Situs inversus is a genetic condition that causes the organs in the chest and abdomen to be 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, and vice-versa. In the abdominal cavity, the liver is positioned predominantly on the left side instead of the right, and the stomach is on the right side instead of the left.
While these are some common presentations of situs inversus, others exist.
Situs inversus is a very rare condition. It occurs in 0.01 percent of the U.S. population, or in an estimated 1 in 10,000 people, according to Medscape (2013).
Situs inversus is caused by an autosomal recessive genetic condition. An unaffected carrier mother and an unaffected carrier father have a one in four chance of having a child with situs inversus. Because many genetic steps would have to come together to produce a child with situs inversus, the condition is rare.
The condition is also seen in “mirror image” twins. This is when the fertilized embryo splits later than is typical for twins. Mirror image twins can also be opposites of each other in terms of handedness, asymmetrical features, and/or brain-hemisphere dominance.
Situs inversus has two 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 remaining organs are flipped.
Levocardia is a rarer occurrence and is often associated with other cardiac abnormalities (Sharma, S., et al., 2012).
Another subtype is situs ambiguous, where several organs are in abnormal positions, but not in an easily defined pattern.
Because the organs can be functional for the most part in situs inversus, it is possible for a person to have no complications. However, 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. Individuals with situs inversus and PCD are said to have Kartagener syndrome. An estimated 20 percent of people with situs inversus have Kartagener syndrome (Medscape, 2013).
A physician can diagnose situs inversus by viewing the internal organs via X-ray, computed tomography (CT) scan, magnetic resonance imaging (MRI) scan, or an ultrasonography. Because the condition rarely causes symptoms and is so rare, a person may have come in for an entirely 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 apex or lower point of the heart on a person’s left side. However, a person with situs inversus can have a heart whose apex points to the right. In this case, the heartbeat would be loudest on the right side.
Physicians can use imaging studies to determine the exact type of situs inversus type.
For many patients, situs inversus is an abnormality that does not cause any other symptoms. They can live normal, healthy lives without any complications.
If a person is diagnosed with situs inversus and has other complications, such as a heart defect, a doctor will treat the patient’s symptoms. Surgery to reverse the organ’s positioning is usually not recommended.
Situs inversus is important to be aware of if a patient undergoes a surgical procedure.