A19-year-old college sophomore comes to the emergency room because he has noticed a sudden onset of severe shortness of breath. it occurred while he was playing basketball. he is normally healthy and is a nonsmoker. he is an alert, thin, tall male in moderate discomfort secondary to respiratory distress. on physical examination of the lungs, the following is noted: hyperresonant to percussion over the left lung field; decreased to absent breath sounds on the left side and no adventitious sounds; decreased tactile fremitus on the left side. based on the history and physical examination findings, what is the most likely diagnosis?

Collapsed Lung (Pneumothorax)

Explanation:

"A pneumothorax is a collection of free air in the chest outside the lung that causes the lung to collapse.

[...]In some instances, the lung continues to leak air into the chest cavity and results in compression of the chest structures, including vessels that return blood to the heart. This is referred to as a tension pneumothorax and can be fatal if not treated immediately.

Examination of the chest with a stethoscope reveals decreased or absent breath sounds over the affected lung. The diagnosis is confirmed by chest X-ray."

Reference: George Schiffman. “Pneumothorax (Collapsed Lung): Symptoms, Causes & Treatment.” RxList, 2019