Situs Inversus Totalis

Abstract

EXTERNALLY, THE HUMAN BODY appears symmetric; if a line is drawn down the middle of the body, each side appears identical. However, this is not true of the internal anatomy. For example, there is one heart, which lies in the left chest, one liver, in the right abdomen, and one stomach, in the left abdomen. The term situs refers to the position or location of an organ, specifically, the position of the atria and abdominal viscera in relation to the midline of the body.1 There are three types of situs: solitus, inversus, and ambiguous. Situs solitus refers to the normal arrangement of organs, with the right atrium, liver, gallbladder, trilobed lung, and inferior vena cava on the right side and the left atrium, stomach, spleen, bilobed lung, and descending aorta on the left side (Figures 1–3). Situs inversus totalis refers to a mirror image reversal of the normal position of the internal organs (Figures 4 and 5). 1 The incidence of situs inversus totalis is 1 in every 8,000 to 25,000 births, and the condition is most often diagnosed by radiographic examination.2Situs ambiguous, often referred to as heterotaxia, is the random arrangement of the internal organs and is associated with splenic abnormalities and congenital heart disease.3 The purpose of this column is to discuss the embryology, pathophysiology, and diagnosis of situs inversus totalis and to review a case study with radiographic findings.