Juvenile Aponeurotic Fibroma: An Ultrastructural Study

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Abstract
The light microscopic and EM findings in a [human] case of juvenile aponeurotic fibroma are described. The tumor was composed of fibromatosislike areas and cartilagelike islands with characterisitc calcification. The ultrastructural study verified the cartilaginous nature of this tumor. The cartilage-like islands were made up to chondrocytic cells embedded in an abundant intercellular matrix containing fine fibrils, spherical granules and pleomorphic membrane-bound vesicles. The chondrocytic cells had many microvilli, a well-developed granular endoplasmic reticulum and prominent Golgi complex. In the periphery of each cartilage-like island was a perichondrium-like structure exhibiting transitional features from fibroblastic cells to chondrocytic cells. The fibromatosis-like areas consisted of spindle-shaped fibroblastic cells and occasional myofibroblasts. The morphologic pattern of the tumor somewhat mimics embryonal chondrogenesis, and the fibromatosis-like areas may represent an overgrowth of the fibrous layer on the perichondrium. It is possible to regard this tumor as an organoid tumor having capacity for bidirectional differentiation into cartilage and fibrous tissue.