Mesectodermal leiomyosarcoma of the antrum and orbit.

A 39-year-old black man developed a left antral leiomyosarcoma that subsequently extended into the ipsilateral orbit. On light microscopic appearance of the antral tumor the presence of a distinctive myxoid and fibrillar cytoplasmic background suggested the diagnosis of a malignant Schwann's cell tumor. A second biopsy of the orbital extension displayed the same fibrillar character, but the emergence of tumor giant cells with cytoplasmic trichrome positivity also raised the possibility of a rhabdomyosarcoma. Electron microscopy demonstrated the smooth muscle derivation of the tumor, which probably originated from vascular smooth muscle elements. The atypical neural appearance of this myogenous tumor may have been caused by the extensive neural crest contribution to the cephalic connective tissues (mesectoderm). Radiation therapy and chemotherapy were ineffective.