Ultrastructural study of cylindroma (Poncet-Spiegler tumor).

This report describes the ultrastructural characteristics of a Poncet-Spiegler tumor (cylindroma, turban tumor). This tumor was made up of two cell types and showed a ductal differentiation. Cells bordering duct-like structures were joined together by innumerable desmosomes, especially in places where the cell membranes were markedly invaginated. The arguments in favor of an eccrine or an apocrine for the origin of this sweat gland tumor are discussed.