Situs inversus | |
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Situs inversus causes the positions of the heart and lungs to be mirrored. | |
Specialty | Medical genetics |
Causes | Genes |
Frequency | 0.01% |
Situs inversus (also called situs transversus or oppositus) is a congenital condition in which the major visceral organs are reversed or mirrored from their normal positions. The normal arrangement of internal organs is known as situs solitus . Although cardiac problems are more common, many people with situs inversus have no medical symptoms or complications resulting from the condition, and 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 (literally, "right-hearted"). Because the relationship between the organs is not changed, most people with situs inversus have no associated medical symptoms or complications. [1]
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. [2]
In the absence of congenital heart defects, individuals with situs inversus are homeostatically normal, and can live standard healthy lives, without any complications related to their medical condition. There is a 5–10% prevalence of congenital heart disease in individuals with situs inversus totalis, most commonly transposition of the great vessels. The incidence of congenital heart disease is 95% in situs inversus with levocardia.[ citation needed ]
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. [3] 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. [note 1] 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 doctors before an examination, so the doctor can redirect their search for heart sounds and other signs. Wearing a medical identification tag can help inform health care providers in the event the person is unable to communicate.[ citation needed ]
Situs inversus also complicates organ transplantation operations as donor organs will more likely come from situs solitus (normal) donors. As hearts and livers are chiral, 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.
Situs inversus is generally an autosomal recessive genetic condition, although it can be X-linked or found in identical "mirror image" twins. [4]
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 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 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.[ citation needed ]
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 heart's normal right atrium occurs on the left, and the left atrium is on the right. The lung anatomy is reversed and the left lung has three lobes while the right lung has two lobes. The intestines and other internal structures are also reversed from the normal, and the blood vessels, nerves, and lymphatics are also transposed.
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. [5]
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. [6]
Diagnosis of situs inversus can be made using imaging techniques such as x-ray, ultrasound, CT scan, and magnetic resonance imaging (MRI). [7]
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.[ citation needed ]
Situs inversus is rare, affecting 0.01% of the population. [8] [9]
Dextrocardia (the heart being located on the right side of the thorax) was seen and drawn by Leonardo da Vinci,[ citation needed ] and then recognised by Marco Aurelio Severino in 1643. Situs inversus was first described more than a century later by Matthew Baillie. [2]
The term situs inversus is a short form of the Latin phrase situs inversus viscerum, meaning "inverted position of the internal organs".
Notable individuals with documented cases of situs inversus include:
The cilium, is a membrane-bound organelle found on most types of eukaryotic cell. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projection that extends from the surface of the much larger cell body. Eukaryotic flagella found on sperm cells and many protozoans have a similar structure to motile cilia that enables swimming through liquids; they are longer than cilia and have a different undulating motion.
Dextrocardia is a rare congenital condition in which the apex of the heart is located on the right side of the body, rather than the more typical placement towards the left. There are two main types of dextrocardia: dextrocardia of embryonic arrest and dextrocardia situs inversus. Dextrocardia situs inversus is further divided.
Primary ciliary dyskinesia (PCD) is a rare, autosomal recessive genetic ciliopathy, that causes defects in the action of cilia lining the upper and lower respiratory tract, sinuses, Eustachian tube, middle ear, Fallopian tube, and flagella of sperm cells. The alternative name of "immotile ciliary syndrome" is no longer favored as the cilia do have movement, but are merely inefficient or unsynchronized. When accompanied by situs inversus the condition is known as Kartagener syndrome.
Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO). It is common in patients with a congenital atrial septal aneurysm (ASA).
The ductus arteriosus, also called the ductus Botalli, named after the Italian physiologist Leonardo Botallo, is a blood vessel in the developing fetus connecting the trunk of the pulmonary artery to the proximal descending aorta. It allows most of the blood from the right ventricle to bypass the fetus's fluid-filled non-functioning lungs. Upon closure at birth, it becomes the ligamentum arteriosum.
A congenital heart defect (CHD), also known as a congenital heart anomaly, congenital cardiovascular malformation, and congenital heart disease, is a defect in the structure of the heart or great vessels that is present at birth. A congenital heart defect is classed as a cardiovascular disease. Signs and symptoms depend on the specific type of defect. Symptoms can vary from none to life-threatening. When present, symptoms are variable and may include rapid breathing, bluish skin (cyanosis), poor weight gain, and feeling tired. CHD does not cause chest pain. Most congenital heart defects are not associated with other diseases. A complication of CHD is heart failure.
