Rationale and Objectives
To propose a useful computed tomography (CT) criterion, the diameter with compression (DWC), especially in appendices with borderline diameters.
Materials and Methods
We retrospectively collected 216 patients with visible appendices on CT after clinicopathologic confirmation of appendicitis. Each CT criterion of appendicitis was evaluated by an experienced abdominal radiologist: maximal outer diameter (MOD), DWC, mural thickness and enhancement, periappendiceal infiltration, and appendicolith. DWC is the expected diameter after deduction of the intraluminal compressible contents such as air and feces. All the CT criteria were compared in the appendicitis and nonappendicitis group.
Results
The areas under the receiver operating characteristic curve (AUC) of the MOD and the DWC were 0.967 and 0.973, respectively. The optimal cutoff value was 8.2 mm for the MOD and 6.6 mm for the DWC. Twenty-five of the 80 appendicitis patients (31.2%) and 62 of the 136 nonappendicitis patients (45.6%) had MODs between 5.7 mm and 9.8 mm in the overlap between the two groups. In this overlap, the AUC of the MODs declined sharply to 0.767, whereas the AUC of the DWCs remained 0.923. Use of the criterion of DWC >6.6 mm yielded a sensitivity of 84.0%, a specificity of 88.7%, and an accuracy of 87.4%. There were no other criteria with both sensitivity and specificity >80% in the range of overlap.
Conclusions
The proposed CT criterion of the DWC is not affected by normal distension or periappendiceal inflammation but only by true appendicitis. Therefore, DWC can improve the diagnostic performance of appendicitis regardless of the MOD.
Making a diagnosis of acute appendicitis begins with history taking and physical examination by clinicians and is completed by computed tomography (CT) and ultrasonography (US) in >50% of patients . US and CT are complementary approaches. US was the first diagnostic imaging modality for right lower quadrant pain until the early 2000s because it requires neither radiation nor an intravenous contrast medium . Use of CT has increased in the last decade as multidetector row computed tomography (MDCT) scanners have become more common, because these can provide rapid and accurate information not only on the appendix but also on other organs . US has a limited ability to locate the appendix, while incorrect diagnoses occur in CT examinations . Diagnostic errors in CT interpretation happen in two different circumstances depending on the visibility of the appendix. Visibility can be improved by optimization of CT scanning protocols and application of three-dimensional techniques or simply by using US . This is because the main problems are patients’ paucity of intra-abdominal fat or abnormal locations of the appendix . Diagnostic difficulties in cases of visible appendices arise from indeterminate CT findings especially in appendices with borderline diameters . Some important CT criteria for appendicitis are the same as the US criteria ; however, simple extrapolation from US to CT may not be valid because CT images are obtained without compression . For this and other reasons, several studies have compared the MODs of appendices on CT in patients with appendicitis to those of healthy people. A normal appendix is defined as <10 mm in diameter in most publications . On the basis of these results, an appendix with an MOD of 6–10 mm is indeterminate. Several groups have tried to improve the diagnostic performance for appendices with borderline MOD by proposing new CT criteria or combining established CT criteria . However, there are no published reports investigating diagnostic performance by established CT criteria for appendices with borderline MOD from the perspective of appendiceal compressibility, as in the case of the US criteria.
Hence, we investigate the diagnostic performance of established CT criteria in appendices with borderline MOD. We propose a possible new criterion to take account of appendiceal enlargement not because of appendicitis, namely diameter with compression (DWC), derived from the US criteria.
Materials and methods
Patients
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CT Scan Protocol
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Interpretation of CT Studies
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Statistical Analysis
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Results
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Table 1
Sensitivity, Specificity, and Accuracy of Established Criteria
Criterion Sensitivity (%) Specificity (%) Accuracy (%) All ∗ Overlap † All ∗ Overlap † All ∗ Overlap † Maximal outer diameter > 8.2 mm 88.8 (71/80) 64.0 (16/25) 93.4 (127/136) 83.9 (52/62) 91.7 (198/216) 78.2 (68/87) Maximal outer diameter > 6 mm 97.5 (78/80) 92.0 (23/25) 59.6 (81/136) 11.3 (7/62) 73.6 (159/216) 34.5 (30/87) Diameter with compression > 6.6 mm 93.8 (75/80) 84.0 (21/25) 94.9 (129/136) 88.7 (55/62) 94.4 (204/216) 87.4 (76/87) Mural thickness > 1.1 mm 87.5 (70/80) 88.0 (22/25) 41.2 (56/136) 30.6 (19/62) 58.3 (126/216) 47.1 (41/87) Mural thickness > 3 mm 78.8 (63/80) 16.0 (21/25) 8.8 (12/136) 80.6 (50/62) 34.7 (75/216) 62.1 (54/87) Presence of mural enhancement 96.3 (77/80) 100 (25/25) 80.9 (110/136) 69.4 (43/62) 86.6 (187/216) 78.2 (68/87) Presence of periappendiceal infiltration 85.0 (68/80) 80.0 (20/25) 73.5 (100/136) 66.1 (41/62) 77.8 (168/216) 70.1 (61/87) Presence of appendicoliths 32.5 (26/80) 16.0 (4/25) 97.8 (133/136) 96.8 (60/62) 73.6 (159/216) 73.6 (64/87)
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Discussion
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