Situs inversus, (rare plural: sitūs inversi) short form of the Latin “situs inversus viscerum”, is a term used to describe the inverted position of chest and abdominal organs.
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Terminology
The condition is called situs inversus totalis when there is a total transposition of abdominal and thoracic viscera (mirror image of internal organs' normal positioning). Normal positioning of the organs - as found in the majority of individuals is called situs solitus.
Much more rarely is transposition of the abdominal organs with a 'normal' left-sided heart, known variously as situs inversus incompletus, situs inversus partialis, or simply situs inversus with laevocardia 7.
Epidemiology
Situs inversus has a prevalence of approximately 1:10,000 and is higher in males (~1.5:1) 8.
Associations
Situs inversus is usually associated with dextrocardia (true mirror image) with only 3-5% incidence of congenital heart disease, most commonly transposition of the great vessels. Of these patients, 80% have a right-sided aortic arch. Situs inversus with laevocardia (which is much rarer: 0.00005%) congenital heart disease is found in 95% of patients 4.
Up to 20% of patients with situs inversus can have Kartagener syndrome 3 which comprises a subgroup of primary ciliary dyskinesia.
Situs inversus can be associated with both asplenia 5 or polysplenia (rarely) 6.
Complete situs inversus is associated with the absence of inferior vena cava 5.
Clinical presentation
Situs inversus is typically asymptomatic 8 unless associated with congenital heart disease.
Radiographic features
Plain radiograph
Imaging features on the chest radiograph to be evaluated are:
location of the heart apex
location of the aortic arch
locations of stomach bubble and liver
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