Giant-cell tumor of bone arising from the falx cerebri. A case report

The histological and ultrastructural features of a giant-cell tumor of bone arising in the falx cerebri of a 27 year-old man are described. The tumor was embedded in the medial aspect of the left frontal lobe and was not attached to any of the bones of the skull. At surgery, the tumor was lightly adherent to the falx and was easily extracted. Histologically, the tumor was composed of mononuclear spindle-shaped and ovoid stromal cells, multinuclear giant cells containing 20-30 nuclei, and foci of osteoid and bone production. Hemorrhagic and cystic areas were also present within the tumor. Ultrastructurally, the spindle-shaped cells resembled fibroblasts and were surrounded by small bundles of collagen fibrils. The ovoid cells contained numerous mitochondria, abundant rough endoplasmic reticulum, vesicles, lysosomes, phagosomes and osseous material in the cytoplasm suggesting their monocyte-macrophage lineage. These cells were closely apposed and displayed evidence of fusion in the form of focal and linear subplasmalemmal densities to form multinucleated giant cells with similar organelles and multiple nuclei. It is suggested that the primary giant cell tumor of the one arose from the metaplastic ossification of the falx. To our knowledge, a giant-cell tumor of bone arising from the falx cerebri has not been previously described.