<s>[INST] context: This patient's chest x-ray shows a pneumothorax, which is a collection of air in the pleural space. Patients with pneumothorax usually complain of sudden onset of dyspnea and unilateral pleuritic chest pain. Examination of the chest shows hyperresonance to percussion, decreased tactile fremitus, and decreased or absent breast sounds over the affected lung. Sometimes a pleural defect can act as a one-way valve and a tension pneumothorax can occur. This results in hypotension, tracheal deviation, and jugular venous distention, and requires urgent relief of the pneumothorax, usually with a chest tube. As in this patient, spontaneous pneumothorax may occur due to rupture of congenital subpleural apical blebs. This condition is usually seen in tall thin males under the age of 25. Pneumothorax may also be caused by trauma (especially with gunshot wounds and trauma causing rib fractures), following thoracentesis or with mechanical ventilation. Occasionally pneumothorax is seen in pneumonia (especially with Pneumocystis jiroveci and S aureus) and with lung cancer. All of these etiologies are unlikely in this patient who has been previously healthy. Pleural neoplasm usually causes a bloody pleural effusion, not pneumothorax. Patients who have pneumothorax often appear anxious, but anxiety is a result of the pain and dyspnea and is not the etiology. [/INST] question: A previously healthy 18-year-old high school student suddenly develops left-sided pleuritic chest pain and dyspnea while at the senior prom. In the emergency room examination reveals BP=110/60 mm Hg, P=110 beats/min, respiratory rate=36 breaths/min, T=37degC (98degF). There are hyperresonance to percussion, decreased tactile fremitus, and absent breath sounds over the left chest anteriorly. Chest x-ray is as shown.What is the most likely etiology of this patient's condition? | options: A: Infection of the lung parenchyma B: Malignant neoplasm of the pleura C: Rib fracture D: Rupture of a subpleural apical bleb | answer: D </s>