Vascular changes in cutaneous neurofibromas.

A variety of vascular changes has been associated with neurofibromatosis, and morphological alterations of arteries have been described previously. However, little attention has been paid to structural modifications of the microvasculature in neurofibromas themselves. Small vessels of 10 cutaneous neurofibromas, excised from patients with neurofibromatosis, were studied by using transmission electron microscopy and compared with normal skin vessels. The major alterations were: (1) increased thickness of the cytoplasm of endothelial cells which send numerous long processes to the lumen and, in some instances, obliterate it; (2) larger numbers of endothelial cell processes on the abluminal surface which are apposed to pericyte processes; (3) increased amounts of filaments and free ribosomes in the cytoplasm of endothelial cells, and (4) abundant pericytes with bundles of cytoplasmic filaments and many small subplasmalemmal densities. Mitotic figures were not seen in any of the vascular elements. These changes were interpreted to be the result of a generalized malformative process of blood vessels in neurofibromas rather than a consequence of the action of a tumor angiogenesis factor.