Importance of Appropriate, Detailed Description in the Setting of Isomerism.

Abstract

Editor: I read with great interest the article entitled “Tracheobronchial Branching Abnormalities: Lobebased Classification Scheme” by Chassagnon and colleagues (1) in the March-April issue of RadioGraphics. This article is very well written, and the authors must be commended for a quality article. It is in the discussion of isomerism, also known as heterotaxy, however, where there are some inaccuracies. What was once called heterotaxy is best described as isomerism, which is further segregated into the subsets of right or left isomerism (2,3). Isomerism is subcategorized on the basis of the morphology of the atrial appendages and whether there are two morphologically left or right appendages. The importance of such segregation is that it allows for “syndromic clustering” of other anatomic and functional abnormalities (4). Although this syndromic clustering includes splenic anatomy, it should be noted that right isomerism is not synonymous with absence of a spleen and that left isomerism is not synonymous with the presence of multiple spleens, as implied by Chassagnon and colleagues (1). Indeed, either right or left isomerism can be associated with absence of a spleen, multiple spleens, or even a solitary spleen. Interestingly, splenic function may be abnormal with any of these arrangements (5). Chassagnon and colleagues (1) also use the term situs ambiguus, which should be avoided because there is no ambiguity in the location of the organs; the location is known. This term does not hold any value because it does not actually convey any information. It is important for the radiologist to actually describe the precise location of the specific organs, which can readily be done. In the absence of optimal imaging of the atrial appendages, other anatomic features can be used to help segregate isomerism into left or right, particularly the bronchopulmonary anatomic structures (6). The presence of a coronary sinus has been noted to always be associated with left isomerism, and the presence of a eustachian valve or terminal crest has been noted to always be associated with right isomerism. Noncardiac findings can also assist in determining the sidedness of isomerism (7,8). Because these classifications allow prediction of, early detection of, and early intervention for future arrhythmias, neurodevelopmental outcomes, and other visceral function, it is of utmost importance that radiologists describe the findings appropriately in a detailed fashion and are able to provide accurate classification of isomerism by using the proper terminology (9–11).