Clinical Presentation and Therapy of Anomalies of the Situs

Situs abnormalities may occur in many and most often more complex congenital cardiac malformations. These conditions are collectively referred to as heterotaxy syndromes, derived from the Greek words "heteros" meaning different and "taxos" meaning orientation or arrangement. Clinically, heterotaxy spectrum encompasses defects in the left-right laterality and arrangement of visceral organs. "Situs" is derived from Latin and is the place where something exists or originates. In human anatomy, situs can be solitus (derived from Latin, meaning "normal"), inversus, or ambiguus. Heterotaxy syndrome represents an intermediate arrangement of internal organs between situs solitus and situs inversus, also known as "situs ambiguous." Situs ambiguus describes an abnormal distribution of major visceral organs within the chest and abdomen. The determination of situs as normal, inversus, or ambiguus is primarily based on the location of unpaired organs such as the spleen, liver, stomach, and intestines. Diagnosis is made by clinical examination, echocardiography, a chest X-ray (position of the heart, stomach, and liver), and ultrasound of the abdominal organs. Situs is considered solitus if the left atrium, spleen, stomach, and the trilobed lung are on the left side and the liver and bilobed lung are on the right side. Situs ambiguus is present if the location of unpaired structures is random or indeterminate even after detailed and appropriate imaging. Situs inversus results when the arrangement of the thoracic and abdominal organs is mirrored. Individuals with situs inversus or situs solitus do not experience fatal dysfunction of their organ systems, as general anatomy and morphology of the abdominothoracic organ-vessel systems are conserved.