Answer: Paget’s disease

Histology: Paget’s disease, in its late stages, can almost always be diagnosed by its radiographic features. These show a diffused radiodensity which is formed by very distinct cortical thickening and trabecular coarsening. Histologically, the features of Paget’s disease center around the morphologic expression of chaotic bone remodeling. There is a mosaic pattern of cement lines and evidence of very active osteoclastic erosion and osteoblastic bone formation. The marrow space is filled with fibrotic, mildly inflamed tissue as a result of this exaggerated bone remodeling.

Discussion: Occasionally, Paget’s disease can be radiographically confused with a metastatic carcinoma. The carcinoma most likely confused with Paget’s is a prostate carcinoma which also produces radiodensity. However, the coarsening of the trabeculae is diagnostic of Paget’s disease. Histologically, the fibrotic, mildy inflamed tissue within the marrow space may be confused with the inflammation seen in chronic osteomyelitis. However, inflammation in bone does not indicate osteomyelitis unless there is an appropriate clinico-radiographic setting. Metastatic cancer may produce radiodensity and marrow fibrosis. Occasionally, keratin stains are necessary to rule out epithelial cells imbedded in the fibrous matrix.