Bronchial reserve cell hyperplasia

Bronchial reserve cells proliferate when the surface epithelium is shed during lung injury. In cytologic smears, hyperplastic reserve cells are observed as small, hyperchromatic cells, with smudged chromatin and scant cytoplasm; they are tightly packed and show nuclear molding.
They are distinguished from small cell carcinoma by their greater cohesiveness, their very small size and lack of mitoses and necrosis.