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Hi, my name is Jamie To and this is my project on Situs Inversus. So, Situs inversus, is defined as a congenital condition in which the major visceral organs are reversed or mirrored from their normal positions. The normal arrangement of internal organs is known as situs solitus. Although cardiac problems are more common, many people with situs inversus have no medical symptoms or complications resulting from the condition, and until modern medicine, it was usually undiagnosed. As you can see in this x-ray image, the internal organs of this patient are mirrored along the sagittal plane by which the heart is on the right side, the liver, left and the thoracic and abdominal organs are completely reversed. This is known as situs inversus totalis. 49

You may ask, why ‘totalis?’ This is because situs inversus like many other conditions has variations. However, this is the most typical variance. Affecting about 1 in ten thousand, situs inversus has a much more uncommon manifestation that affects the heart and other organs. These are known as isolated levocardia and situs ambiguous (otherwise known as heterotaxy, in which situs (or originating position) cannot be determined), respectfully. This condition, known as situs inversus with levocardia also known as situs inversus incompletus, affects about 1 in 2 million people. This condition itself does not cause complications, however oftentimes there are defects that come with it.

Situs ambiguous or the more fitting name heterotaxy, translated as “different arrangement” affects people on a spectrum. As you can see in this image, it shows the typical visceral arrangement on the left and situs inversus totalis on the right, variations in situs inversus such as right atrial isomerism syndrome and left atrial isomerism syndrome are shown between. In this case there is no spleen in right isomerism as opposed to several spleens in left isomerism. Sometimes these can present with complications in the intestines due to malrotation. Studies show that right isomerism may present with more heart defects than left isomerism, such as the transposition of great arteries and levocardia.

Transposition of the great arteries affects the five great vessels that carry blood to and from the heart. The superior (1) and inferior (2) vena cava bring blood from the body back to the heart. The pulmonary artery (3) takes the blood from the right ventricle to the lungs to become oxygenated. The pulmonary veins (4) bring the blood back to the heart from the lungs. And finally, the aorta, that carries oxygenated blood from the heart to the rest of the body. In this condition the aorta and the pulmonary artery have switched connections. The aorta is attached to the right ventricle instead of the left, and the reverse is true for the pulmonary artery. Meaning, the aorta receives deoxygenated blood from the superior vena cava and Inferior Vena Cava from the right atrium and pumps it right back out to the body. The pulmonary artery receives oxygenated blood from the Pulmonary Veins via the left atrium and pumps it right back to the lungs. This is usually found in babies in utero along with a second defect known as patent ductus arteriosus, in which there is a connection between the pulmonary artery and the aorta called the ductus arteriosus where some oxygenated blood can escape into the aorta and oxygenate the rest of the body, this is the only thing that keeps the patient alive. It is treated by injecting medicine that will keep the ductus open, early detection will increase chances of survival. Levocardia, however, is a congenital heart defect that accompanies the change of orientation. The valves of the heart may be misshaped so they don’t close completely, causing a heart murmur, or the muscle fibers may not align for efficient pumping. Neither of these problems allow for maximal blood flow through the body. Which decreases the chance of survival greatly.


So why does this occur? It has been found that this condition is an autosomal recessive genetic condition. However, the condition can be linked to the x chromosome and may still occur in identical mirror image twins. Studies show that about a quarter of people who situs inversus also have a ciliary dysfunction that takes place during embryonic development in which cilia are responsible with determining internal organ positioning, so embryos with this dysfunction are half as likely to have situs inversus. Scientists have not been able to study this condition more due to its rarity, and rather mysterious nature. Because the only way to diagnose this condition is through diagnostic imaging, it was widely undiagnosed and undetectable unless there are complications. Some interesting and notable cases of this condition include singer/songwriter Enrique Inglesias and Donny Osmond! Pretty neat! Thanks for listening, bye!

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