Korean J Radiol.  2016 Feb;17(1):39-46. 10.3348/kjr.2016.17.1.39.

Intra-Appendiceal Air at CT: Is It a Useful or a Confusing Sign for the Diagnosis of Acute Appendicitis?

• Hong HS
• Cho HS
• Woo JY
• Lee Y
• Yang I
• Hwang JY
• Kim HM
• Kim JW

• KMID: 2351161
• DOI: http://doi.org/10.3348/kjr.2016.17.1.39

Abstract

OBJECTIVE
To investigate the significance of intra-appendiceal air at CT for the evaluation of appendicitis.
MATERIALS AND METHODS
We retrospectively analyzed 458 patients (216 men, 242 women; age range, 18-91 years) who underwent CT for suspected appendicitis. Two independent readers reviewed the CT. Prevalence, amount, and appearance of intra-appendiceal air were assessed and compared between the patients with and without appendicitis. Performance of CT diagnosis was evaluated in two reading strategies: once ignoring appendiceal air (strategy 1), and the other time considering presence of appendiceal air as indicative of no appendicitis in otherwise indeterminate cases (strategy 2), using receiver operating characteristic (ROC) analysis.
RESULTS
Of the 458 patients, 102 had confirmed appendicitis. The prevalence of intra-appendiceal air was significantly different between patients with (13.2%) and without (79.8%) appendicitis (p < 0.001). The amount of appendiceal air was significantly lesser in patients having appendicitis as compared with the normal group, for both reader 1 (p = 0.011) and reader 2 (p = 0.002). Stool-like appearance and air-fluid levels were more common in the appendicitis group than in the normal appendix for both readers (p < 0.05). Areas under the ROC curves were not significantly different between strategies 1 and 2 in reader 1 (0.971 vs. 0.985, respectively; p = 0.056), but showed a small difference in reader 2 (0.969 vs. 0.986, respectively; p = 0.042).
CONCLUSION
Although significant differences were seen in the prevalence, amount, and appearance of intra-appendiceal air between patients with and without appendicitis, it has a limited incremental value for the diagnosis of acute appendicitis.

Keyword

Acute appendicitis; Intra-appendiceal air; CT diagnosis

MeSH Terms

Acute Disease
Adolescent
Adult
Aged
Aged, 80 and over
Appendicitis/pathology/*radiography
Appendix/pathology/*radiography
Female
Humans
Male
Middle Aged
Prevalence
ROC Curve
Retrospective Studies
Tomography, X-Ray Computed
Young Adult

Figure

• 

  Fig. 1 53-year-old female patient presented to emergency department with right-sided abdominal pain. A, B. Hemorrhagic cyst was found in right adnexa (not shown). Contrast-enhanced transverse (A) and coronal (B) CT images demonstrate normal appendix (arrows in A and B) containing intraluminal air, with appearance of scattered air bubbles and columns.

• 

  Fig. 2 49-year-old male patient diagnosed as acute appendicitis by surgery. A, B. Contrast-enhanced transverse (A) and coronal (B) CT images show characteristic findings of acute appendicitis, including appendiceal enlargement, appendiceal wall thickening and enhancement, and periappendiceal fat stranding. Appendix (arrows in A and B) is abnormally enlarged and dilated with air-fluid level in lumen (arrowhead in A).

Reference

1. Rao PM, Rhea JT, Novelline RA, Mostafavi AA, McCabe CJ. Effect of computed tomography of the appendix on treatment of patients and use of hospital resources. N Engl J Med. 1998; 338:141–146.

2. Jacobs JE, Balthazar EJ. Diseases of the appendix. In : Gore RM, Levine MS, editors. Textbook of gastrointestinal radiology. 3rd ed. Philadelphia, PA: Saunders;2008. p. 1039–1069.

3. Pickhardt PJ, Lawrence EM, Pooler BD, Bruce RJ. Diagnostic performance of multidetector computed tomography for suspected acute appendicitis. Ann Intern Med. 2011; 154:789–796. W-291

4. Birnbaum BA, Wilson SR. Appendicitis at the millennium. Radiology. 2000; 215:337–348.

5. Pinto Leite N, Pereira JM, Cunha R, Pinto P, Sirlin C. CT evaluation of appendicitis and its complications: imaging techniques and key diagnostic findings. AJR Am J Roentgenol. 2005; 185:406–417.

