The most likely cause of bihilar lymphadenopathy is –
**Core Concept**
Bihilar lymphadenopathy refers to the enlargement of lymph nodes in both hilar regions of the lungs, which can be a sign of various underlying conditions. This phenomenon is often associated with diseases that affect the lungs and the immune system.
**Why the Correct Answer is Right**
The most likely cause of bihilar lymphadenopathy is sarcoidosis, a systemic granulomatous disease characterized by the formation of non-caseating granulomas in affected organs. Sarcoidosis can cause lymph node enlargement in both hilar regions due to the accumulation of granulomatous tissue. The pathophysiology involves the activation of T lymphocytes and the formation of granulomas in response to an unknown antigen.
**Why Each Wrong Option is Incorrect**
* **Option A:** Tuberculosis (TB) is a possible cause of lymphadenopathy, but it typically affects one hilar region more than the other, known as unilateral hilar lymphadenopathy.
* **Option B:** Lymphoma can cause lymphadenopathy, but it is more commonly associated with unilateral or localized lymph node enlargement rather than bihilar lymphadenopathy.
* **Option D:** Pneumonia is an infection of the lung parenchyma and is not typically associated with lymphadenopathy.
**Clinical Pearl / High-Yield Fact**
Sarcoidosis is a classic cause of bihilar lymphadenopathy, and it is essential to consider this diagnosis in patients with respiratory symptoms and lymph node enlargement on chest imaging.
**Correct Answer:** C. Sarcoidosis.