[Unusual, biphasic differentiated mesenchyma tumor of the frontal sinus. Benign fibromyxo-osteoma].

Myxomas, and especially fibromyxomas of the head and neck are rare but when occurring are usually located in the mandible. Here we present the case of a 24-year old man with an unusual mesenchymal tumor in the frontal sinus. Microscopic and histomorphological aspects demonstrated a benign tumor with biphasic differentiation (a myxoid and an osteoid part). The tumor was therefore classified as fibromyxo-osteoma. The association of two different tumors is not probable because of the extremely narrow topographic link between soft tissue and osteoid tumor parts. Other arguments against a perifocal myxoid reaction of the osteoma are that myxoid degeneration of osteomas is unknown and that appropriate immunohistochemical methods were able to show a relatively high proliferation activity of the spindle-shaped cells in the myxoid tissue. Therapy consisted of complete resection of the well-delimited tumor. The patient has remained free of any recurrence 2 years after primary therapy.