Epithelioid granulomata in a nonossifying fibroma. The possible drug-induced mechanism

A 13-year-old boy affected by bursitis of the R knee and nonossifying fibroma of the distal metaphysis of the R femur, was treated in the weeks prior to surgical intervention with water-soluble aspirin tablets to relieve local pain. Unexpected epithelioid cell granulomata were observed inside the neoplastic fibrous stroma of the nonossifying fibroma. The coincidental appearance of a slight blood eosinophilia (7%) and perioral fixed drug eruption are clues that suggest that the histological bone findings may represent an expression of the hypersensitivity response elicited by aspirin. It cannot be ruled out that this unusual finding may be related to documented previous trauma, resulting in interstitial hemorrhages and subsequent reactive resorptive processes.