ABSTRACT
Situs inversus, malrotations, and malpositions of the heart Compared to the most common condition of situs solitus and levocardia, there is very rarely a situation where all organs are rotated exactly to the opposite side, leading to a mirror-image arrangement. This situation is called situs inversus. When this mirror-image rotation of abdominal and intrathoracic organs is complete, the liver and inferior vena cava are on the left, whereas the stomach and the descending aorta are on the right ( Figures 16.2 and 16.3 ). Since the inferior vena cava and the right atrium are concordant, the right atrium and right ventricle are on the left anteriorly and the left atrium and left ventricle are on the right posteriorly and the heart axis points to the right anterior thorax, a situation called dextrocardia ( Figure 16.3 ) (mirror-image dextrocardia or situs inversus with dextrocardia, or situs inversus completus). In these conditions associated heart defects are rare. The true incidence of this situation is low, but also not exactly known, since persons with this abnormality are asymptomatic and are not identified until an X-ray, ultrasound, or medical intervention is performed. Because this condition is extremely rare, it can be recommended that, before making this diagnosis, the examiner checks the fetal position and the transducer orientation. According to our experience, we have found
Figure 16.1 The two important planes in assessing isomerism and other cardiac malpositions. The normal sonoanatomy of the upper abdomen with situs solitus (left) and the heart in levocardia (right). R, right; L, left; ST, stomach; VCI, inferior vena cava; AO, aorta; RV, right ventricle; LV, left ventricle.
