Mesenchymal chondrosarcoma of the ethmoid sinus.

Mesenchymal chondrosarcoma arising from primitive mesenchymal cells is a distinctive type of chondrosarcoma that exists in both skeletal and extraskeletal forms. The tumor is composed of undifferentiated cells with focal areas of cartilaginous or chondroid matrix. An extremely rare case of mesenchymal chondrosarcoma of the anterior and middle ethmoid sinuses in a 16-year-old girl is presented. Magnetic resonance imaging provided more anatomic information about the tumor than computerized tomography and aided in surgical planning.