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 levocardia 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 levocardia (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 chest radiograph to be evaluated are:
location of the heart apex
location of the aortic arch
locations of stomach bubble and liver