Situs Inverus – A Rare medical challenge

Definition

Situs inversus is a condition in which the organs of the chest and abdomen are arranged in a perfect mirror image reversal of the normal positioning.

Description

Normal human development results in an asymmetrical arrangement of the organs within the chest and abdomen. Typically, the heart lies on the left side of the body (levocardia), the liver and spleen lie on the right, and the lung on the left has two lobes while the lung on the right has three lobes. This normal arrangement is known as situs solitus.
However, in about 1 in 8,500 people, the organs of the chest and abdomen are arranged in the exact opposite position: the heart is on the right (dextrocardia), as is the two-lobed lung, and the liver, spleen, and three-lobed lung are on the left. Yet because this arrangement, called situs inversus, is a perfect mirror image, the relationship between the organs is not changed, so functional problems rarely occur.

Causes and Symptoms

Early in the normal development of an embryo, the tube-like structure that becomes the heart forms a loop toward the left, identifying the left/right axis along which the other organs should be positioned. Although the mechanism that causes the heart loop to go left is not fully understood, at least one gene has been identified to have a role in this process. However, it is thought that many factors may be involved in causing situs inversus. Rarely, situs inversus can run in families, but most often it is an isolated and accidental event occurring in an individual for the first time in the family.
Most people with situs inversus have no medical symptoms or complications resulting from the condition. Although only 3-5% of people with situs inversus have any type of functional heart defect, this is higher than the rate of heart defects in the general population, which is less than 1%.
It is estimated that about 25% of people with situs inversus have an underlying condition called primary ciliary dyskinesia (PCD). PCD, also known as Kartagener’s syndrome, is characterized as situs inversus, chronic sinus infections, increased mucous secretions from the lungs, and increased susceptibility to respiratory infections. PCD is caused by a defect in the cilia that impairs their normal movements.

Diagnosis

Situs inversus should detected by a thorough physical examination. It is often picked up when a physician, using a stethoscope, hears otherwise normal heart sounds on the right side of the body instead of the left. To confirm the a suspected diagnosis of situs inversus, imaging studies such as MRI, CT, or ultrasound may be ordered, and a referral may be made to a cardiologist or internist for completeness. Imaging studies will also rule out the possibility of random arrangement of the organs, or heterotaxy, which has a much higher risk for serious medical complications.

Treatment

There is no treatment for situs inversus. In the unlikely case that a heart defect is present, it should be treated accordingly by a cardiologist.
Individuals who have situs inversus should be sure to inform all physicians involved in their medical care. In addition to preventing unnecessary confusion, this will reduce the risk of missing a crucial diagnosis that presents with location-specific symptoms (such as appendicitis).

Alternative Treatment

Not applicable.

Prognosis

The prognosis for an individual with situs inversus is good, and in the absence of a heart defect or other underlying diagnosis, life expectancy is normal.

Prevention

There is no known method of preventing situs inversus.

Significance

Situs inversus has an autosomal recessive pattern of inheritance.
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 left lower 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 should inform their physicians before an examination, so they may redirect their search for heart sounds and other signs.
Situs inversus also complicates organ transplantation operations as donor organs will almost certainly come from situs solitus 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

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.

Notable persons with situs inversus

Notable individuals with documented cases of situs inversus include:

• Randy Foye, an American basketball player for the NBA’s Minnesota Timberwolves. He has suffered no discernible complications, and the condition is not expected to jeopardize his career as a professional athlete.
• Catherine O’Hara, the Canadian comedic actress has said in interviews that her organs are reversed and her heart is on the right side of her chest.
• Donny Osmond, whose appendicitis was initially dismissed as a less serious condition because nobody realized he had situs inversus. It was discovered when he was taken to hospital when on tour with his family in England.
• Enrique Iglesias, the Spanish singer told the press that he was born with situs inversus.

Fictional characters with situs inversus

• In the Ian Fleming novel Dr. No, Julius No explains to James Bond that he once survived a murder attempt because his heart is located on his right side, which his would-be-killers did not know when they stabbed the spot on the left where the heart of a normal human being would be.
• Souther, from the anime/manga Fist of the North Star, has situs inversus totalis, making him immune to standard pressure-points martial arts.
• In the webcomic It’s Walky!, anyone who goes through the Martian resurrection process ends up being completely reversed, with their organs mirrored within their bodies and their primary hand becoming the opposite of what it had been before. This process happens to several major characters throughout the comic’s run.
• In the WB series Jack & Jill, Simon Rex played a young man with situs inversus.
• Fortune, from Metal Gear Solid 2: Sons of Liberty. Revolver Ocelot points this out when he shoots Fortune on the left side of her chest, then remembers and states that her heart was on the right side.
• In Margaret Mahy’s novel The Tricksters, the character Hadfield is said to be an exact mirror image of his otherwise identical twin Felix, including having his vital organs in mirror-image layout.
• In the Lord Peter Wimsey short story The Image in the Mirror by Dorothy Sayers, a character with reversed organs has long been haunted by dreams of a doppelgänger and by fears that he himself might be only the reflection of someone else.
• In the Max Brooks novel World War Z, a character describes operating on a patient who had dextrocardia with situs inversus, and transplants a heart from someone with the same condition. Unbeknownst to him, the transplant heart is infected with the virus Solanum, thus turning the patient into a zombie.

Sources

• Wikipedia
• Health At OZ

Filed under: Medical World, Situs Inverus - A Rare medical challenge