Primary malignant ectomesenchymoma of the orbit.

Malignant ectomesenchymoma is a rare soft tissue tumor of the childhood believed to arise from a remnant of pluripotential migratory neural crest cell (ectomesenchym) and composed of both a mesenchymal element (most often embryonal rhabdomyosarcoma) and a neuroectodermal element (ganglioneuroma, schwanomma neuroblastoma or melanocytic cells). Reported sites of origin are the abdomen, perineum or scrotum, the extremities, the middle ear, nasopharynx, face, and neck. Herein we report a new case of an orbital ectomesenchymoma studied by means of histochemistry and immunohistochemistry in order to increase the morphologic and histogenetic knowledge of this peculiar tumor and its significance concerning the differential diagnosis.