Microscopic honeycombing
Microscopic honeycombing

Microscopic honeycombing is a very common finding in UIP. There is controversy over the origin of this lesion, but it is composed of normal-appearing bronchiolar epithelium (arrow) lining small cystic spaces that are typically filled with mucous (m) and acute inflammatory cells. One hypothesis holds that microscopic honeycombing is the result of complete alveolar loss in the lobule, with only the terminal bronchiole and pulmonary artery branch remaining.