Aggressive fibromatosis involving the paramandibular soft tissues. A study with the aid of electron microscopy

The distinction at the level of light microscopy between aggressive fibromatosis and low-grade malignancies with fibroblastic features may be difficult. An electron microscopic study of four cases of aggressive fibromatosis of the mandibular soft tissue was undertaken to determine whether any ultrastructural characteristics could be identified that would aid in a more uniform distinction between these lesions. The pertinent findings include the identification of cells of fibroblastic derivation showing a range of organelle-poor to organelle-rich features, cytoplasmic microfibrils, and dilated rough endoplasmic reticulum profiles. These features are discussed in the light of previously published findings of other forms of aggressive fibromatosis and closely related lesions. The study reaffirms that although electron microscopy may be useful in confirming the cell of origin in these lesions, the accurate diagnosis of fibrous tumors still rests with the proper correlation of clinical and light microscopic features. Clinical follow-up of the cases supports both the diagnosis of aggressive fibromatosis and the recommended treatment of adequate local excision.