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Key Points

  • Heterotaxy is an abnormality of formation of the left–right axis of the body.

  • Heterotaxy refers to any arrangement that deviates from situs solitus or complete situs inversus.

  • Left atrial isomerism or polysplenia syndrome usually has absent right-sided organs and bilaterally placed left-sided organs with multiple splenic masses along the greater curvature of the stomach.

  • Right atrial isomerism or asplenia syndrome usually has bilaterally trilobed lungs, globular central lines, severe congenital heart defects, and absent spleen.

  • Fetal echocardiography is indicated in all suspected cases of heterotaxy.

  • Delivery in a tertiary care center is recommended.


Heterotaxy is defined as any arrangement of the body organs that deviates from complete situs solitus with levocardia and dextrocardiac loop (the normal arrangement) or from complete situs inversus with dextrocardia and a levocardiac loop. During development there is a failure to form asymmetry along the left–right axis in the heterotaxy syndrome. In normal development, this asymmetry is first manifested at 2 to 23 days of gestation, with looping of the cardiac tube to the right (Gutgesell, 1990). During this same period, abdominal situs is determined (Chandra, 1974; Gray et al., 1994). The 270-degree counterclockwise rotation of the intestine about the axis of the superior mesenteric artery is completed by 10 weeks. Because looping of the cardiac tube and intestinal rotation both occur during the 4th week of gestation, defects of the cardiac situs are frequently associated with abnormal intestinal rotation. Because development of the heart is dependent on the formation of a normal left–right relationship, heterotaxy is associated with congenital heart disease in the majority of cases (Chandra, 1974; Gutgesell, 1990; Cohen et al., 2007).


There is a spectrum of defects in heterotaxy syndrome, varying from isolated levocardia with abdominal situs inversus or isolated dextrocardia with abdominal situs solitus to total absence of asymmetry along the left–right axis. The most significant forms of heterotaxy syndrome are seen in left isomerism (also known as the polysplenia syndrome) or right isomerism (also known as asplenia syndrome). The term asplenia originated from Ivemark’s (1955) initial description of cardiac malformations associated with congenital asplenia. Moller et al. (1967) subsequently reported another syndrome, also with cardiac and visceral abnormalities, but because it was associated with multiple splenic masses, it was called “polysplenia syndrome.”


Sapire et al. (1986) further described these syndromes in relation to anatomic features of the atria, such as right atrial isomerism (asplenia syndrome) and left atrial isomerism (polysplenia syndrome). This distinction was suggested because the anatomic features of the atria more reliably reflect the visceral abnormalities than does the spleen. Usually asplenia occurs in right atrial isomerism and polysplenia occurs in left atrial isomerism, but discrepancies have been reported (Caruso and Becher, 1979). In addition, each condition has been described with both the presence of a normal spleen (Laman et al., ...

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