[Investigations on the ultrastructure of lympho-epithelial thymomas with special reference to "emperipolesis" (author's transl)].

The ultrastructure of eleven thymomas with lymphocytic predominance, one "epitheloid" cell thymoma and two normal human thymuses is described with special reference to "Emperipolesis". All patients have had myasthenia gravis. The normal human thymus consists of three parts: outer cortex, inner cortex, and medulla. The outer cortex contains mainly lymphoblasts and Metcalf's macrophages within the so-called "Clark-packet's". The inner cortex consists mainly lymphocytes and interdigitating reticulum cells, and the medulla of epithelial cells, lymphocytes and Hassall's corpuscles. In all cases of lympho-epithelial thymoma and in normal human thymuses there are enormous interdigitations between epithelial (tumor) cells, lymphocytes and macrophages. The "epitheloid" cell thymomas also show findings which suggest an epithelial cell interaction. We have not found intact lymphocytes inside the cytoplasm of normal and/or tumor epithelial cells, macrophages or interdigitating reticulum cells. The intracellular existence of intact lymphocytes has been termed "Emperipolesis" by Humble, Jayne, and Pulvertaft, meaning "internal wandering". These investigations indicate that "Emperipolesis" is not an adequate term for cellular interaction in normal human thymuses and thymomas. A false impression of intraepithelial location of thymic lymphocytes is created by two-dimensional sections of complex thymic structure. These ultrastructural studies revealed damage to lymphocytes only in macrophages with lymphocytolysis within these cells and accumulation of numerous heterophagic vacuoles containing fragments of lymphocytic debris within them.