulitis. Eighteen cases were read as probable diverticulitis; of these, 16 had diverticulitis and two had colon cancer. Eleven cases were read as indeterminate; of these, seven (64%) had diverticulitis and four (36%) had colon cancer. Six cases were read as probable colon cancer; of these, one (17%) had diverticulitis and five (83%) had colon cancer. Twenty-one cases were called definite colon cancer. All of these had colon cancer. From the above, an unequivocal and correct diagnosis of diverticulitis or colon cancer was rendered in 37 (51%) of 72 cases. In the remaining 35 cases (49%), there was enough overlap in the findings to make the CT diagnosis equivocal. Representative cases are illustrated in Figures 2–7.
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) of 95.6%. The area under ROC curves for the group and the five individual readers was 96% and 87%–98%, respectively (Fig 8).
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Analysis of the frequency of the associated CT findings showed that, in diverticulitis, pericolonic inflammation or length of involvement of greater than 10 cm yielded a sensitivity of 95%, while fluid at the root of the mesentery or extraluminal air or fluid yielded a specificity of 90% and 94%, respectively (Table 3). However, the accuracy for diverticulitis was highest for pericolonic inflammation and fluid at the root of the mesentery (68%).
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Multivariate analysis with use of logistic regression was performed. The predictors that significantly enhanced the diagnostic capability of presence or absence of lymph nodes are pericolonic inflammation (P < .0015) and edema (P < .0095). When the lymph nodes were absent and inflammation and/or edema was present, the sensitivity was 92% and accuracy was 86% for diagnosis of diverticulitis. When lymph nodes were present with or without pericolonic edema, the sensitivity was 90% and accuracy 79% for colon cancer. Specificity and accuracy for colon cancer were improved when pericolonic inflammation was absent in addition to the other two findings. The results are shown in Table 3.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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From our retrospective review, we found that for the diagnosis of diverticulitis, the most specific findings were pericolonic stranding and length of the involved segment of more than 10 cm. The presence of pericolonic edema favored diverticulitis but did not attain statistical significance. For colon cancer, the most specific findings were the presence of pericolonic lymph nodes and luminal mass. On analyzing our data from the prospective evaluation, the statistical significance for luminal mass for colon cancer and stranding for diverticulitis was even stronger (luminal mass, P < .0002; stranding, P < .0005). The P values for the presence of pericolonic lymph nodes (P < .0001) and shoulder formation (P < .0001) for colon cancer were highly significant. Despite statistically significant data, however, we found that an overlap of the findings allowed an unequivocal diagnosis in only 16 (40%) of 40 cases of diverticulitis and 21 (66%) of 32 cases of colon cancer. According to the majority (three or more readers) opinion, there was no case of cancer in the "definite diverticulitis" group and no case of diverticulitis in the "definite colon cancer" group, thus yielding an accuracy of 100%. In all other categories (2–4), however, there was an overlap in the two diseases. Analysis of the individual interpretations showed that there were a few interpretive mistakes in the definitely benign or malignant categories. Three cases of colon cancers were called definitely benign and four cases of diverticulitis were called definitely malignant. It is interesting to note that all three colon cancers were missed by one junior faculty in our group. However, ROC curves were similar for each of the five readers, and the diagnosis for the group showed good interobserver agreement (Cronbach coefficient = 95.6%). Thus, there was no marked difference in the abilities of the five different readers.
Our data show that there is a significant overlap in the CT appearance of colon cancer and diverticulitis. The degree of overlap in our study is much higher than the 10% previously reported by Balthazar et al (1). However, their study was nonblinded, with the cases merely deemed atypical by the readers. The high degree of overlap between diverticulitis and colon cancer detected in our study can be explained on the basis of the low sensitivity of the CT findings. Fluid at the root of the mesentery and extraluminal air or fluid had sensitivities for diverticulitis of 50% and 30%, respectively. Similarly, luminal mass, shoulder formation, and lymph nodes had sensitivities for colon cancer of 47%, 50%, and 63%, respectively. Thus, the number of cases in which these findings were present were few. When these findings were present, however, the specificity and accuracy of diagnosis were very high. Multivariate logistic regression showed that the presence of the findings of one disease in the absence of the findings of the other had an even higher specificity and added to the confidence of diagnosis. When pericolonic lymph nodes were absent and inflammation and/or edema were present, the specificity for diverticulitis was 90%. When lymph nodes were present and/or no edema and no inflammation were present, the specificity for colon cancer was 92%.
The implications of the above findings become clear by looking at the aim of imaging in the context of differentiating between diverticulitis and colon cancer. Imaging is performed to rule out colon cancer in a patient with symptoms of diverticulitis. In this, CT has a low accuracy, with unequivocal diagnosis possible only in 49% of cases. The remaining 51% must undergo colonoscopy or follow-up imaging to clarify the diagnosis. In the context of ruling out cancer, however, it is important that a diagnosis of benign disease have high accuracy. The specificity of the CT findings of diverticulitis and colon cancer is so high that, depending on the reader's experience, an unequivocal diagnosis carries an accuracy of 100% for both diverticulitis and colon cancer; in such patients, no further diagnostic work-up is required. However, further evaluation may be necessary to plan for surgery.
In conclusion, we found statistically significant differences in the frequency of different CT findings in patients with colon cancer and those with diverticulitis. Although there is good statistical correlation, there was considerable overlap (51%) in the CT diagnosis of these two conditions. By using strict criteria, however, one can make a correct unequivocal diagnosis of diverticulitis or cancer in approximately 50% of cases. In those cases, the patients need not undergo further diagnostic evaluation, and further evaluation may be done for surgical planning. When there are no pericolonic lymph nodes adjacent to a segment of colonic thickening, with pericolonic inflammatory changes, diverticulitis is the most likely diagnosis. When there are pericolonic lymph nodes adjacent to a segment of colonic thickening, colon cancer is the most likely diagnosis.
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Footnotes |
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From the 1996 RSNA scientific assembly.
Abbreviation: ROC = receiver operating characteristic
Author contributions: Guarantors of integrity of entire study, all authors; study concepts and design, all authors; definition of intellectual content, all authors; literature research, K.N.C., S.C.; clinical studies, all authors; data acquisition, K.N.C., S.F.F.; data analysis, all authors; statistical analysis, K.N.C., S.C., G.D.D.; manuscript preparation, K.N.C., S.C.; manuscript editing, K.N.C., S.C., C.C.E., G.D.D.; manuscript review, all authors.
Received February 25, 1998;
revision requested May 4, 1998; revision received May 27, 1998;
accepted August 10, 1998.
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References |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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