Tumorlets of the lung--an ultrastructural study.

A tumorlet of the lung is a minute tumorlike lesion found in damaged lungs in close association with the bronchioles. Histochemical and ultrastructural studies identify proliferating cells in the tumorlets as Kultschitzky-type cells. However, the pathological significance of the tumorlets, whether they are hyperplastic or neoplastic, is still controversial. Previous ultrastructural studies on the tumorlets have been carried out on formalin-fixed lung tissues. The case examined in this study was of typical tumorlets found in a so-called middle lobe syndrome of the lung of a 52-year-old woman. Tumorlets were located within the bronchiolar mucosa surrounded directly by a basal lamina and by the bronchiolar nonendocrine epithelial cells. There were no signs of invasion into the surrounding connective tissues or into lymphaticlike spaces. Between the covering bronchiolar epithelial cells and the subjacent proliferating Kultschitzky cells, specific sites of cell-to-cell attachment were noted. This finding, in addition to previously reported clinicopathological characteristics, indicates that the proliferating Kultschitzky-type cells in the tumorlets might be non-neoplastic and that tumorlets are due to hyperplasia of pure Kultschitzky-type cells, thus resembling neuroepithelial bodies of the lung.