Heterotaxy syndrome -- asplenia and polysplenia as indicators of visceral malposition and complex congenital heart disease.

Heterotaxy results from failure of the developing embryo to establish normal left-right asymmetry. Typical manifestations include abnormal symmetry and malposition of the thoraco-abdominal organs and vessels, complex congenital heart disease and extracardiac defects involving midline-associated structures. The spleen is almost always affected, and there is syndromic clustering of the malformations corresponding to the type of splenic abnormality present. This review outlines the embryologic and genetic background of the heterotaxy syndrome as well as the characteristic anatomic features, clinical manifestations, and diagnostic clues of its two main presentations with asplenia or polysplenia.