Situs inversus describes the anatomical arrangement in which the organs of the chest and abdomen are positioned as a mirror-image reversal of the normal placement. Most individuals with this condition do not have clinical manifestations.
Most individuals with situs inversus will live normally without repercussions. In fact, the abnormal anatomy is typically recognized incidentally when patients receive testing for unrelated health issues.
In patients with Kartagener syndrome, defective cilia motility make it difficult to clear mucosal secretions, a manifestation that predisposes the patient to respiratory infections. Sinusitis is characterized by fever, cough, runny nose, headache, and facial pain.
In those with situs inversus, the location of specific diseases such as appendicitis and cholecystitis will present in different locations. The former will display symptoms in the lower left quadrant and the latter will appear in the upper left quadrant.
A majority of patients with situs inversus are diagnosed incidentally while undergoing workup for other underlying conditions while just a few cases may actually exhibit a clinical picture suggestive of this anomaly. For all patients suspected to have situs inversus and those with accidental findings, the assessment should include a personal and family history, a physical exam with special focus on the cardiovascular system and abdomen, and imaging studies.
There are numerous imaging techniques that can be performed with the CT scan considered to be the confirmatory examination. This imaging modality provides key anatomic information such as the position of the cardiac apex and other organs as well as the branches of the vessels .
Complicated cases with cardiac defects are evaluated with MRI .
Other useful tools are the echocardiogram, ultrasonography of abdominal organs, and radiography    .
Standard obstetrical ultrasonography is essential in the evaluation of the fetal anatomy. Hence, it will detect any lateralization abnormalities.
It is pertinent that the clinician and ultrasound technician are aware of any positive family history in order to thoroughly screen for this.
No treatment is indicated for situs inversus unless the patient has congenital heart disease and associated complications, in which the specific therapy will depend on the cardiac anomaly and the clinical picture.
In order to provide excellent care to these patients, the medical team should be informed about the patient's anatomy prior to diagnosing abdominal disease or performing any surgical procedure.
In patients with Kartagener syndrome, the bronchiectasis and sinusitis are managed and treated accordingly. For example, therapy should be directed at the facilitation of mucus clearance. Also, respiratory bacterial infections will require antibiotics.
When appearing as an isolated condition, situs inversus is associated with a good prognosis as patients are expected to live healthy lives with a normal life expectancy. If cardiac malformation is present, patients may be at an increased risk for morbidity and mortality depending on the specific type of heart defect. Additionally, congenital syndromes particularly featuring partial situs inversus may include anomalies of the midline axis, kidneys, and biliary structures.
Patients with Kartagener syndrome are susceptible to respiratory infections, which can lead to severe manifestations.
The etiology of this condition is not well elucidated but there are varied inheritance patterns observed across affected families. These mutations are most frequently present as an autosomal recessive trait although the disease has been transmitted through X-linked modes very rarely.
It is believed that the mutated genes responsible for this condition are present on chromosome 12. Specifically, these are the lefty genes, nodal genes as well as ZIC 3, ACVR2B and Pitxz genes    .
This lateralization defect occurs during embryogenesis when the tube structure that eventually develops into the heart loops in the reverse direction. The consequence is the organ displacement observed in situs inversus.
The incidence of situs inversus is estimated as approximately 1 in 8,000 to 1 in 25,000 live births .
A commonly associated disorder, Kartagener syndrome, is present in 20% of situs inversus cases. Moreover, situs inversus affects half of individuals with this syndrome .
The normal anatomic placement of the heart and abdominal organs is referred to as situs solitus . When the position of these visceral organs is inverted, this is defined as situs inversus. There are two main types of this condition which are classified according to the direction of the cardiac apical position at birth. Situs inversus with dextrocardia refers to an apical position displayed to the right while situs inversus with levocardia indicates that the apex is tilted to the left.
The arrangement of situs inversus is projected as a perfect mirror image. Therefore, the connection between the organs remains the same. As a result, they function normally.
