Asplenia syndrome, also known as right atrial isomerism is a subcategory of heterotaxy. It involves multiple malformations and abnormal location of organs, characteristically including congenital cardiac lesions and the absence of a spleen.
Asplenia syndrome (AS) is a condition that results from failure of normal rotation of thoracic and abdominal structures during embryogenesis. It is often detected soon after birth and constitutes 1% of newborns diagnosed with congenital heart disease. AS is a subtype of heterotaxy, also referred to as right atrial isomerism, and falls within a wide range of lateralization disorders that have variable abnormalities and presentations . In AS, the left side of the body is essentially a copy of the right-hand side, hence the characteristic absence of the spleen, which is normally located on the left. Although hereditary occurrences have been reported, some following an X-linked pattern, most cases of AS are isolated, and the etiology is unknown.
The common signs associated with AS are congenital cardiac malformations, which are often cyanotic and are the most frequent cause of symptoms and death. They usually consist of transposition of great vessels, pulmonary stenosis (and other valvular diseases), and total anomalous pulmonary venous connection (TAPVC).
Furthermore, AS is associated with numerous defects in the chest and abdominal cavities, the most prominent and clinically relevant of these being the lack of development of a spleen. Individuals with asplenia have a weakened immune system and are more susceptible to severe life-threatening infections, particularly those mediated by encapsulated organisms  . This risk exists throughout their entire lives. Other abnormalities reported include a midline or transverse liver, gall bladder and pancreas malformations, three lobes in both lungs, as well as an inferior vena cava that is located anterior to the aorta. AS carries a high mortality rate as over 85% of children born with AS die before the age of one year  . It is thought that those who survive beyond childhood may have milder manifestations and complications.
The diagnosis of AS depends on a combination of history, physical examination and imaging findings. Features known to be typical in AS are used to guide the choice of investigations, which focus on specific systems or organs. These may include: