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situs ambiguus

Thursday 23 November 2006

Definition: Situs ambiguus is the failure of asymmetry of unpaired organs and thus a condition where at least one organ shows a reversed orientation along the L–R axis. This condition has an estimated incidence at birth of 1/10,000. Situs ambiguus is frequently associated with isomerism.

Situs ambiguus is almost invariably associated with complex cardiovascular malformations as well as anomalies of the spleen and the gastrointestinal system.

Over 80% of children with situs ambiguus present with complex congenital heart disease. The spectrum of cardiac malformations that is seen in heterotaxia includes:

- transposition of the great arteries (TGA)
- double outlet right ventricle (DORV)
- double inlet left ventricle (DOLV)
- atrioventricular septal defects

  • atrial septal defect
  • ventricular septal defect

- total anomalous pulmonary venous connection

Besides the cardiac anomalies, situs ambiguus is often associated with gastrointestinal manifestations:

- right-sided stomach
- medial liver (midline liver)
- biliary tract developmental anomalies
- intestinal malrotation
- left-sided appendix
- right-sided spleen
- polysplenia
- asplenia

Case records

- Case #10300

See also

- heterotaxy (situs anomalies)
- organ morphogenesis (visceral morphogenesis)


- Peeters H, Devriendt K. Human laterality disorders. Eur J Med Genet. 2006 Sep-Oct;49(5):349-62. PMID: 16461029