Juvenile hyaline fibromatosis: ultrastructural study.

Juvenile hyaline fibromatosis is a multisystemic disorder characterized by a triad of cephalic fibrous outgrowths, gingival hyperplasia, and flexion contractures. The aim of this study was to find new ultrastructural features that could be useful for differentiating this entity from other types of fibromatosis. Mucosal lesions processed for light and electron microscopy by routine techniques showed hyperactive-appearing spindle-shaped fibroblasts and dysplastic mesenchymal cells. Dilated rough endoplasmic reticulum, prominent Golgi complexes, and multivesicular bodies as well as single membrane vesicles filled with fibrillogranular material were seen within the cytoplasm of dysplastic mesenchymal cells. Many fibrillogranular vesicles contained smaller vesicles. There were also invaginations of the cell membrane that contained fibrillogranular material similar to that seen in the single membrane vesicles, suggesting engulfment of an extracellular substance. The stroma contained both normal and serrated collagen fibrils, microfibrils, and two types of fibrillogranular material, one of them with a characteristic banding pattern. Our clinical and histopathologic findings resemble those previously described in cases of infantile systemic hyalinosis and juvenile hyaline fibromatosis. So many features of these two conditions overlap that it is difficult not to consider them as parts of a spectrum of the same disorder.