Situs ambiguus - left isomerism

Case contributed by Hoe Han Guan


Shortness of breath, cough and fever for 3 days.

Patient Data

Age: 50 years
Gender: Male

The heart is on the left with the apex pointing towards the left side (levocardia).

The aortic arch is located at the right side

Homogeneous opacity occupies the left hypochondrium which can suggest the liver is situated at the left side.

Endotracheal tube in situ with the tip at the T3 vertebral level.

Nasogastric tube coursed at the right side of thoracic vertebra with the tips located below the right hemidiaphragm. The stomach gas bubbles located at the right hypochondrium.



  • Situs ambiguus where there are multiple splenules located in the left hypochondrium and the liver is located in the left hypochondrium.

  • Celiac trunk: only the splenic artery arises from celiac trunk, normal common hepatic artery is not seen.

  • Replaced common hepatic artery, possibly from the abdominal aorta, inferior to the origin of superior mesenteric artery,

Annotated image

Annotated images showed the relevant anatomy in situs ambiguus.

Case Discussion

Situs ambiguus (heterotaxy syndrome) can be left isomerism or right isomerism with mirroring of some left- or right-sided structures and additional abnormalities.

Careful scrutinisation of the chest radiograph (including ensuring the correct placement of the side marker) shows:

  • position of the heart and the cardiac apex

  • position of aortic knuckle

  • position of the stomach gas bubble in order to detect the situs ambiguus

This case is challenging; at an initial glance of the chest radiograph there is no dextrocardia, instead, there is normal levocardia.

Multiple anatomic variants are present in this one case, which requires the radiologist to assess all the relevant associations with heterotaxy syndrome as review areas in order to avoid satisfaction of search error.

Assessing the position of main bronchi relative to pulmonary arteries is crucial in order to decide between hyparterial or eparterial bronchi, which can reliably determine the type of heterotaxy syndrome, either right isomerism or left isomerism.

Right isomerism typically presents in early life with major cardiovascular abnormalities whereas left isomerism can present in adult life as the abnormalities are typically less significant. In this case, importantly, the muscular anterior ventricle is connected to the aorta. Left-to-right shunting due to PAPVR causes recirculation of blood through the heart but as there is no pressure overload this can be asymptomatic.

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