Situs Inversus

Situs inversus (pronounced “SYE-tus in-VER-sus”) is a rare genetic condition where the major organs in your chest and abdomen form a mirror image of normal anatomy. Organs that are typically on the left side of your body are on the right. Organs that are typically on the right side of your body are on the left. The word “situs” refers to the position of your organs in your body. “Inversus” means reversed.

If you have normal anatomy, your organs follow a standard left-right pattern. This is called situs solitus. In situs inversus, this pattern is flipped. It’s like your body is reflected in a mirror. Despite this reversal, your organs usually develop and work properly. Situs inversus affects about 1 in every 10,000 people.

Most of the time, situs inversus is harmless. But the condition sometimes links to other genetic disorders and defects. Even if you don’t have symptoms, it’s important to let your healthcare providers know about the condition. They’ll want to monitor you for complications and prevent delays in future diagnoses and treatment.

What organs are on your left side?

In typical anatomy, organs on the left side of your body include:

• Heart
• Stomach
• Spleen
• Left lung (with two lobes)

What organs are on your right side?

In typical anatomy, organs on the right side of your body include:

• Liver
• Gallbladder
• Right lung (with three lobes)
• Appendix

How is this different in situs inversus?

In situs inversus, your organ positions are reversed. Your:

• Heart may be on the right side of your chest
• Liver and gallbladder may be on the left side of your abdomen
• Stomach and spleen may be on your right side
• Lung with three lobes may be on your left, and your two-lobed lung may be on your right

What are the different types of situs inversus?

Healthcare providers use the word “situs” to describe how your organs sit inside your body. They often use these terms together, which can be confusing. It helps to separate them into two categories: overall organ arrangement and heart position.

Overall organ arrangement

Most people are born with situs solitus. This is the typical arrangement of organs in your chest and abdomen. Other organ arrangements are:

• Situs inversus or situs inversus totalis: This means your organs are arranged in a complete mirror image of typical anatomy. Organs on the right side are on your left, and organs on the left side are on your right.
• Situs ambiguous: Providers use this term when organ placement doesn’t follow a clear or consistent pattern. Some organs may be reversed, and others aren’t.

Heart position

Providers describe the position of your heart separately from the arrangement of your other organs. Heart positions include:

• Dextrocardia: The tip of your heart (apex) points toward the right side of your chest. Dextrocardia often occurs with situs inversus, but it can also happen on its own.
• Levocardia: The tip of your heart points toward the left side of your chest, which is typical. When levocardia occurs with situs inversus, your heart is on your left side but your other organs are reversed.

What are the symptoms of situs inversus?

Most people with situs inversus have no symptoms. You may not realize you have it until you’re getting imaging tests for an unrelated reason.

When symptoms do occur, related conditions or defects usually cause them — not the organ reversal itself. These symptoms may include:

• Frequent sinus or lung infections
• Long-term (chronic) cough or breathing problems
• Heart-related symptoms, like weak pulse and pounding heartbeat

What causes situs inversus?

Situs inversus develops early in pregnancy, when a fetus’s organs are forming and taking their left-right positions. Normally, your body follows a precise pattern that places organs on specific sides.

In situs inversus, this left-right patterning is reversed. Researchers believe changes in certain genes disrupt left-right body development. They’ve linked more than 100 genes to defects related to sidedness in your body.

Situs inversus follows an autosomal recessive inheritance pattern. That means a child has to inherit a changed gene from both biological parents to get the condition.

Risk factors

You’re more likely to develop situs inversus if you have a biological family history of heart defects or noncardiac abnormalities. Your baby’s risk goes up if you:

• Have diabetes
• Use cough suppressants during pregnancy
• Smoke during pregnancy

Complications of this condition

Situs inversus can cause complications and is sometimes related to other conditions and defects. These include:

• Primary ciliary dyskinesia (PCD): PCD is a rare genetic disorder that affects tiny, hairlike structures called cilia. About half of PCD cases occur in people with situs inversus. This is called Kartagener syndrome.
• Congenital heart defects: Your heart may be reversed (dextrocardia) or have other structural abnormalities. Some defects may require surgery early in life.
• Delayed diagnosis of common conditions: Pain may appear on the “wrong” side. For example, your provider may rule out appendicitis if you have pain in your lower left side. (Pain appears in the lower right side in normal anatomy.)
• Surgical challenges: Healthcare providers need to consider how your reversed organ positions may affect imaging, procedures and surgeries. They may need time to make special plans.

How doctors diagnose this condition

Since most people don’t have symptoms, your healthcare provider may discover situs inversus while treating you for another reason.

They may notice the condition when they listen to your heartbeat. In typical anatomy, your heartbeat is usually loudest on the left side of your chest at the lowest point of your heart. If you have situs inversus, your heart points toward the right, and your heart beats the loudest on that side.

Your provider may use imaging tests to confirm the diagnosis. These tests can also help them figure out which organs are affected. These tests may include:

• Chest X-ray
• Abdominal ultrasound
• CT scan
• MRI scan

How is situs inversus treated?

Since it usually doesn’t cause any health problems, situs inversus itself doesn’t need treatment. Your provider will focus on any related conditions. Management for PCD may require:

• Airway clearance techniques, like huff coughing
• Antibiotics for infections
• Regular lung monitoring

Your provider will manage congenital heart defects and other organ-related issues on a case-by-case basis. Some defects may need surgery.

Although you may not need treatment, it’s important to let your healthcare providers know you have situs inversus. That’s because mirrored anatomy can make future health conditions harder to diagnose. Your providers should also know about your condition before they perform any kind of surgery or procedure.

What is the life expectancy of someone with situs inversus?

Most people with situs inversus live normal lives without any special treatment. You may not experience any symptoms or complications. So, you may not even know you have the condition.

But related conditions or defects can affect your overall health and life expectancy. Your outlook depends on your diagnosis and treatment. Knowing about reversed organs lets your healthcare provider monitor you for complications and start any necessary treatment early.