title: Appendiceal diameter: CT versus sonographic measurements.
abstract: BACKGROUND
  Ultrasound and CT are the dominant imaging modalities for assessment of suspected pediatric appendicitis, and the most commonly applied diagnostic criterion for both modalities is appendiceal diameter. The classically described cut-off diameter for the diagnosis of appendicitis is 6 mm when using either imaging modality.
  
  
  OBJECTIVE
  To demonstrate the fallacy of using the same cut-off diameter for both CT and US in the diagnosis of appendicitis.
  
  
  METHODS
  We conducted a retrospective review of patients younger than 18 years who underwent both US and CT of the appendix within 24 h. The shortest transverse dimension of the appendix was measured at the level of the proximal, mid and distal appendix on US and CT images. We compared mean absolute difference in appendiceal diameter between US and CT, using the paired t-test.
  
  
  RESULTS
  We reviewed exams of 155 children (58.7% female) with a mean age of 11.3 ± 4.2 years; 38 of the children (24.5%) were diagnosed with appendicitis. The average time interval between US and CT was 7.0 ± 5.4 h. Mean appendiceal diameter measured by CT was significantly larger than that measured by US in cases without appendicitis (5.3 ± 1.0 mm vs. 4.7 ± 1.1 mm, P < 0.0001) and in cases with appendicitis (8.3 ± 2.2 mm vs. 7.0 ± 2.0 mm, P < 0.0001). Mean absolute diameter difference at any location along the appendix was 1.3-1.4 mm in normal appendices and 2 mm in cases of appendicitis.
  
  
  CONCLUSIONS
  Measured appendiceal diameter differs between US and CT by 1-2 mm, calling into question use of the same diameter cut-off (6 mm) for both modalities for the diagnosis of appendicitis.
authors.affiliation: Department of Radiology, University of Cincinnati Medical Center, Cincinnati, OH, USA.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Orscheln
authors.affiliation: Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229, USA. andrew.trout@cchmc.org.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Trout
mesh_terms: D000328:Adult; D001064:Appendicitis / Q000000981:diagnostic imaging* / Q000473:pathology*; D001065:Appendix / Q000000981:diagnostic imaging* / Q000473:pathology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D009929:Organ Size; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014463:Ultrasonography / Q000379:methods*
keywords: Appendicitis; Appendix; Children; Computed tomography; Diameter; Ultrasound