Nodular fasciitis, a lesion of myofibroblasts. An ultrastructural study

Eight histologically typical cases of nodular fasciitis were studied by electron microscopy and histochemistry. The findings confirm accepted views of the morphology of this lesion, and also reveal the previously undescribed fact that nodular fasciitis is a lesion of myofibroblasts. Its cells have the basic ultrastructural features of fibroblasts. In addition, all cells contain peripheral, longitudinally oriented bundles of myofilaments and hemidesmosome‐like structures with associated basement membrane‐like material. Many cells have deeply clefted nuclei, desmosomes, and pinocytotic vesicles. These specialized features are identical to those of the myofibroblasts that have been described in granulation tissue, palmar fibromatosis, and other lesions. Thus far, myofibroblasts have been found in inflammatory and trauma‐related conditions and not in most studies of fibroblastic neoplasms. However, additional studies of proliferative and neoplastic fibroblastic lesions are needed to clarify the distribution and significance of myofibroblasts.