Xenbase Image ID: 153580

Figure 1. Asymmetric Disposition of Visceral Organs in Humans The normal disposition of organs is called situs solitus (A). The right lung has three lobes, whereas the left lung (indicated in a different color for clarity) has two. In addition, the apex of the heart points to the left side, the liver is on the right side, and the stomach and spleen are on the left side. Although not shown in the figure, the gut coils counterclockwise in the abdominal cavity. In right isomerism (B), also called asplenia syndrome, the heart and lungs are double-right (as indicated by the structure of the heart chambers and by both lungs having three lobes), as is the liver, which is generally found in a midline position. The stomach may be located on either side or in the midline, and the spleen is absent. In left isomerism (C), also called polysplenia syndrome, the heart and lungs are double-left, the liver may be double-left, located in a midline position, or normal, and the stomach is usually found in a midline position. There is always more than one spleen (termed splenules), although multilobulated single spleens may also occur. Situs inversus refers to the complete mirror-image reversal of organ asymmetry (D). Since laterality defects are highly variable, the figure depicts simplified cases, and is not intended to portray accurately the whole range of possible defects. The terms situs inversus and right or left isomerism can also be used to describe laterality defects in individual organs, even if they are not included in specific syndromes. Adapted from Brown and Anderson, 1999. Image published in: Capdevila J et al. (2000) Copyright © 2000. Image reproduced with permission of the Publisher, Elsevier B. V. Larger Image Printer Friendly View

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