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Situs inversus (also called situs transversus or oppositus) is a congenital condition in which the major visceral organs are reversed or mirror image from their normal positions. The normal arrangement of internal organs is known as situs solitus. Many people with situs inversus have no medical symptoms resulting from the condition, although cardiac problems are the most common complication. Until the advent of modern medicine, it was usually undiagnosed.
Situs inversus is found in about 0.01% of the population, or about 1 person in 10,000. In the most common situation, situs inversus totalis, it involves complete transposition (right to left reversal) of all of the viscera. The heart is not in its usual position in the left chest, but is on the right, a condition known as dextrocardia (). Because the relationship between the organs is not changed, most people with situs inversus have no associated medical symptoms or complications.
An uncommon form of situs inversus is isolated levocardia, in which the position of the heart is not mirrored alongside the other organs. Isolated levocardia carries a risk of heart defects, and so patients with the condition may require surgery to correct them.
In rarer cases such as situs ambiguus or heterotaxy, situs cannot be determined. In these patients, the liver may be midline, the spleen absent or multiple, and the bowel malrotated. Often, structures are duplicated or absent altogether. This is more likely to cause medical problems than situs inversus totalis.
Many people with situs inversus totalis are unaware of their unusual anatomy until they seek medical attention for an unrelated condition, such as a rib fracture or a bout of appendicitis. The condition may also be discovered during the administration of certain medicines or during tests such as a barium meal or enema. medscapestatic.com; Situs inversus of the large intestine discovered after administering a barium enema , eMedicine The reversal of the organs may then lead to some confusion, as many signs and symptoms will be on the atypical side. For example, if an individual with situs inversus develops appendicitis, they will present to the physician with lower left abdominal pain, since that is where their appendix lies.Intestinal malrotation can also cause the appendix to be on the left side. Thus, in the event of a medical problem, the knowledge that the individual has situs inversus'' can expedite diagnosis. People with this rare condition should inform their physician before an examination, so the doctor can redirect their search for and other signs. Wearing a medical identification tag can help inform health care providers in the event the person is unable to communicate.
Situs inversus also complicates organ transplantation operations as donor organs will more likely come from situs solitus (normal) donors. As hearts and livers are Chirality, geometric problems arise placing an organ into a cavity shaped in the mirror image. For example, a person who requires a heart transplant needs all their great vessels reattached to the donor heart. However, the orientation of these vessels in a person with situs inversus is reversed, necessitating steps so that the blood vessels join properly.
About 25% of individuals with situs inversus have an underlying condition known as primary ciliary dyskinesia (PCD). PCD is a dysfunction of the cilium that occurs during early embryonic development. Normally functioning cilia determine the position of the internal organs during early development, and so embryos with PCD have a 50% chance of developing situs inversus. If they do, they are said to have Kartagener syndrome, characterized by the Medical 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. Kartagener syndrome can also manifest with male infertility as functional cilia are required for proper sperm flagella function.
A marked increase in cases was observed several months after the lifting of the zero-COVID-19 policy in China, which coincided with a rise in SARS-CoV-2 infections. This rare clinical evidence suggests a possible link between infection during pregnancy and the development of situs inversus in the fetus, specifically during gestational weeks 4–6, the critical period for organ positioning.
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 on the normal left side of the thorax, a much rarer condition (1 in 2,000,000 of the general population), it is known as " situs inversus with levocardia" or " situs inversus incompletus".
Situs inversus of the optic disc may occur unilaterally or bilaterally, associated with reduced binocularity and stereoacuity resembling monofixation syndrome. It is characterized by emergence of the retinal vessels in an anomalous direction (from the nasal rather than the temporal aspect) with dysversion (tilt) of the optic disc.
Situs inversus does not appear to significantly affect rates of handedness. Based on a 2004 study documenting situs inversus in individuals with primary ciliary dyskinesia, the proportion of right-handedness among those with situs inversus did not differ significantly from that of those with situs solitus. A more recent 2023 study failed to find statistically significant differences in cognition, albeit left-handedness was significantly more common at 26% compared to the 10.6% of general population.
Any potential treatment would involve a complete and highly invasive surgical rearrangement of the internal viscera of the patient. Such a procedure is unnecessary, given that situs inversus rarely causes any additional symptoms. No treatment, medical or surgical, is prescribed for situs inversus individuals, with medical professionals instead treating any other symptoms the patient may have with awareness of the unique anatomy of the patient.
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