Cytogenesis of Schwannoma (Neurilemoma), Neurofibroma, Dermatofibroma, and Dermatofibrosarcoma as Revealed by Electron Microscopy

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Abstract
Electron microscopic examination of schwannomas and neurofibromas revealed the Schwann cell identity of their predominant cells. Their structural differences appear to be related to quantitative variations in their collagen content. The ultrastructural features of schwannomas were similar despite their anatomic site of origin. Both neural neoplasms contained cross-banded fibers, most probably representing long-spacing collagen. The subcellular nature of these structures precludes their usefulness as a practical diagnostic aid. The ultrastructural characteristics of amputation neuromas mimic fascicles of normal nerve and may easily be distinguished from schwannomas and neurofibromas. Dermatofibromas, whose cellular population exhibits characteristics of fibroblasts and histiocytes, are also different from these neural neoplasms. No evidence was obtained to support the view that suggests a neural origin of dermatofibromas. Although their derivation from peri- or endo-neural fibroblasts cannot be unequivocally excluded, this possibility is minimized. The cells of a metastasizing dermatofibrosarcoma closely resembled those of the dermatofibromas, except for their larger nuclei and nucleoli and more abundant cytoplasmic organelles, features which appear to be compatible with their biologic behavior.