Fibrous cortical defect with bizarre nuclear features.

A femoral neck fibrous cortical defect with typical radiographic features had bizarre nuclear features on histological examination. Recognition of the benign radiographic appearance, similar bizarre features of accompanying macrophages, and paucity of mitoses led us to consider this a pseudoanaplastic ischemic or degenerative change in an old fibrous cortical defect. Because the biological behavior was not known with certainty, we closely followed this case. After 25 months, there has been no recurrence or regrowth. The close cooperation between the pathologist and other disciplines facilitates recognition of these pseudoanaplastic lesions and development of treatment strategies for lesions of unknown or uncertain biological behavior.