Alveolar soft part sarcoma: an electron microscopic study especially of uncrystallized granules using a tannic acid-containing fixative.

Electron microscopic observation of alveolar soft part sarcoma reveals crystalline structure as well as granules that are only partially composed of crystalloids. The uncrystallized part has been observed only as a dense amorphous substance by the conventional fixation method with glutaraldehyde or osmium tetroxide (or both). Some investigators have explained the uncrystallized areas as artifacts due to the fixation method and as being essentially crystallized; other investigators consider the dense amorphous material the prodromal state of crystallization. In this study, however, which used the fixation method most appropriate for the intracytoplasmic filaments (fixation in tannic acid-containing glutaraldehyde and postfixation in osmium tetroxide) after increasing the permeability of the filaments to the fixative by pretreatment with a nonionic detergent (Triton X-100), the uncrystallized part was revealed to consist of an aggregation of many uncrystallized filaments with the same diameter (6 nm) as that of the crystallized filamentous structures. That is, the uncrystallized part was found to have been present as the prodromal state of crystallization and as filaments.