Situs inversus

How it works

The organs of the chest and belly are not symmetric. The heart points left, the liver sits on the right, and the stomach and spleen sit on the left. In situs inversus the whole arrangement is flipped. The heart points right, the liver is on the left, and every other organ follows¹. Because everything is reversed together, the organs still connect to each other correctly and work normally.

The left-right pattern is set in the first weeks after conception. A small pit on the embryo is lined with tiny hairs called cilia. They beat in one direction and push fluid to the left. That flow tells the embryo which side is which². If the cilia do not beat, the choice of side becomes random, and about half of those embryos end up mirrored².

About 1 in 10,000 people have situs inversus¹. Roughly a quarter of them also have primary ciliary dyskinesia, a condition in which cilia throughout the body do not move properly¹. The combination is called Kartagener syndrome, and it causes repeated sinus and chest infections². The other three-quarters have no symptoms at all. Many learn of it as adults, from a chest X-ray or a scan for something unrelated.

The main practical point is that doctors need to know. Appendicitis, for example, hurts on the left instead of the right. Some people carry a note or a medical alert bracelet for this reason¹.

History and culture

The basketball player Randy Foye has situs inversus and played in the NBA with no restrictions³. The actor Catherine O’Hara has also described having it⁴. Both were healthy and found out by chance.