Situs ambiguus is a rare congenital defect in which the major visceral organs are distributed abnormally within the chest and abdomen. Clinically heterotaxy spectrum generally refers to any defect of Left-right asymmetry and arrangement of the visceral organs; however, classical heterotaxy requires multiple organs to be affected. This does not include the congenital defect situs inversus, which results when arrangement of all the organs in the abdomen and chest are mirrored, so the positions are opposite the normal placement. Situs inversus is the mirror image of situs solitus, which is normal asymmetric distribution of the abdominothoracic visceral organs. Situs ambiguus can also be subdivided into left-isomerism and right isomerism based on the defects observed in the spleen, lungs and atria of the heart.
Transposition of the great vessels (TGV) is a group of congenital heart defects involving an abnormal spatial arrangement of any of the great vessels: superior and/or inferior venae cavae, pulmonary artery, pulmonary veins, and aorta. Congenital heart diseases involving only the primary arteries belong to a sub-group called transposition of the great arteries (TGA), which is considered the most common congenital heart lesion that presents in neonates.
Situs solitus is the medical term referring to the normal position of thoracic and abdominal organs. Anatomically, this means that the heart is on the left with the pulmonary atrium on the right and the systemic atrium on the left along with the cardiac apex. Right-sided organs are the liver, the gall bladder and a trilobed lung as well as the inferior vena cava, while left-sided organs are the stomach, single spleen, a bilobed lung, and the aorta.
A right-to-left shunt is a cardiac shunt which allows blood to flow from the right heart to the left heart. This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptiles.
Lefty are a class of proteins that are closely related members of the TGF-beta superfamily of growth factors. These proteins are secreted and play a role in left-right asymmetry determination of organ systems during development. Mutations of the genes encoding these proteins have been associated with left-right axis malformations, particularly in the heart and lungs.
Levocardia refers to the most common location of the human heart, on the left side of the thoracic cavity. This is opposed to dextrocardia, in which the heart is in the right side. Neither levocardia nor dextrocardia are indicative of the orientation of the visceral organs, which can be in situs solitus, where the remainder of the organs are on normal side as well; or situs inversus, in which the viscera are on the opposite side as normal. The latter condition may or may not be associated with clinically relevant abnormalities.
Renal–hepatic–pancreatic dysplasia is an autosomal recessive congenital disorder characterized by pancreatic fibrosis, renal dysplasia and hepatic dysgenesis. An association with NPHP3 has been described. It was characterized in 1959.
Pulmonary artery stenosis (PAS) is a narrowing of the pulmonary artery. The pulmonary artery is a blood vessel moving blood from the right side of the heart to the lungs. This narrowing can be due to many causes, including infection during pregnancy, a congenital heart defect, a problem with blood clotting in childhood or early adulthood, or a genetic change.
(HES7) or bHLHb37 is protein coding mammalian gene found on chromosome 17 in humans. HES7 is a member of the Hairy and Enhancer of Split families of Basic helix-loop-helix proteins. The gene product is a transcription factor and is expressed cyclically in the presomitic mesoderm as part of the Notch signalling pathway. HES7 is involved in the segmentation of somites from the presomitic mesoderm in vertebrates. The HES7 gene is self-regulated by a negative feedback loop in which the gene product can bind to its own promoter. This causes the gene to be expressed in an oscillatory manner. The HES7 protein also represses expression of Lunatic Fringe (LFNG) thereby both directly and indirectly regulating the Notch signalling pathway. Mutations in HES7 can result in deformities of the spine, ribs and heart. Spondylocostal dysostosis is a common disease caused by mutations in the HES7 gene. The inheritance pattern of Spondylocostal dysostosis is autosomal recessive.
Left-right asymmetry is the process in early embryonic development that breaks the normal symmetry in the bilateral embryo. In vertebrates, left-right asymmetry is established early in development at a structure called the left-right organizer and leads to activation of different signalling pathways on the left and right of the embryo. This in turn cause several organs in adults to develop LR asymmetry, such as the tilt of the heart, the different number lung lobes on each side of the body and the position of the stomach and spleen on the right side of the body. If this process does not occur correctly in humans it can result in the syndromes heterotaxy or situs inversus.
Isolated levocardia is a rare type of organs' situs inversus in which the heart is still in normal position but other abdominal viscera are transposed. Isolated levocardia may occur with heart defects and patients without having operations have low life expectancy: only about 5% to 13% of patients survive more than 5 years. Therefore, even though the risk of cardiac surgeries is high, once patients are diagnosed, operations are suggested to be held as soon as possible. Isolated levocardia is congenital. So far, there is not sufficient evidence to prove that chromosome abnormalities will result in isolated levocardia, and the cause of isolated levocardia is still unknown.
Manes Kartagener was a Swiss internist of Polish-Jewish origins.