What Is Situs Inversus

Overview 

Situs Inversus is an extremely rare syndrome present from birth. Estimated at an overall frequency of 1/10,000 births,¹ this condition is rarely seen in common clinical practice. It is characterised by complete and mirrored ‘transposition’ of the organs of both the abdomen (tummy) and chest onto the other side of the body.² In other words, all organs that are usually on the right are on the left, and all organs that are on the left are on the right. This syndrome is more commonly seen in assigned males at birth and occurs as the fetus develops within the womb.² Attributed to over 100 genes,² situs inversus can cause a number of problems, with some requiring surgical intervention. 

Understanding situs inversus 

As briefly discussed, situs inversus refers to the complete mirroring of the organs on the opposite side of the body. With ‘inversus’ meaning ‘inverted’, we can see how the condition refers simply to the inversion of the key organs. Whereas the heart is usually found on the left-hand side, in patients with situs inversus, it is typically found on their right. Similarly, the liver will be found on the left, whereas it is usually situated on the right. The displacement of organs onto the other side of the body can pose some challenges to healthcare professionals seeking to undertake some diagnostic tests.²  

A number of risk factors predisposing to the development of situs inversus have been established, including:²

• Family history of heart defects 
• Family history of non-cardiac-related anomalies
• Maternal diabetes
• Use of medications to treat a cough 
• Paternal smoking
• Low socioeconomic background

It was established that these risk factors appeared to have some connection with the genetic mutations associated with situs inversus.² Numerous genetic mutations have been identified in situs inversus, with these mutations causing abnormalities in the progression of embryo development. Abnormalities in signalling pathways controlled by serotonin have been identified as a potential cause of situs inversus, with abnormalities in genes controlling which side organs develop also identified.² Genes that have been ‘deleted’, such as the KIF3-A and KIF3-B genes, have also been identified to play a role in the development of situs inversus.²

Types and diagnosis of situs inversus 

Whilst situs inversus refers to the complete and total mirroring of organs onto the other side of the body, there are other types of ‘situs’ classifications established: 

1. Situs solitus²
   1. This refers to the normal positioning of the organs within the body. This means that all organs will be found where they should be expected to be found. 
2. Situs ambiguous³
   1. This refers to any abnormal distribution of the organs on both the left and right sides. Compared to situs inversus, however, there is no complete mirroring of all organs, meaning only the heart or liver could be on the opposite side. 
   2. Situs ambiguous is associated with higher mortality compared to situs inversus due to complications arising from the irregular asymmetry of organ distribution. 

Additionally, there are sub-classifications of situs inversus, which include:⁴

1. Dextrocardia with situs inversus:
   1. This is where the tip (apex) of the heart is also pointing towards the right side of the chest, reflecting a total mirroring of the organs. 
2. Levocardia with situs inversus:
   1. This is where the apex of the heart is pointing towards the left side of the chest (as is expected in normal positionings) whilst the other organs are on the opposite side. 
   2. This is a rarer form of situs inversus and is associated with a higher incidence of cardiac abnormalities. 

Diagnosing situs inversus 

Situs inversus can be diagnosed through a physical examination conducted by your healthcare provider. Clues towards a diagnosis of situs inversus may include not hearing or feeling a heartbeat on the left-hand side and instead hearing/feeling it on the right-hand side. Despite this, advancements in medical imaging have ensured earlier and easier detection of situs inversus. The imaging techniques commonly used to identify situs inversus include:²

• Ultrasound 
• X-Ray

There are many typical findings associated with these imaging techniques that often lead to a diagnosis of situs inversus. The most common details amongst healthcare professionals include:² 

• Dextrocardia (where the heart is on the opposite side of the chest compared to where it is normally found) 
• Left-placed liver
• Right-placed spleen (rarely, multiple spleens have been detected)

Additional imaging techniques can be used to better visualise the anatomy of the patient. These include: 

• CT 
• MRI 
• SPECT/CT with a specific marker for red blood cells (this can be used to distinguish the presence of multiple spleens from abdominal masses) 

Complications and implications of situs inversus 

Situs Inversus can cause an array of complications. The most common of these complications is one known as primary ciliary dyskinesia (PCD). This refers to an abnormality with the small hair-like structures that line many aspects of the body.⁵ When functioning correctly, the cilia ‘beat’ to move mucus and bacteria towards the mouth so that they can be expelled either via coughing or sneezing.⁵ When defective, mucus can build up in the lungs, causing bronchitis and pneumonia.⁵ Sinusitis is also another common symptom amongst those with situs inversus and PCD. 

The rate of congenital (present from birth) heart disease associated with situs inversus is approximately 3-9%.² These can include issues and defects with one of the main vessels of the heart, the inferior vena cava.² Kartagener Syndrome is a combination of both dextrocardia and PCD, with symptoms such as difficulty breathing, recurrent infections, clubbed fingers and blueish discolouration of the skin common to this syndrome.⁶ In situs ambiguus, these complications are far more numerous, with 80% of patients with this syndrome presenting with complex cardiac complications.²

Treating situs inversus 

Many patients with situs inversus may not know they have the syndrome and often lead lives without significant complications. Often, the diagnosis is made incidental to investigations looking at the cause for other illnesses. However, situs inversus does pose a challenge when patients potentially require surgical intervention. When requiring surgery, surgeons first have to understand the mirrored anatomy, often challenging common approaches significantly. This challenge is particularly pertinent when considering the need for an organ transplant. Due to the rarity of situs inverus, it can be challenging to locate organs that match the unique anatomical needs of a patient with situs inversus.² It is, therefore, important that your healthcare provider/s are made aware of your diagnosis so that prior arrangements can be made in the event of an emergency. 

Conclusion

Situs Inversus refers to the complete and total mirroring of the key organs onto the opposite side of the body compared to where they are usually located. When this occurs, patients can expect to find their heart located on their right, whereas it should usually be located on their left. There are other variations of ‘situs’ defined, including ‘situs ambiguus’, which refers to the uneven distribution of the organs on abnormal sides, and ‘situs solitus’, which refers to the normal distribution of organs. Diagnosis can typically be made following a physical examination conducted by your healthcare provider, although imaging techniques such as X-ray and ultrasound are typically used. To better visualise the anatomy of a patient with situs inversus, additional imaging techniques such as an MRI or CT can be utilized. Situs Inversus can cause significant complications, although the incidence of complications is far less common compared to situs ambiguus. Notably, situs inversus can cause issues with the cilia and heart, with defects in both resulting in Kartagener Syndrome. With this syndrome, patients can expect to experience respiratory symptoms such as breathlessness and recurrent infections and cardiac symptoms such as skin discolouration and finger clubbing. Whilst Situs Inversus does not need definitive treatment, it is important that your healthcare providers are aware of your diagnosis. This will allow them to put adequate preparations in place if an emergency arises and surgical intervention is necessitated. 

FAQs

Can I prevent situs inversus? 

Whilst numerous risk factors predisposing to the development of situs inversus have been identified, it is a genetic condition. This means that the condition can not be prevented, although it is key to remember that situs inversus is usually a condition without significant influence on mortality. 

What is the life expectancy of someone with situs inversus? 

Most people with situs inversus will lead an entirely normal life with the condition. It may be that you do not know you have the condition until it is incidentally identified by your healthcare professional. Compared to the other classifications of ‘situs’, situs inversus has a lower incidence of complications, meaning you can live without complications arising from the condition.