Situs revisited: Imaging of the heterotaxy syndrome

Situs anomalies present a diagnostic challenge to radiologists because of t he overlapping spectrum of findings commonly seen in asplenia and polysplen ia. In a series of 21 patients with a diagnosis of heterotaxy syndrome, all II asplenic patients and seven of 10 polysplenic patients had congenital h eart disease. Although there was a variety of complex congenital heart dise ase, the most common type in both patient groups was a common atrioventricu lar canal. In both groups, the laterality of the aorta and stomach was quit e variable, but intestinal malrotation was a constant feature. In 11 asplen ic patients, the most frequent findings were a bridging liver (10 cases), a bsent spleen (10 cases), and left-sided inferior vena cava (nine cases). On ly seven of these patients had an aorta ipsilateral to the inferior vena ca va, contrary to previous thought that this finding was specific for aspleni a, In the 10 polysplenic patients, bridging. livers were less frequent (fiv e cases), single (six cases) or multiple (four cases) spleens were seen, an d azygous continuation with interruption of the inferior vena cava was usua lly present (eight cases). Although not pathognomonic of polysplenia, infer ior vena cava interruption with azygous or hemiazygous continuation is the most common anatomic finding of this condition. Although the terms asplenia and polysplenia are helpful in suggesting the typical anatomy, both syndro mes encompass an overlapping spectrum that needs to be described individual ly and may best be called heterotaxy syndrome.