Heterotaxy syndrome

Heterotaxy syndromes refer to abnormal left/right distribution of thoracic and abdominal organs that is neither situs solitus nor situs inversus. They are frequently associated with congenital heart disease and other visceral abnormalities.

Terminology

Isomerism implies mirrored organs, and can be defined as mirrored atrial appendages, e.g. bilateral morphological right atrial appendages in right isomerism. In practice, atrial appendage morphology cannot always be determined. Many patients with abnormal situs do not have mirror-image morphology and this is referred to as situs ambiguus. Congenital heart disease and splenic anomalies are frequently associated giving rise to the term cardiosplenic syndrome. There are many individual variations, and each case should be individually documented.

Epidemiology

The true incidence is not known, but some sources have estimated it to be around 1 per 8,000-25,000 live births. These variations result from disruption of the left/right axis during early embryological developmental with most cases being sporadic. Approximately 20-25% are associated with the immotile cilia syndrome (including Kartagener syndrome).

Clinical presentation

This is dependent on severity of the isomerism and presence of associated abnormalities. Cyanotic congenital heart disease is the main presentation in right isomerism. Left isomerism tends to present later in childhood or even in adulthood since it is associated with less severe congenital heart disease. Intestinal malrotation with midgut volvulus may be a presenting feature.

Pathology

Bronchial anatomy as a key

Bronchial anatomy is easily determined and generally reflects atrial situs. The bronchial anatomy on the left and right can be recognised on a well-penetrated radiograph and consists of two main bronchi that are anatomically different:

• hyparterial bronchus (below artery): supplies the bilobed left lung

• eparterial bronchus (above the artery): supplies the trilobed right lung

In isomerism there is mirroring of either the left lung with its hyparterial bronchus or the right lung with its eparterial bronchus. The left or right atria are also commonly duplicated and there are common associated abdominal anomalies below the diaphragm ¹.

Radiographic features

There is duplication of the left or right-sided intrathoracic contents and associated abdominal anomalies. Classically, there is malposition and morphological abnormality of the liver and spleen. Vascular anomalies such as duplicated SVC are common¹.

Left isomerism

Known as polysplenia syndrome:

• multiple splenules without a parent spleen

• azygos or hemiazygos continuation of the inferior vena cava

• bilateral hyparterial bronchi

• bilateral bilobed lungs

• bilateral pulmonary/left atria

• midline/transverse liver

• intestinal malrotation

Right isomerism

Known as asplenia syndrome:

• severe cyanotic congenital heart diseases

• absence of spleen

• bilateral eparterial bronchi

• bilateral trilobed lungs

• bilateral right atria

• midline/transverse liver

• intestinal malrotation

Imaging workup

Assessment of the intrathoracic contents can be made with plain film, echocardiography, CT, and MRI as well as angiography. Below the diaphragm, the abdominal contents can be imaged with ultrasound, GI contrast studies, CT and MRI.

A minimal workup should include ¹:

• chest radiograph

• echocardiogram: to assess for congenital heart disease

• abdominal ultrasound: to assess intra-abdominal contents (especially spleen)

• upper GI series: to rule out malrotation

Treatment and prognosis

Treatment is dependent on the malformations and the impact that they have clinically. Specific treatment of congenital heart disease can be seen in their separate articles.

Right isomerism carries porrerpoorer prognosis than left isomerism as it has higher association with congenital heart diseases.

See also

• situs classification

  • situs solitus

  • situs inversus

• isomerism

• congenital heart disease