Juvenile Aponeurotic Fibroma: An Ultrastructural Study

Abstract

The light and electron microscopic findings in a case of juvenile aponeurotic fibroma are described. The tumor was composed of fibromatosislike areas and cartilagelike islands with characteristic calcification. The ultrastructural study verified the cartilaginous nature of this tumor. The cartilagelike islands were made up of 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 a prominent Golgi complex. In the periphery of each cartilagelike island was a perichondriumlike structure exhibiting transitional features from fibroblastic cells to chondrocytic cells. The fibromatosislike areas consisted of spindle-shaped fibroblastic cells and occasional myofibroblasts. The morphologic pattern of the tumor somewhat mimics embryonal chondrogenesis, and the fibromatosislike areas may represent an overgrowth of the fibrous layer of the perichondrium. It is possible to regard this tumor as an organoid tumor having a capacity for bidirectional differentiation into cartilage and fibrous tissue.

FN1–EGF gene fusions are recurrent in calcifying aponeurotic fibroma

“…Given the presence of a signal peptide, it appears likely that the FN1–EGF protein enters the secretory pathway. This is supported by the granular and cytoplasmic EGF IHC staining pattern, consistent with location in the ER and Golgi complex, which is prominent in CAF .…”

“…In our CAF cases, RNA-seq showed high transcription of the entire FN1 gene consistent with a fibroblastic differentiation of the neoplastic cells [3,4,7]. There was selective transcription of the 3'-end of EGF, including the part encoding the mature EGF peptide, suggesting that the promoter of FN1 drives inappropriate expression of EGF.…”

“…Moderately cellular areas with bland, parallel‐arranged fibroblast‐like cells blend with less cellular, partly calcified fibrocartilage‐like nodules with small epithelioid fibroblasts and associated osteoclast‐type giant cells. Ultrastructurally, CAF shows evidence of both fibroblastic and cartilaginous differentiation .…”

Pediatric Fibroblastic and Myofibroblastic Lesions

“…27 Lesions that are histologically similar, with varying degrees of fibrosis are also described associated with drugs such as phenytoin and calcium channel blockers. 32 More rounded cells are often present adjacent to the calcification. The overlying epidermis may show hyperplasia.…”