Pulmonary apical cap: a distinctive but poorly recognized lesion in pulmonary surgical pathology.

Thirteen cases of pulmonary apical cap (PAC), resected for the exclusion of a clinical diagnosis of lung carcinoma, were reviewed, and their distinctive morphology was described. PAC occurred in older individuals, particularly in the apices of the upper lobes, and by radiographic examination appeared as spiculated subpleural masses ranging from 0.7 to 5.2 cm in diameter. Microscopically, these subpleural scars were pyramid shaped with overlying pleural adhesions and hyaline pleural plaques. They were characterized by a dense basophilic fibrosis of the pulmonary parenchyma with air spaces filled with old, mature collagen and the underlying elastic skeleton contracted in an accordion-like fashion with reduplicated curls of elastic fibers. Scar emphysema was prominent at the periphery of these fibrous nodules. PAC should be recognized for its unique histology because its appearance in the surgical pathology laboratory will likely increase in incidence with the evolution of more sensitive pulmonary radiographic studies. A chronic ischemic etiology is favored.