Situs inversus, a rare anomaly (0.01% prevalence) is simply speaking, the situation in which the asymmetric organs of the chest and abdomen are a mirror image of their normal arrangement. It is generally an autosomal recessive genetic condition, although it can be X-linked or found in identical “mirror” twins.

Usually SI is 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. SI with levocardia (which is much rarer – 0.00005%) congenital heart disease is found in 95% of patients. (see situs classification)

Twenty percent of patients with SI have Kartagener’s syndrome – subgroup of primary ciliary dyskinesia
Features on CXR to be evaluated are:
1. location of apex of heart
2. location of aortic arch
3. location of stomach bubble / liver

2. Yokoyama T, Copeland NG, Jenkins NA, Montgomery CA, Elder FF, Overbeek PA (1993). “Reversal of left-right asymmetry: a situs inversus mutation”. Science 260 (5108): 679-82
Credit: Dr Frank Gaillard