Rationale and Objectives
To assess computed tomographic (CT) signs that have been described in published studies for the diagnosis of appendicitis to identify independent findings that predict appendicitis.
Methods and Materials
A retrospective database search identified 67 patients with a CT scan of the abdomen/pelvis and pathologic evaluation of the appendix, including 41 with appendicitis and 26 with a normal appendix on pathologic examination. Each computed tomogram was re-evaluated by three independent, blinded observers who evaluated appendix diameter, enhancement of the appendix, thickening of the appendix, presence of an appendicolith, infiltration of peri-appendiceal fat, focal cecal thickening, local lymphadenopathy, fluid collections, non-appendiceal bowel thickening, non-periappendiceal infiltration of fat, and comparison of peri-appendiceal fat infiltration to thickening of adjacent bowel loops.
Results
Mean diameter of the normal appendix (6.7 ± 2.2 mm) was significantly lower than that of the inflamed appendix (12.1 ± 4.3 mm; P < .001). Significant univariate predictors of appendicitis included appendix diameter >8 mm (odds ratio [OR] 34.8), enhancement of the appendix (OR 4.4), thickening of the appendix (OR 4.3), infiltration of peri-appendiceal fat (OR 5.5), focal cecal thickening (OR 5.1), non-appendiceal bowel thickening (OR 0.4), and non-periappendiceal infiltration of fat (OR = 0.3). Of these variables, only appendix diameter and enhancement of the appendix were significant independent predictors of appendicitis on multivariate analysis. An overall diagnostic impression based on all secondary signs was less accurate than a diagnosis based on appendix diameter alone (receiver-operating characteristic analysis: Az = 0.80 vs. Az = 0.91, P = .02). Sensitivity/specificity of appendix diameter was 84%/87% using a cutoff between 8 and 9 mm and 97%/48% using a cutoff between 6 and 7 mm.
Conclusion
Appendix diameter is the best single diagnostic criterion for appendicitis on CT scan. A cutoff between 8 and 9 mm provided the best balance of sensitivity/specificity in our study population, whereas a cutoff between 6 and 7 mm improved sensitivity at the expense of specificity. The presence of appendiceal enhancement provided additional diagnostic information, but other secondary signs of appendicitis did not improve diagnostic accuracy.
Appendicitis is the most commonly encountered cause of abdominal pain requiring surgical management ( ). Delayed or inaccurate diagnosis of appendicitis can lead to significant morbidity and mortality. Within the United States, there are a reported one million hospital days per year from 250,000 cases annually of appendicitis ( ). The incidence of appendicitis is greatest in the second decade of life ( ).
Computed tomography has been advocated as a cost-efficient and accurate way to diagnose appendicitis, particularly in the setting of an inconclusive clinical examination ( ). In many hospitals, computed tomography is considered the standard of care for the evaluation of suspected appendicitis (7). Computed tomographic (CT) findings described in published studies that suggest a diagnosis of appendicitis include the presence of an enlarged appendix measuring larger than 6 mm in diameter, appendiceal wall thickening, peri-appendiceal fat stranding, the presence of an appendicolith, and appendiceal wall enhancement ( ). Other CT signs of appendicitis are adjacent bowel wall thickening, cecal apical thickening, the “cecal bar” or arrowhead sign, adjacent fat stranding, the presence of an abscess, and lymphadenopathy ( ). In 13% of cases performed for the evaluation of acute appendicitis, the appendix is not visualized, and secondary findings related to appendicitis are used for the diagnosis ( ).
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Materials and methods
Database Search
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CT Scan Protocol
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Scan Interpretation
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Table 1
Study Form Completed for Each Subject
•Appendix visualized Y N •Appendix diameter (outer to outer wall) ______ mm •Appendicolith Y N •Appendiceal wall enhancement Y N •Appendiceal wall thickening Y N •Peri-appendiceal fat stranding None mild moderate severe •Fat stranding not at appendix Y N •Non-appendiceal bowel wall thickening Y N •Fat stranding: bowel wall thickening None/equal/mildly greater/moderately greater/markedly greater •Focal cecal apical thickening Y N •Right lower quadrant lymphadenopathy None Normal size Enlarged •Peri-appendiceal or adjacent abscess Y N •Overall suspicion for appendicitis None/probably not/probably is/definite
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Statistical Analysis
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Univariate analysis
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Multivariate analysis
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Receiver-operating characteristic analysis
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Interobserver Agreement
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Results
Study Population Demographics
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Pathology
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Visualization of Appendix
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Univariate Analysis
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Multivariate Analysis
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Appendix Diameter
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Overall Impression
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Table 2
Univariate Analysis
Observation #1 #2 #3 Overall OR_P_ Value AP diameter 49.5 53.2 18.8 34.8 <.001 AP stone 0.82 10.0 2.7 1.1 .81 AP enhancement 6.9 2.7 5.2 4.4 .001 Arrow sign 4.0 1.3 17 5.1 .002 AP wall thickening 6.7 4.3 3.1 4.3 <.001 Peri-AP stranding 4.4 9.7 3.7 5.5 .001 Other fat stranding 0.34 0.13 0.28 0.30 .008 Other wall thickening 0.41 0.56 0.28 0.40 .07 Peri-AP stranding vs. other wall thickening (5 patients) 0.65 1.41 1.58 1.2 .36 Lymphadenopathy (3 patients) 0.95 1.27 2.02 1.2 .44 Abscess 0.88 0.40 0.31 0.57 .35 Overall impression 18.0 14.1 31.5 18.2 <.001 AP, anteroposterior; OR, odds ratio.
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Cases with Diameter <9 mm
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Cases with Nonvisualized Appendix
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Interobserver Agreement
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Discussion
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