Congenital fibromatosis (myofibromatosis) of the orbit: a rare cause of proptosis at birth.

A full-term infant boy had proptosis OS at birth: A large solid tumor mass was found by examination and computed tomographic scan in the orbit and extended intracranially. Biopsy showed spindle-shaped tumor cells that, with electron microscopy, proved to be myofibroblasts. Congenital fibromatosis (myofibromatosis) is a benign localized tumor of which this case is a striking example.