Pulmonary Apical Cap-What's Old Is New Again

The pulmonary apical cap (PAC) is a morphologically distinct type of unilateral or bilateral fibroelastotic scar involving the lung apices. Despite being relatively common and having been described more than a hundred years ago, it remains underappreciated as a unique diagnostic entity by clinicians, radiologists, and pathologists alike. Given the centrality of modern chest imaging in the workup of diseases of the lungs, it may be expected that the PAC will be biopsied with increasing frequency. As such, pathologists should be familiar with its presentation, appearance, and differential diagnosis. This article serves as a short overview of PAC and as a practical aid in its diagnosis for surgical pathologists.