Tension Pneumothorax

A 22-year-old tall, thin male smoker presents to the emergency department with sudden-onset severe right-sided pleuritic chest pain and rapidly progressive dyspnea. On examination, he is in severe respiratory distress (RR 38, HR 142, BP 76/40 mmHg), with tracheal deviation to the left, absent breath sounds over the entire right lung field, and markedly raised jugular venous pressure. A portable chest radiograph is obtained after needle thoracostomy and chest drain insertion. The structure marked **A** in the diagram—the complete right-sided pneumothorax with clearly visible visceral pleural line—is the radiological hallmark of which clinical entity?