Which is not component of left isomerism?
**Core Concept**
Left isomerism, also known as situs ambiguus, is a rare congenital anomaly where the internal organs are reversed or mirrored from their typical positions. This condition can occur due to genetic mutations affecting the left-right axis determination during embryonic development.
**Why the Correct Answer is Right**
Left isomerism typically involves the presence of bilateral right-sidedness, where organs like the heart, lungs, and liver are positioned on the left side of the chest, and abdominal organs are on the right. The correct components of left isomerism include asplenia, polysplenia, and bilateral right-sidedness of the heart and liver. However, the correct answer is not a component of left isomerism.
**Why Each Wrong Option is Incorrect**
**Option A:** Asplenia is a component of left isomerism, where the spleen is either absent or rudimentary.
**Option B:** Polysplenia is another characteristic feature of left isomerism, where multiple small spleens are present.
**Option C:** Bilateral right-sidedness of the heart and liver is a hallmark of left isomerism, where the typical left-sided organs are found on the right side of the chest.
**Clinical Pearl / High-Yield Fact**
Left isomerism is often associated with a high risk of congenital heart defects, particularly total anomalous pulmonary venous return, and is typically diagnosed prenatally or in early childhood.
**Correct Answer:** D.