Fine structure of epithelioid cells in cerebral tuberculoma

Abstract

The ultrastructure of epithelioid cells from a tuberculous granuloma in the cerebrum of a 26‐year‐old male was studied. Light microscopic examinations of the border zone of the brain tuberculoma constantly revealed epithelioid cells. Fine structural examinations demonstrated two main types (type 1 and type 2) of epithelioid cells. Both types of epithelioid cells contained similar large pale nuclei. The cell membrane had many finger‐like processes interdigitating with those of the adjacent cells. The type 1 cells were distinguished by the presence of abundant organellae such as lamellar rough endoplasmic reticulum and mitochondria making a dark tone of cytoplasm. The type 2 cells showed a pale cytoplasm containing a few Golgi complexes and associated variably shaped vesicles. Another finding of note in the type 2 cells was the presence of subplasmalemmal linear densities (SLD). The morphology of the type 1 epithelioid cells was reminiscent of that of plasma cells displaying a biosynthetic function. Type 2 epithelioid cells with SLD, however, appeared to have a reduced biosynthetic function and to have contributed to a persistence of the granuloma structure. Neither type revealed identifiable phagocytosed material, and evidence of pinocytosis was practically absent. The presence of morphologic features of transitional cells, intermediate between type 1 and type 2 cells, suggests that these cells are related. It appears likely that type 1 is an early form of type 2. This is supported by the fact that type 2 corresponded roughly to the type ‘B’, which is thought to be a terminal‐stage cell. Furthermore, dying cells exhibited the structure of type 2 rather than type 1 cells.