What is situs inversus?

Situs inversus is a genetic condition in which the organs in the chest and abdomen are positioned in a mirror image from their normal positions. For example, the left atrium of the heart and the left lung are positioned on the body’s right side. In the abdominal cavity, the liver is positioned mostly on the left side instead of the right. And the stomach is on the right side of the body instead of the left.

Situs inversus is a very rare condition. According to an article in the journal Heart Views, it occurs in an estimated 1 in 10,000 people.

Situs inversus is caused by an autosomal recessive genetic condition. An unaffected carrier mother and an unaffected carrier father have a 1 in 4 chance of having a child with situs inversus. Because many genetic steps would have to come together to cause situs inversus, the condition is rare.

The condition is also seen in “mirror image” twins. This type of twins occurs when a fertilized embryo splits later than usual during pregnancy. Mirror image twins can also be opposites in things like handedness, asymmetrical features, and brain-hemisphere dominance.

Situs inversus has two main subtypes: dextrocardia and levocardia. A person is said to have dextrocardia if the point of the heart is on the right side. A person is said to have levocardia if the heart is on the left side, yet the other organs are flipped.

Levocardia is rarer and often associated with other cardiac abnormalities, according to an article in the Journal of Anatomy & Physiology.

Another subtype is situs ambiguous. This occurs when several organs are in abnormal positions, but not in an easily defined pattern.

Because the organs can be functional in situs inversus, it’s possible for a person to have no complications.

Other patients can experience cardiac dysfunction or a lung condition called primary ciliary dyskinesia (PCD), which causes mucus buildup in the lungs. This can lead to chronic bronchitis and sinusitis. People with situs inversus and PCD are said to have Kartagener’s syndrome.

A doctor can diagnose situs inversus by looking at the organs via:

  • X-ray
  • CT scan
  • MRI scan
  • ultrasonography

Because the condition seldom causes symptoms and is so rare, a person may not know they have it. And it may not be discovered until visiting a doctor for a different reason.

Another way situs inversus may be discovered is when a doctor listens to a patient’s heartbeat. The heartbeat is typically loudest at the lower point of the heart on a person’s left side.

But a person with situs inversus can have a heart that points to the right, so the heartbeat would be loudest on that side.

Doctors can use imaging studies to determine the exact type of situs inversus.

For many patients, situs inversus doesn’t cause any other symptoms. If a person with situs inversus does have complications like a heart defect, a doctor will treat the symptoms. Surgery to reverse the organs’ positioning is usually not recommended.

Knowing if you have situs inversus is important if you undergo another surgical procedure.

Situs inversus is a very rare birth defect in which some organs are atypically placed. Sometimes there are no symptoms, and in other cases, there are associated complications.

Often, the condition is discovered when the patient visits a doctor for completely different medical care. Treatment is usually aimed at helping symptoms of a related complication like a heart defect. Surgery to correct the organs’ positioning is usually not recommended.