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Letters to the Editor |
imonovsk
, MD, PhD
Ultrasound Unit, 3rd Polyclinic, P
íbram, Czech Republic, U Slávie 34, 26301 Dobí
, Czech Republic, e-mail: simonovsky@post.cz
Editor:
I read with great interest the article by Dr Rettenbacher and colleagues in the March 2001 issue of Radiology (1) on the limitations of outer appendiceal diameter (OAD) in diagnosing acute appendicitis. The authors concluded that an "outer appendiceal diameter [OAD] of 6 mm or more. ...provides high sensitivity but limited specificity. This diagnostic criterion is more useful in excluding acute appendicitis than in confirming it." I have a few important comments on their contribution.
First, Dr Rettenbacher and colleagues state that the OAD in control subjects ranged between 2 and 13 mm and that in 23% (55 of 240) the diameters were 6 mm or more and in 9% (21 of 240) were 7 mm or more. In their article, however, despite reporting such a frequency of grossly pathologic values for asserted normal appendices, no relevant explanation for the causes of these findings was given either in the results or in the discussion. Also, the illustrations present the reader only with some typical examples of acute appendicitis and an obviously normal appendix according to whatever criterion chosen in Figure 4 (4-mm OAD). However, no illustrations document the most important finding of their research, which is with certainty abnormally wide appendices. The reader thus can only speculate on the possible morphologic characteristics of such appendices, which is undoubtedly unfortunate with regard to the importance of an article such as this.
Provided that enough compression was applied in an attempt to express fluid and/or loosen feces, was the abnormal OAD caused, for example, by some noncompressible endoluminal material? This might be a plausible explanation because in my experience (2), I have encountered appendices containing to some degree inspissated noncompressible fecal contents at some point of their course, which resulted in the OAD exceeding any adopted upper limit of normal, while the generally accepted 3-mm mural thickness limit was maintained. A similar appearance was noted by Rioux (3).
Another possible explanation, as mentioned by Hahn et al (4), is that the reason for an abnormal OAD was a mucoid presence within the distended lumen (in patients with cystic fibrosis). Finally, some researchers (2,3,5) have noted normal appendices containing a small amount of fluid or mostly loose feces. Did Dr Rettenbacher and colleagues also encounter such appendices? Nevertheless, this alternative may not be a principal explanation because such material invariably is easily forced out of that particular part of the lumen with increased compression.
Alternatively, was an abnormal OAD value in such appendices simply the result of abnormal mural thickness? However, in my experience, I have never seen an appendix with a wall thickness exceeding 3 mm in an asymptomatic patient, and I am not aware of such an appendix to be subsequently proven as completely normal on the histopathologic report. In regard to abnormal mural thickness, I was surprised that there are no data in their report as to whether Dr Rettenbacher and colleagues encountered documented cases of spontaneously resolving appendicitis in their symptomatic patients, which I would otherwise presume to have happened in a study that comprises a substantial sample of patients (n = 98) with verified acute appendicitis.
This entity, at least in a few cases, has been frequently reported in recent years in studies (2,3,6,7) of similar or even smaller populations with true-positive findings for appendicitis. In an extension of this reasoning, can Dr Rettenbacher and colleagues rule out that it may have therefore been possible that some of their control subjects had experienced an unrecognized attack of resolved appendicitis prior to the study? Further, if such a condition (though not defined as such in the article) was encountered in the symptomatic subjects, did Dr Rettenbacher and colleagues thereafter consider those patients as healthy (ie, as symptomatic patients without acute appendicitis in their table 2)? In my opinion, such an attitude would clearly be unjustified because although on occasion acute appendicitis is witnessed to spontaneously heal, because of undisputed acute inflammatory changes within the wall at the time of the primary study, such cases cannot obviously be considered as true normal.
Further, the authors encountered five cases of catarrhal or erosive appendicitis with an OAD of less than 6 mm. However, they regarded such cases as normal because they believed that these appendices did not have the substantial histopathologic changes of the group of acutely inflamed appendices. In my opinion, however, these cases should be regarded as what they actually are, that is, cases with mild (early) acute appendicitis rather than normal cases.
Although as already mentioned, it is possible for many of the cases with early acute appendicitis to undergo spontaneous recovery (2,3,6–8), this may not be the rule for all. Moreover, support already exists for such a precaution from a robust patient outcomes study (8), which demonstrated that a great portion (38%) of the cases of acute appendicitis that resolve will develop recurrence sometime in the future. In addition, the primary goal of ultrasonography (US) is to identify the abnormal appendix as early as possible because inappropriate delay in surgery may result in perforation, with associated morbidity, mortality, and costs. Therefore, I suggest that as far as handling such appendices is concerned (ie, whether they would or would not be removed), the final discretion depends on the attending surgeon. Moreover, the method of measurement used (precision to only the nearest whole number in millimeters) probably may not be considered as ensuring enough consistency of measurement data, and thus it might have been possible for some of the appendices to suffer from significant overlap at the 6-mm OAD threshold.
In conclusion, in no way do I wish to scale down the interesting and important contribution of Dr Rettenbacher and his team of co-workers. I likewise share their view that the OAD criterion has important limitations and that to correctly diagnose acute appendicitis, several criteria should be routinely applied. However, interested readers should be provided with sufficient information on the mentioned issues to clear up potential confusion.
