Malignant oncocytoma of the maxillary sinus--an ultrastructural study.

A unique case of a malignant oncocytoma of the maxillary sinus is reviewed in detail. The ultrastructural findings are presented. The histologic and ultrastructural criteria that characterize oncocytes and the clinicopathologic features of benign and malignant oncocytomas are discussed. This case represents the eleventh reported case that would truly qualify as a malignant oncocytoma of the paranasal sinuses.