6. van Randen A, Laméris W, van Es HW, ten Hove W, Bouma WH, van Leeuwen MS, et al. Profiles of US and CT imaging features with a high probability of appendicitis. Eur Radiol. 2010; 20:1657–1666.

7. Choi D, Park H, Lee YR, Kook SH, Kim SK, Kwag HJ, et al. The most useful findings for diagnosing acute appendicitis on contrast-enhanced helical CT. Acta Radiol. 2003; 44:574–582.

8. Bixby SD, Lucey BC, Soto JA, Theysohn JM, Ozonoff A, Varghese JC. Perforated versus nonperforated acute appendicitis: accuracy of multidetector CT detection. Radiology. 2006; 241:780–786.

9. Callahan MJ, Rodriguez DP, Taylor GA. CT of appendicitis in children. Radiology. 2002; 224:325–332.

10. Rettenbacher T, Hollerweger A, Macheiner P, Rettenbacher L, Frass R, Schneider B, et al. Presence or absence of gas in the appendix: additional criteria to rule out or confirm acute appendicitis--evaluation with US. Radiology. 2000; 214:183–187.

11. Tamburrini S, Brunetti A, Brown M, Sirlin CB, Casola G. CT appearance of the normal appendix in adults. Eur Radiol. 2005; 15:2096–2103.

12. Webb EM, Wang ZJ, Coakley FV, Poder L, Westphalen AC, Yeh BM. The equivocal appendix at CT: prevalence in a control population. Emerg Radiol. 2010; 17:57–61.

13. Kim HC, Yang DM, Kim SW, Park SJ. Reassessment of CT images to improve diagnostic accuracy in patients with suspected acute appendicitis and an equivocal preoperative CT interpretation. Eur Radiol. 2012; 22:1178–1185.

14. Azok JT, Kim DH, Munoz Del Rio A, Sonavane SK, Bhalla S, Anaya-Baez V, et al. Intraluminal air within an obstructed appendix: a CT sign of perforated or necrotic appendicitis. Acad Radiol. 2012; 19:1175–1180.

15. Kim K, Kim YH, Kim SY, Kim S, Lee YJ, Kim KP, et al. Low-dose abdominal CT for evaluating suspected appendicitis. N Engl J Med. 2012; 366:1596–1605.

16. Cohen J. Weighted kappa: nominal scale agreement with provision for scaled disagreement or partial credit. Psychol Bull. 1968; 70:213–220.

17. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics. 1977; 33:159–174.

18. Rao PM, Rhea JT, Novelline RA. Appendiceal and peri-appendiceal air at CT: prevalence, appearance and clinical significance. Clin Radiol. 1997; 52:750–754.

19. Clarke PD. Computed tomography of gangrenous appendicitis. J Comput Assist Tomogr. 1987; 11:1081–1082.

20. Killen DA, Brooks DW Jr. Gas-filled appendix: a roentgenographic sign of acute appendicitis. Ann Surg. 1965; 161:474–478.

21. Rao PM, Rhea JT, Novelline RA. Distal appendicitis: CT appearance and diagnosis. Radiology. 1997; 204:709–712.

22. Cabarrus M, Sun YL, Courtier JL, Stengel JW, Coakley FV, Webb EM. The prevalence and patterns of intraluminal air in acute appendicitis at CT. Emerg Radiol. 2013; 20:51–56.

23. Rao PM. Technical and interpretative pitfalls of appendiceal CT imaging. AJR Am J Roentgenol. 1998; 171:419–425.

24. Levine CD, Aizenstein O, Wachsberg RH. Pitfalls in the CT diagnosis of appendicitis. Br J Radiol. 2004; 77:792–799.

25. Kim SY, Lee KH, Kim K, Kim TY, Lee HS, Hwang SS, et al. Acute appendicitis in young adults: low-versus standard-radiation-dose contrast-enhanced abdominal CT for diagnosis. Radiology. 2011; 260:437–445.

26. Ganguli S, Raptopoulos V, Komlos F, Siewert B, Kruskal JB. Right lower quadrant pain: value of the nonvisualized appendix in patients at multidetector CT. Radiology. 2006; 241:175–180.