REFERENCES
imonovsk V. Sonographic detection of normal and abnormal appendix. Clin Radiol 1999; 54:533-539.[CrossRef][Medline]
Department of Radiology II, University Hospital Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria, e-mail: thomas.rettenbacher@uklibk.ac.at
We thank Dr imonovsk for his comments about our article (1) because he gives us the opportunity to discuss and clarify several points of interest for the readers. He mentioned in his letter that in our article, a "frequency of grossly pathologic values for asserted normal appendices" was reported. However, in our study (1), the vast majority of normal appendices with outer diameters greater than or equal to 6 mm (85%) were at 6 mm and 7 mm, which is not grossly different from the threshold value of 6 mm. With regard to Dr imonovsk’s comment about "asserted normal appendices," we would like to remark that we introduced in our study (1) a healthy control group in addition to patients with lower right quadrant pain to make it obvious that a subgroup of individuals had normal appendices.
Further, Dr imonovsk stated in his letter that the illustrations in our study (1) showed only some typical examples of acutely inflamed appendices and an obviously normal appendix. That was not the case. To keep illustrations to an essential minimum, we provided an example of a variation in diameter over the length, a thin and a thick acutely inflamed appendix, as well as a thin and a thick normal appendix (1). The example of a thick normal appendix, which was shown in Figure 5 (1), was a round appendix with an outer diameter of 8 mm in an 18-year-old healthy man. This example illustrated one possible reason for a thick appendix, namely a thick tunica mucosa indicated by the hypoechoic round center of the appendix, which was demonstrated in Figure 5 (1).
In our experience, the broad tunica mucosa in this young subject is due to lymphoid hyperplasia, which is a known reason for outer appendiceal diameters of 6 mm or more in children and young adults and which is clearly pointed out in a publication by Hahn et al (2). In this study (2), 79 of 96 children with histologically proven normal appendices with lymphatic hyperplasia had an appendiceal diameter of 6 mm or more. Figure 5 of our study (1) further gives Dr imonovsk an example of a normal appendix with a wall thickness of more than 3 mm, namely 4 mm.
However, in our study (1), lymphatic hyperplasia was not the main reason for outer diameters of 6 mm or more in normal appendices because the majority of patients and control subjects were adults. The most common reason was contained gas and/or feces and/or fluid, resulting in noncollapsed appendices measuring 6 mm or more in a considerable percentage of the subjects. We do not agree with Dr imonovsk that gas, feces, and fluid within the appendiceal lumen can be easily expressed with the US transducer in most cases.
In our experience, compressibility in a part or along the whole length of normal appendices is often not demonstrable. With regard to this topic, we would like to offer the following explanations. If a part or the whole length of an appendix is located between the US transducer and the psoas muscle, the appendiceal lumen is either collapsed or is usually easily compressible. However, the distal part or the whole length of the appendix is frequently located medially to the iliac vessels. In this location, the usually round and often gas- and/or feces- and/or fluid-filled normal appendix cannot be compressed sufficiently against a fixed anatomic structure such as the psoas muscle to express appendiceal contents. In addition, normal appendices can be so movable that they tend to disappear out of the field of view if compression is applied during US scanning. Furthermore, compressibility of the appendix often cannot be demonstrated sufficiently in obese patients. Another important reason for a fairly wide range in diameter is simply that appendiceal size varies from individual to individual.
Dr imonovsk questioned if we had encountered cases of spontaneously resolving appendicitis. In our study (1), we did not. Probably due to the close cooperation and confidence between the US staff and our surgeons, all patients with US findings suggestive of acute appendicitis underwent appendectomy. With regard to spontaneously resolving acute appendicitis, it would also seem important to address the question of whether we encountered patients in whom concomitant appendiceal wall thickening was documented. In fact, we did.
In our study (1), we had several patients with differential diagnoses such as ileocolitis or mesenteric adenitis in which moderate concomitant appendiceal wall thickening and its subsequent disappearance were documented. However, we share the opinion of Dr imonovsk that imaging-documented cases of resolving acute appendicitis should be excluded from the group of noninflamed appendices.
Dr imonovsk further questioned whether we could eliminate the possibility that some of our control subjects had experienced an unrecognized attack of resolving acute appendicitis prior to the study. We cannot. However, in our experience and according to the literature, patients with spontaneously resolving acute appendicitis usually present with a normal imaging appearance of the appendix after inflammation has resolved (3,4). Therefore, Dr imonovsk’s argument cannot be a valid reason for outer appendiceal diameters of 6 mm or more in our control subjects.
Dr imonovsk suggested adding the five cases with catarrhal or erosive appendicitis to the study group of acutely inflamed appendices because they represent cases with early acute appendicitis. After considerable thought, we decided not to in our study (1). For example, three of these five patients with questionable appendicitis had a duration of symptoms of 7, 5, and 4 days before they underwent appendectomy. Surgery did not reveal any abnormality, and on the basis of findings from histologic examination catarrhal appendicitis was diagnosed. In our opinion, the long period of symptoms argues against the presumption that these cases represent cases of early appendicitis that bear a risk of developing severe inflammation and perforation.
With regard to the criticism of rounding off the numbers of appendiceal diameters to the nearest whole number in millimeters, we would like to remark that the setting of electronic calipers in our study (1) offered measurements to a tenth of a millimeter. However, in our experience, assessment of outer borders of appendices, especially in those that are acutely inflamed, cannot be performed accurately enough to yield a tenth of a millimeter as reliable data. We therefore rounded off the numbers, which is in accordance with the practice of most publications.
Finally, we appreciate the opinion of Dr imonovsk that US imaging of the appendix should consider several US criteria simultaneously. To give optimal support to clinicians, sophisticated applications of several US criteria have to be performed to correctly interpret the various appearances of acutely inflamed and normal appendices as well as to consider the numerous differential diagnoses.
REFERENCES
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