Giant cell reparative granuloma of the ethmoid sinus.

This article represents the fourth and fifth reported cases of GCRG that involve the ethmoid sinus. The problems encountered in establishing the diagnosis are emphasized, as are the features that differentiate it from the giant cell tumor, aneurysmal bone cyst, and hyperparathyroidism, the conditions with which it is most commonly confused. The unusually aggressive behavior, as demonstrated by these two cases, is highlighted.