Most common organ involved by congenital TB is
First, I need to recall the core concept. Congenital tuberculosis is transmitted from mother to fetus, usually during the last trimester. The primary infection site in newborns is often the lymph nodes, especially the hilar lymph nodes. This is different from postnatal TB where the lungs are more commonly affected. So the core concept here is the anatomical predilection of congenital TB.
Next, explaining why the correct answer is right. Congenital TB occurs when the mother has active TB, and the bacteria cross the placenta. The fetus's immune system is immature, leading to a disseminated infection. The lymphatic system is a common site because the bacteria can spread through the bloodstream, and the lymph nodes are part of the first line of defense. Hilar lymph node involvement is typical, leading to symptoms like hepatosplenomegaly and generalized lymphadenopathy.
Now, the incorrect options. Let's say the options were liver, lungs, and others. The liver is involved in congenital TB but isn't the most common. The lungs are more associated with postnatal TB. Other organs like the brain might be involved in miliary TB but again, not the most common in congenital cases. Each incorrect option should be addressed briefly, explaining why they're less likely.
Clinical pearl: Remember that congenital TB presents differently from adult TB. The lymph nodes, especially hilar, are key in congenital cases. A mnemonic could be "Lymph nodes lead in congenital TB," helping students recall this point.
Finally, the correct answer is the lymph nodes. Make sure the explanation is concise and fits within the character limit. Check all sections are covered and formatted properly with bold labels. Avoid markdown except for bold. Keep sentences clear and precise for a postgraduate student.
**Core Concept**
Congenital tuberculosis (TB) results from transplacental transmission of *Mycobacterium tuberculosis* from an infected mother. The **lymphatic system**, particularly **hilar lymph nodes**, is the most frequently affected organ due to the immature immune response in neonates, which favors dissemination via the bloodstream.
**Why the Correct Answer is Right**
In congenital TB, the bacteria reach the fetus via the maternal bloodstream, seeding the **hilar lymph nodes** first. This is because neonates lack mature cell-mediated immunity, allowing *M. tuberculosis* to replicate unchecked in lymphoid tissues. The lymph nodes act as a primary reservoir, leading to systemic spread (e.g., hepatosplenomegaly, miliary disease). This contrasts with postnatal TB, where the lungs are the primary site.
**Why Each Wrong Option is Incorrect**
**Option A:** **Liver** – While the liver may be involved in disseminated congenital TB, it is not the *most common* site. Lymph nodes are more frequently affected.
**Option B:** **Lungs** – Pulmonary TB is rare in congenital cases due to the lack of aerosol exposure; instead, lymphatic seeding dominates.
**Option C:** **Brain** – CNS involvement (tuberculous meningitis) occurs in disseminated TB but is less common than lymph node involvement in congenital cases.
**Clinical Pearl / High-Y