This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
45-year-old presents with persistent productive cough and clubbing. On auscultation, wheeze and crackles are present. Which is the most specific investigation to confirm the diagnosis? 
Select and explain. 
A. HRCT, B. Bronchoscopy with bronchoalveolar lavage, C. Chest X-ray, D. MRI
A: HRCT
Answer: A: HRCT 
Explanation: Ans. a. HRCTPersistence of a productive cough, clubbing, wheeze, and crackles is suggestive of bronchiectasis. HRCT is the diagnostic procedure of choice (most specific).HRCT findings in bronchiectasis:Airway dilation (detected as parallel "tram tracks" or as the "signet-ring sign").Lack of bronchial taperingBronchial wall thickening in dilated airwaysInspissated secretions (e.g., the "tree-in-bud" pattern)Cysts emanating from the bronchial wall (especially pronounced in cystic bronchiectasis)