The commonest intrabronchial cause of haemoptysis is
**Core Concept**
Haemoptysis refers to the coughing up of blood or blood-stained mucus from the respiratory tract. Intrabronchial causes of haemoptysis are related to conditions that affect the airways within the bronchi. The commonest intrabronchial cause of haemoptysis is often due to a specific condition that involves inflammation and erosion of blood vessels within the bronchial wall.
**Why the Correct Answer is Right**
The commonest intrabronchial cause of haemoptysis is bronchiectasis. Bronchiectasis is a condition characterized by irreversible dilatation of the bronchi, often due to chronic inflammation or infection. This leads to erosion of blood vessels within the bronchial wall, resulting in recurrent haemoptysis. The pathophysiology involves the destruction of the bronchial wall and the formation of bronchiectatic cavities, which can lead to the rupture of blood vessels and subsequent bleeding.
**Why Each Wrong Option is Incorrect**
**Option A:** Tuberculosis (TB) is a common cause of haemoptysis, but it is not the most common intrabronchial cause. TB typically causes extrabronchial haemoptysis due to the involvement of lymph nodes and interstitial tissues.
**Option B:** Lung cancer is a leading cause of haemoptysis, but it is not an intrabronchial cause. Lung cancer typically arises from the epithelial lining of the bronchi, but it is a neoplastic process rather than an inflammatory or infectious one.
**Option C:** Pulmonary embolism is a common cause of pulmonary infarction, but it is not typically associated with intrabronchial haemoptysis. Pulmonary embolism usually presents with acute respiratory distress, hypoxia, and possibly pleuritic chest pain.
**Clinical Pearl / High-Yield Fact**
Bronchiectasis is often associated with chronic respiratory infections, such as pulmonary tuberculosis, cystic fibrosis, or bronchitis. Repeated episodes of haemoptysis in a patient with chronic respiratory symptoms should raise suspicion for bronchiectasis.
**Correct Answer:** C.