[Electron microscopic observation of acoustic neurinoma]

The ultrastructural pattern of the acoustic neurinoma was studied with 10 excised tumors as well as one from the temporal bone. Under transmission electron microscope, the ultrastructural characteristics of the tumor were as follows: (1) The cytoplasm formed bundles of very thin, long processes in intimate contact with each other and/or with similar processes from neighboring cells. (2) All of these cells and their processes were surrounded by a basement membrane. (3) In the dense areas, the extracellular spaces were occupied by banded fusiform fibers (Luse bodies). (4) In some tumors, the extracellular space of the loose areas contained a moderate amount of collagen. (5) The extracellular space in many tumors appeared either "empty" or filled with fine granular material and small bundles of fine filaments. Fully and partially myelinated nerve fibers were found in some tumors. Pathological classification based on the ultrastructure of the acoustic neurinoma had been discussed.