One person in 10,000 carries every major organ in mirror image
In situs inversus the heart sits on the right, the liver on the left and even the lungs swap their lobe counts. Because everything flips together, most people with it feel perfectly well and only learn the truth when appendicitis hurts on the wrong side of the belly.
The standard layout of the body's organs is called situs solitus. In situs inversus totalis, found in roughly 0.01 percent of people, the whole arrangement is reflected across the body's midline: stomach and spleen move to the right, liver and gallbladder to the left, the left lung gains the third lobe normally found on the right, and blood vessels, nerves and lymph channels follow suit. Since the organs keep their relationships to one another, the body generally works normally. The Latin name is a shortening of a phrase meaning inverted position of the internal organs.
The trouble comes with partial versions. If the heart stays on the left while everything else flips, a variant affecting about one person in two million, congenital heart disease occurs in 95 percent of cases. In heterotaxy, where the arrangement cannot be pinned down at all, the liver may sit in the middle and the spleen may be missing or multiplied. Even full reversal carries a 5 to 10 percent rate of heart defects. One Oregon woman with the heart-on-the-left form lived to 99 without knowing; students discovered it while dissecting her donated body.
Cilia, tiny beating hairs, set organ positions early in embryonic life. About a quarter of people with situs inversus have primary ciliary dyskinesia, in which cilia malfunction; half of embryos with that disorder end up reversed, and the combination with chronic sinusitis and bronchiectasis is known as Kartagener syndrome. The condition usually passes down in an autosomal recessive pattern, though it can also be X-linked or appear in mirror-image identical twins.
Doctors can confirm it by X-ray, ultrasound, CT or MRI, and no treatment is given for the reversal itself. It does complicate transplants, since a donor heart or liver has the opposite handedness to the cavity it must fit. Leonardo da Vinci drew a right-sided heart, and Matthew Baillie described the full condition more than a century after Marco Aurelio Severino recognised dextrocardia in 1643. Studies on handedness conflict: one from 2023 found 26 percent of people with the condition were left-handed.
Source: Situs inversus
