Heterotaxy

Situs ambiguus
Classification and external resources
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Situs ambiguus or situs ambiguous, also known as heterotaxy or heterotaxia, is a rare congenital defect in which the major visceral organs are distributed abnormally within the chest and abdomen. Heterotaxy in general refers to any defect of left-right laterality and arrangement of the visceral organs. This does not include the congenital defect situs inversus, which results when arrangement of the organs in the abdomen and chest are mirrored, so the positions are opposite the normal placement. Situs inversus is the mirror image of situs solitus, which is normal asymmetric distribution of the abdominothoracic visceral organs. Patients with situs ambiguous are considered isomeric in that they have organs with 2-right-sides or 2-left-sides, most commonly observed in relation to the atria of the heart.

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. Unfortunately, due to abnormal arrangement of organs in situs ambiguous, orientation across the left-right axis of the body is disrupted early in fetal development, resulting in severely flawed cardiac development and function in 50-80% of cases. They also experience complications with systemic and pulmonary blood vessels, significant morbidity, and sometimes death. All patients with situs ambiguous lack lateralization and symmetry of organs in the abdominal and thoracic cavities and are clinically considered to have a form of heterotaxy syndrome.

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