Pseudoanaplastic giant cell tumor of bone

Marked nuclear atypia can be found in a variety of benign mesenchymal tumor s, including ancient schwannomas, symplastic leiomyomas, osteoblastomas, an d chondromyxoid fibromas. Such nuclear atypia is believed to represent a de generative phenomenon and does not indicate aggressive behavior. Separation of these pleomorphic but benign lesions from true sarcomas may be difficul t. We are aware of only one prior description of such degenerative atypia i n benign giant cell tumor of bone. We report a benign giant cell tumor of b one arising in the sacrum of a al-year-old white female. Preoperative embol ization of this lesion had been performed, and subsequent curetting reveale d marked atypia suggestive of an anaplastic malignancy. However, only very pare mitotic figures were present, and the radiographs were consistent with a benign giant cell tumor. A diagnosis of benign giant cell tumor was made , and no recurrence or metstases have been observed during the 4-year posto perative period.