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Situs inversus (also called situs transversus) is a rare congenital condition in which the major visceral organs are reversed or mirrored from their normal positions. The normal arrangement is known as situs solitus. In other rare cases, in a condition known as situs ambiguus or heterotaxy, situs cannot be determined. Situs inversus should not be confused with a mislabelled chest X-ray. The term situs inversus is a short form of the Latin phrase, "situs inversus viscerum" meaning "inverted position of the internal organs". Dextrocardia (the heart being located on the right side of the thorax) was first recognised by Marco Severino in 1643. However, situs invertus was first described more than a century later by Matthew Baillie. The prevalence of situs inversus varies among different populations but is less than 1 in 10,000 people.
Effect on anatomy The condition affects all major structures within the thorax and abdomen. Generally, the organs are simply transposed through the sagittal plane. The heart is located on the right side of the thorax, the stomach and spleen on the right side of the abdomen and the liver and gall bladder on the left side. The left lung is trilobed and the right lung bilobed, and blood vessels, nerves, lymphatics and the intestines are also inverted. If the heart is swapped to the right side of the thorax, it is known as situs inversus with dextrocardia or situs inversus totalis. If the heart remains in the normal left side of the thorax, a much rarer condition (1 in 22,000 cases of situs inversus), it is known as situs inversus with levocardia. Situs inversus with levocardia, or dextrocardia without situs inversus, present much higher rates of congenital defects than situs inversus with dextrocardia. Significance
Kartagener syndrome About 25% of individuals with situs inversus have an underlying condition known as primary ciliary dyskinesia (PCD). PCD is a dysfunction of the cilia that manifests itself during the embryologic phase of development. Normally-functioning cilia determine the position of the internal organs during early embryological development, and so individuals with PCD have a 50% chance of developing situs inversus. If they do, they are said to have Kartagener syndrome, characterized by the triad of situs inversus, chronic sinusitis, and bronchiectasis. Cilia are also responsible for clearing mucus from the lung, and the dysfunction causes increased susceptibility to lung infections. Male sufferers of PCD are often infertile: the cilia that make up the tail of individual sperm cells are also defective, thus rendering the sperm ineffective. See also Notable persons with situs inversus Notable individuals with documented cases of situs inversus include: | |||||||||||||||||||||||||||||||
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