title: Computed tomography evaluation of the normal appendix: comparison of low-dose and standard-dose unenhanced helical computed tomography.
abstract: OBJECTIVE
  To determine the visualization rate of the normal appendix on low- and standard-dose unenhanced computed tomography (CT) and to evaluate the variables that may influence the identification of the appendix.
  
  
  METHODS
  The study population was derived from the previous study, approved by the internal review board, investigating the effectiveness of low-dose CT (LDCT) in diagnosis of urolithiasis. Sixty-eight patients presenting with acute flank pain underwent 2 unenhanced dual-slice CT examinations. Standard-dose CT (SDCT) scans were obtained using 2 x 5-mm collimation, 120 kVp, and 170 effective mAs and followed by LDCT using 30 or 50 effective mAs. Two independent board-certified radiologists retrospectively recorded the visualization, outer diameter, and the wall thickness of normal appendices. The diameters, circumference, and cross-sectional area of the abdomen were measured.
  
  
  RESULTS
  The prevalence of appendectomy was 8.8% (6 of 68 patients). The means of the 2 reviewers' sensitivity, specificity, positive and negative predictive values, and accuracy for visualization of normal appendix at SDCT versus LDCT respectively were 78% versus 73%, 100% versus 92%, 100% versus 99%, 31% versus 24%, and 80% versus 74% (P = 0.39-0.75). The interobserver agreement was good at both SDCT (kappa = 0.61) and LDCT (kappa = 0.74). Overall 40% to 58% of appendices at LDCT and 33% to 47% at SDCT was larger than 6 mm. There was no significant correlation in the appendix visualization neither with abdominal dimensions nor with visceral or pericecal fat at both dose sets. The calculated mean effective radiation dose at LDCT was 70% to 82% less than SDCT.
  
  
  CONCLUSIONS
  Low- and standard-dose nonenhanced helical CT can visualize a normal appendix with high accuracy and good interobserver agreement. The diameter of normal appendix overlaps with that of appendicitis at CT. A diameter of 10.0 mm should be considered as the upper limit of normal in the absence of any other CT signs of appendicitis.
authors: Department of Radiology, School of Medicine, Pamukkale University, Kinikli, Denizli, Turkey. nkarabulut@yahoo.com
authors: Nevzat
authors: N
authors: Karabulut
authors: Nurefsan
authors: N
authors: Boyaci
authors: Baki
authors: B
authors: Yagci
authors: Duygu
authors: D
authors: Herek
authors: Yilmaz
authors: Y
authors: Kiroglu
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001065:Appendix / Q000000981:diagnostic imaging*; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011829:Radiation Dosage; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D036542:Tomography, Spiral Computed / Q000379:methods*; D052878:Urolithiasis / Q000000981:diagnostic imaging