Association with other disorders
Situs inversus may exist as an isolated disease but it can also present along with bronchiectasis and sinusitis to form the clinical triad typically observed in Kartagener syndrome. The latter is a result of a ciliary dysfunction. Normally, cilia in a region of the embrio called the node play a key role in establishing a left-right symmetry by producing a gradient in embryonic fluid. As one study reported, the immobility of nodal cilia may be responsible for the development of situs inversus .
Situs inversus is not preventable since it is the result of a genetic disorder.
Patients and unaffected family members may seek counseling to gain an understanding of the condition, what it entails, its possible complications, the possible modes of transmission, and other important details.
Note that clinicians treating individuals with situs inversus should be aware of its presence to avoid any confusion associated with location-dependent differential diagnoses.
Situs inversus refers to a rare condition, in which the thoracic and abdominal organs are positioned as a mirror image of the normal anatomy. Specifically, the term situs is defined as the position of the atrial chambers and the visceral organs   whereas inversus describes the reversal of the chest and abdominal organs. Furthermore, this condition is classified into two types which are situs inversus with dextrocardia and situs inversus with levocardia with each representing the particular direction of the cardiac apex. Additionally, situs inversus encompasses various possibilities of disorders depending on whether the inversion applies to all organs or some.
This anatomic defect is caused by malrotation of the heart tube during fetal development. It occurs as a result of genetic mutations, which are often inherited through an autosomal recessive mode.
Individuals with situs inversus are asymptomatic unless they have congenital heart defects or other underlying diseases. Additionally, situs inversus is commonly found in patients with Kartagener syndrome or primary ciliary dyskinesia (PCD).
In most patients, situs inversus is identified coincidentally while undergoing investigative studies for other conditions. The workup includes a full medical and family history, a physical exam, and imaging techniques. The latter includes effective diagnostic tools such as radiography, ultrasonography, computed tomography (CT) scan, and magnetic resonance imaging (MRI).
Individuals without clinical manifestations don't warrant treatment. If concurrent congenital anomalies or other diseases are present, then these will require an appropriate management. Note that all clinicians providing care for the patient in all settings should be aware of the presence of situs inversus.
What is situs inversus?
Situs inversus is a condition in which the heart, lungs, and abdominal organs are reversed in a manner that is a mirror image of what the normal anatomy should appear as. For example, the heart is on the right side of the chest instead of the left. The right and left lungs are switched. The stomach, spleen, liver, and appendix may also be on opposite sides depending on whether the reversal includes all organs or just some.
What causes this condition?
The causes are not fully known but it is understood that there are abnormalities that occur during the fetal development.
Situs inversus is a genetic disease that is inherited in different ways. Most patients inherit this condition through an autosomal recessive pattern. This means that the patient must have two defective genes, thus receiving a bad copy from each parent.
What are the signs and symptoms?
Fortunately, if the patient has no heart defects, then s/he will have no symptoms. However, if there are abnormal heart structures, then the individual will experience complications due to those.
Also, it is important to note that 20% of patients with situs inversus will have Kartagener syndrome, which is a disease that makes it difficult for patients to clear their mucus secretions, which increases the risk of developing respiratory infections such as sinusitis. Symptoms of sinusitis include fever, cough, facial pain, congestion, etc.
How is situs inversus diagnosed?
Most of the patients will be diagnosed with situs inversus accidentally as part of a workup for something else.
There are numerous imaging tests that will diagnose situs inversus including:
Note that during the obstetric ultrasound, the clinician can detect situs inversus during the examination of the fetal anatomy. The parents will be made aware of the condition.
How is it treated?
When situs inversus exists by itself, there is no required treatment. When it appears with heart anomalies, the patients may require surgery and management of these anomalies.
Are there any special considerations?
The medical team should be aware of patients with situs inversus in order to provide excellent care to the patient.
What is the prognosis?
Again, if situs inversus is alone, there are no health issues. Patients live healthy lives and have a normal life expectancy.
Can it be prevented?
Since this is a genetic disorder, it cannot be prevented. Affected individuals and their family members can seek prenatal counseling to learn about the condition and how it is transmitted to future children.
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