Ultrastructure of osteoclastoma-like giant cell tumor of thyroid.

An aggressive anaplastic tumor of the thyroid with osteoclastoma-like giant cells was studied by electron microscopy. The lack of junctional complexes or other obvious epithelial elements suggested mesenchymal origin. The giant cells resembled osteoclasts with respect to mitochondria, rough endoplastic reticulum, lysosomes, ribosome complexes and vacuoles, but the prominent nuclear golgi apparatus of giant cell tumors of bone was absent.