“…Thus, lines of directly adjacent stiff fibrotic tissue and pliable native lung parenchyma exist, along which considerable tension is likely to occur throughout the ventilatory cycle, leading to pleural tearing and pneumothorax. Although speculative, this appears to be corroborated by previous studies showing an increased risk of pneumothorax in idiopathic pulmonary fibrosis (in which discontinuous subpleural fibrosis is also common), 14 and higher risk of recurrent pneumothorax in pulmonary fibrosis. 15 Histomorphologically, the so-called 'apical cap', which is a localised lesion of subpleural fibrosis that predominantly occurs in the apices of the upper lobes, enters the differential diagnosis of pleuroparenchymal fibroelastosis.…”