Situs inversus
Encyclopedia
Situs inversus is a 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.
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 seen and drawn by Leonardo da Vinci
in 1452–1519, and then recognised by Marco Aurelio Severino
in 1643. However, situs inversus 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.
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 vessel
s, nerve
s, lymphatics and the intestine
s 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 in the normal left side of the thorax, a much rarer condition (1 in 22,000 of the general population), it is known as situs inversus with levocardia
or situs inversus incompletus. Situs inversus with levocardia, or dextrocardia without situs inversus, present much higher rates of congenital defects than situs inversus with dextrocardia.
Situs inversus is generally an autosomal recessive genetic
condition, although it can be X-linked or found in identical "mirror" twins
.
In the absence of congenital heart defects, individuals with situs inversus are phenotypically
unimpaired, and can lead normal 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.
Many people with situs inversus totalis are unaware of their unusual anatomy until they seek medical attention for an unrelated condition. The reversal of the organs may then lead to some confusion, as many signs and symptoms will be on the 'wrong' 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. Thus, in the event of a medical problem, the knowledge that the individual has situs inversus can expedite diagnosis. People with this rare condition may inform their physician
s before an examination, so the physician can redirect their search for heart sounds and other signs. Wearing a medical identification tag
can help to inform health care providers in the event the person is unable to communicate.
Situs inversus also complicates organ transplantation operations as donor organs will almost certainly 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 with situs inversus who requires a heart transplant needs all the vessels to the transplant donor heart reattached to their existing ones. 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 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.
Congenital disorder
A congenital disorder, or congenital disease, is a condition existing at birth and often before birth, or that develops during the first month of life , regardless of causation...
in which the major visceral organs
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
are reversed or mirrored
Mirror image
A mirror image is a reflected duplication of an object that appears identical but reversed. As an optical effect it results from reflection off of substances such as a mirror or water. It is also a concept in geometry and can be used as a conceptualization process for 3-D structures...
from their normal positions. The normal arrangement is known as situs solitus
Situs solitus
Situs solitus refers 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...
. In other rare cases, in a condition known as situs ambiguus
Situs ambiguus
Situs ambiguus or situs ambiguous , also known as heterotaxy, is a rare congenital defect in which the major visceral organs are distributed abnormally within the chest and abdomen.The normal position of the organs is known as situs solitus; situs inversus is a condition in which the usual...
or heterotaxy, situs cannot be determined.
The term situs inversus is a short form of the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
phrase "situs inversus viscerum", meaning "inverted position of the internal organs". Dextrocardia
Dextrocardia
Dextrocardia is a congenital defect in which the heart is situated on the right side of the body. There are two main types of dextrocardia: dextrocardia of embryonic arrest and dextrocardia situs inversus...
(the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
being located on the right side of the thorax
Thoracic cavity
The thoracic cavity is the chamber of the human body that is protected by the thoracic wall ....
) was first seen and drawn by Leonardo da Vinci
Leonardo da Vinci
Leonardo di ser Piero da Vinci was an Italian Renaissance polymath: painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist and writer whose genius, perhaps more than that of any other figure, epitomized the Renaissance...
in 1452–1519, and then recognised by Marco Aurelio Severino
Marco Aurelio Severino
Marco Aurelio Severino was an Italian surgeon and anatomist.-Biography:Severino was born in Tarsia , of Giovanni Jacopo Severino, a lawyer. He died of plague in 1656....
in 1643. However, situs inversus was first described more than a century later by Matthew Baillie
Matthew Baillie
Matthew Baillie was a Scottish physician and pathologist.-Life:...
.
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 thoraxThoracic cavity
The thoracic cavity is the chamber of the human body that is protected by the thoracic wall ....
and abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
. Generally, the organs are simply transposed through the sagittal plane
Sagittal plane
Sagittal plane is a vertical plane which passes from front to rear dividing the body into right and left sections.-Variations:Examples include:...
. The heart is located on the right side of the thorax, the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
and spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
on the right side of the abdomen and the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and gall bladder on the left side. The left lung is trilobed and the right lung bilobed, and blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s, nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s, lymphatics and the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s are also transposed.
If the heart is swapped to the right side of the thorax, it is known as situs inversus with dextrocardia
Dextrocardia
Dextrocardia is a congenital defect in which the heart is situated on the right side of the body. There are two main types of dextrocardia: dextrocardia of embryonic arrest and dextrocardia situs inversus...
or situs inversus totalis. If the heart remains in the normal left side of the thorax, a much rarer condition (1 in 22,000 of the general population), it is known as situs inversus with levocardia
Levocardia
Levocardia is a medical condition where the heart is on the correct side of the body , but the related structures are on the wrong side, either due to corrected transposition of the great vessels or to situs inversus....
or situs inversus incompletus. Situs inversus with levocardia, or dextrocardia without situs inversus, present much higher rates of congenital defects than situs inversus with dextrocardia.
Significance
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
condition, although it can be X-linked or found in identical "mirror" twins
TWINS
Two Wide-Angle Imaging Neutral-Atom Spectrometers are a pair of NASA instruments aboard two United States National Reconnaissance Office satellites in Molniya orbits. TWINS was designed to provide stereo images of the Earth's ring current. The first instrument, TWINS-1, was launched aboard USA-184...
.
In the absence of congenital heart defects, individuals with situs inversus are phenotypically
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
unimpaired, and can lead normal 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
Transposition of the great vessels
Transposition of the great vessels is a group of congenital heart defects involving an abnormal spatial arrangement of any of the primary blood vessels: superior and/or inferior vena cavae , pulmonary artery, pulmonary veins, and aorta...
