Situs inversus

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.

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.

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.

Axial CT image showing dextrocardia and situs inversus in a patient with Kartagener syndrome.

Axial CT image showing situs inversus (liver and IVC on the left, spleen and aorta on the right) in a patient with Kartagener syndrome.

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 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.

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 for situs inversus 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 patients, with medical professionals instead treating any other symptoms the patient may have with awareness of the unique anatomy of the patient.

Situs inversus is very rare, affecting 0.01% of the population.[8] This is equivalent to 1 in 10,000 people.[8]

Dextrocardia (the heart being located on the right side of the thorax) was seen and drawn by Leonardo da Vinci, 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:

• Enrique Iglesias, a Spanish singer, songwriter, actor and record producer.[9]
• Catherine O'Hara, Canadian-American actress, writer and comedian.[10]
• Randy Foye, an American basketball player in the NBA. He has suffered no discernible complications, and the condition is not expected to affect his career as a professional athlete, as all his organs are in reverse.[11]
• Ginggaew Lorsoongnern, a Thai convict executed by firing squad. Her condition was discovered after she was shot in the left side of her chest and survived. After waking up in the morgue she was taken back and executed.[12]
• Tim Miller, director of the Ashtanga Yoga Center in Carlsbad, California.[13]
• Rose Marie Bentley, a Molalla, Oregon woman who unknowingly had the rare variant situs inversus with levocardia, and lived to 99 years without any complications. She donated her body to Oregon Health & Science University, where her condition was discovered during an anatomy class after students noticed the unusual arrangement of her heart's blood vessels, prompting further investigation of the cadaver.[14][15]

• Ectopia cordis
• Asplenia
• Polysplenia
• Chirality (mathematics)
• Johann Friedrich Meckel, the Elder

• 00698 at CHORUS

• Chest X-ray & CT scan Radiology Teaching File