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Situs anomalies present a diagnostic challenge to radiologists because of the overlapping spectrum of findings commonly seen in asplenia and polysplenia. In a series of 21 patients with a diagnosis of heterotaxy syndrome, all 11 asplenic patients and seven of 10 polysplenic patients had congenital heart disease. Although there was a variety of complex congenital heart disease, the most common type in both patient groups was a common atrioventricular canal. In both groups, the laterality of the aorta and stomach was quite variable, but intestinal malrotation was a constant feature. In 11 asplenic patients, the most frequent findings were a bridging liver (10 cases), absent spleen (10 cases), and left-sided inferior vena cava (nine cases). Only seven of these patients had an aorta ipsilateral to the inferior vena cava, contrary to previous thought that this finding was specific for asplenia. In the 10 polysplenic patients, bridging livers were less frequent (five cases), single (six cases) or multiple (four cases) spleens were seen, and azygous continuation with interruption of the inferior vena cava was usually present (eight cases). Although not pathognomonic of polysplenia, inferior 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 syndromes encompass an overlapping spectrum that needs to be described individually and may best be called heterotaxy syndrome.

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Intestinal malrotation, which is defined by a congenital abnormal position of the duodenojejunal junction, may lead to midgut volvulus, a potentially life-threatening complication. An evaluation for malrotation is part of every upper gastrointestinal (GI) tract examination in pediatric patients, particularly neonates and infants. Although the diagnosis of malrotation is often straightforward, the imaging features in approximately 15% of upper GI tract examinations are equivocal and lead to a false-positive or false-negative interpretation. The clinical manifestations and upper GI tract findings of malrotation in older children and adults are less specific than are those in younger patients, and for this reason diagnosis of the condition may be more difficult. Successful differentiation between a normal variant and malrotation requires the use of optimal techniques in acquiring and interpreting the upper GI series. Familiarity with the upper GI series appearance of both normal and abnormal anatomic variants allows the radiologist to increase both diagnostic accuracy and confidence in the diagnosis of malrotation.