To the Editor:
We read the article by Rao et al 1 about the “introduction of appendiceal CT” with interest. Though the results are suggestive for the author’s conclusion, that appendiceal computed tomography (CT) can be advocated in nearly all female and many male patients, the numbers and statistics quoted in this paper warrant some critical appraisal.
According to the authors, the negative appendectomy rate was statistically lowered from 20% of patients (98/493) in the pre-CT era to 7% (15/209). But in 1997, only 123 of 209 patients had an appendiceal CT before undergoing appendectomy, and in 117, it was interpreted as positive for appendicitis. Of these, 3% (n = 3) were found to have no pathologic signs for appendicitis. On the other hand, of 86 patients undergoing appendectomy without preoperative CT scan during the same period, seven patients (8%) had a normal appendix. In our opinion, this number represents the true negative appendectomy rate that should be compared: 3% with CT versus 8% without CT during the observation period (P = .07, Pearson;P = .1, Fisher exact test), as opposed to the suggested 20% versus 7%.
Concerning the 206 patients who did have an appendiceal CT but did not undergo appendectomy, it is unclear how many of these would have undergone appendectomy without prior CT scan. What were the inclusion criteria for CT scan of the appendix?
In our opinion, the perforation rate is calculated incorrectly. The true perforation rate should be perforated appendices of all operated appendices. 2 This calculation would lead to a different distribution: 87 of 493 (18%) in 1992 through 1995 versus 28 of 209 (13%) in 1997, not a statistically significant difference.
Even regarding the appendiceal perforation rate quoted in this paper, which was 87 of 395 (22%) with appendicitis in 1992 through 1995, and declined to 28 of 194 (14%) in 1997, some questions remain about the distribution of perforated appendices to the groups “CT scan prior to surgery (114/194)” and “no CT scan prior to surgery (79/194).” If the distribution of perforated appendices was equal in the two groups, the lower perforation rate in 1997 would be independent of appendiceal CT.
One important message of this article was that adult women could benefit the most from appendiceal CT. But the numbers given are somewhat puzzling: in Table 2, four of 19 (21%) adult women underwent negative appendectomy who did not undergo appendiceal CT prior to surgery in 1997. When this number is added to the six adult females (6/67, 9%) of all others with negative appendectomy rate, the total is ten of 86 patients (12%) with negative appendectomy of patients without prior appendiceal CT. But on the same page, the negative appendectomy rate was quoted to be 8% (7/86). Which of these numbers is the correct one is unclear, but whether the drop in negative appendectomy rate is truly due to the introduction of the appendiceal CT in this subpopulation remains even more obscure.
Abdominal ultrasound, a potent diagnostic tool, was not mentioned in this article as an alternative method, but it has some potential benefits over CT. In studies including more than 1000 patients, specificity, sensivity, positive predictive value, and negative predictive value (a standard validation of a diagnostic tool, which was not given in this paper for the study group) of abdominal ultrasound was over 96%. 3,4 Similar or better results are reported regarding negative laparotomy and perforation rate, without the burden of radiographic exposure to the gonades (CT of the pelvis: skin dose of 36 mSv; organ dose for the uterus and ovaries, approximately 20 mSv 5; mutation rate 1%/Sv).
To evaluate the diagnostic power of appendiceal CT, a prospective randomized trial comparing both methods should give the best and most accurate answer.
July 9, 1999
Tim Strate MD
Claus G. Schneider
Christian Bloechle
Jakob R. Izbicki
References
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