Pulmonary tumorlet. A form of peripheral carcinoid

Twenty cases of pulmonary tumorlet are presented. Approximately one-third of the tumors occurred in lungs severely scarred by bronchiectasis or other inflammatory processes; the other two-thirds were found in lungs with little to no scarring. In the former instances, tumorlets were found in large scars in which identifying architectural features had been destroyed. In the latter, the tumorlets were seen in minute fibrous nodules, surrounding or obliterating small bronchi or bronchioles. Argyrophilic granules were demonstrated in 14 of 15 cases; in the electron microscope these were consistent with neurosecretory granules. Their location, silver staining properties, and ultrastructure suggest that pulmonary tumorlets are minute peripheral carcinoid tumors.