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?