Fibromatosis hyalinica multiplex juvenilis

Electron microscopic study of a case of fibromatosis hyalinica multiplex juvenilis (FHMJ) has revealed entangled tubular structures and an abundance of particles 40-60 nm in diameter in the cytoplasm, in addition to the previously described dilatation of the cisterna of endoplasmic reticulum--the "fibril-filled balls." The development of a tumor in FHMJ, therefore, involves abnormal propagation of cells, organelles, and their secretory products. The morphologic findings and the natural course of the disease suggest that this entity may be bordered between an abnormal proliferation and a true neoplasm of fibroblastlike cells.