. The incidence of congenital heart disease is 95% in situs inversus with levocardia.
Many people with situs inversus totalis are unaware of their unusual anatomy until they seek medical attention for an unrelated condition. The reversal of the organs may then lead to some confusion, as many signs and symptoms will be on the 'wrong' side. For example, if an individual with situs inversus develops appendicitis
Appendicitis
Appendicitis is a condition characterized by inflammation of the appendix. It is classified as a medical emergency and many cases require removal of the inflamed appendix, either by laparotomy or laparoscopy. Untreated, mortality is high, mainly because of the risk of rupture leading to...
, they will present to the physician with lower left abdominal pain, since that is where their appendix lies. Thus, in the event of a medical problem, the knowledge that the individual has situs inversus can expedite diagnosis. People with this rare condition may inform their physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
s before an examination, so the physician can redirect their search for heart sounds and other signs. Wearing a medical identification tag
Medical identification tag
A medical identification tag is a small emblem or tag worn on a bracelet, neck chain, or on the clothing bearing a message that the wearer has an important medical condition that might require immediate attention...
can help to inform health care providers in the event the person is unable to communicate.
Situs inversus also complicates organ transplantation operations as donor organs will almost certainly 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 with situs inversus who requires a heart transplant needs all the vessels to the transplant donor heart reattached to their existing ones. However, the orientation of these vessels in a person with situs inversus is reversed, necessitating steps so that the blood vessels join properly.
Kartagener syndrome
Primary ciliary dyskinesia
Primary ciliary dyskinesia , also known as immotile ciliary syndrome or Kartagener Syndrome ', is a rare, ciliopathic, autosomal recessive genetic disorder that causes a defect in the action of the cilia lining the respiratory tract and fallopian tube, and also of the flagella of sperm in...
(PCD). PCD is a dysfunction of the cilia
Cilium
A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....
that manifests itself during the embryologic phase of development. Normally-functioning cilia determine the position of the internal organs during early embryological development
Mammalian embryogenesis
Mammalian embryogenesis is the process of cell division and cellular differentiation during early prenatal development which leads to the development of a mammalian embryo.-Difference from human embryogenesis:...
, 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
Sinusitis
Sinusitis is inflammation of the paranasal sinuses, which may be due to infection, allergy, or autoimmune issues. Most cases are due to a viral infection and resolve over the course of 10 days...
, and bronchiectasis
Bronchiectasis
Bronchiectasis is a disease state defined by localized, irreversible dilation of part of the bronchial tree caused by destruction of the muscle and elastic tissue. It is classified as an obstructive lung disease, along with emphysema, bronchitis, asthma, and cystic fibrosis...
. Cilia are also responsible for clearing mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
from the lung, and the dysfunction causes increased susceptibility to lung infections.
Notable persons with situs inversus
Notable individuals with documented cases of situs inversus include:- Randy FoyeRandy FoyeRandy Foye is an American professional basketball player currently with the NBA's Los Angeles Clippers. He played collegiately at Villanova University. He was selected seventh overall in the 2006 NBA Draft by the Boston Celtics, immediately traded to the Portland Trail Blazers, and later traded to...
, an American basketballBasketballBasketball is a team sport in which two teams of five players try to score points by throwing or "shooting" a ball through the top of a basketball hoop while following a set of rules...
player in the NBA. He has suffered no discernible complications, and the condition is not expected to jeopardize his career as a professional athlete. - Catherine O'HaraCatherine O'HaraCatherine Anne O'Hara is a Canadian-American actress and comedienne. She is well known for her comedy work on SCTV, and her roles in the films After Hours, Beetlejuice, Home Alone, and The Nightmare Before Christmas, and also in the mockumentary films written and directed by Christopher Guest...
, the Canadian comedic actress, has said in interviews that her organs are reversed and her heart is on the right side of her chest.
See also
- Situs solitusSitus solitusSitus solitus refers 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...
- Situs ambiguusSitus ambiguusSitus ambiguus or situs ambiguous , also known as heterotaxy, is a rare congenital defect in which the major visceral organs are distributed abnormally within the chest and abdomen.The normal position of the organs is known as situs solitus; situs inversus is a condition in which the usual...
- Ectopia cordisEctopia cordisEctopia cordis is a birth defect in which the heart is abnormally located. In the most common form, the heart protrudes outside the chest through a split sternum...
- AspleniaAspleniaAsplenia refers to the absence of normal spleen function and is associated with some serious infection risks. Hyposplenism is used to describe reduced splenic functioning, but not as severely affected as with asplenism.-Congenital:...
- PolyspleniaPolysplenia-Associated conditions:There are frequent associated congenital anomalies all related to deviations in the development of anatomical asymmetries in early embryonic stages...
- Chirality (mathematics)Chirality (mathematics)In geometry, a figure is chiral if it is not identical to its mirror image, or, more precisely, if it cannot be mapped to its mirror image by rotations and translations alone. For example, a right shoe is different from a left shoe, and clockwise is different from counterclockwise.A chiral object...
- Johann Friedrich Meckel, the ElderJohann Friedrich Meckel, the ElderJohann Friedrich Meckel the Elder was a German anatomist who was born in Wetzlar. He often has "the Elder" appended to his name to avoid confusion with his famous grandson Johann Friedrich Meckel , who was also an anatomist and often has "the Younger" included with his name...