Fibrous dysplasia and cemento-ossifying fibroma. A histologic spectrum.

Fibrous dysplasia (FD) and cemento-ossifying fibroma (COF) are benign fibro-osseous lesions that are generally considered to be separate entities, distinguished by histologic and radiographic features. In our experience, some lesions lack the classic clinical, radiographic, or pathologic features of FD or COF and rather have overlapping features of both entities. Consequently, these cases are frequently diagnosed nonspecifically as fibro-osseous lesions. We examined 56 gnathic and extragnathic fibro-osseous lesions of bone morphologically, clinically, and radiographically to determine whether they can be reliably distinguished and whether their distinction has any clinical or prognostic significance. The lesions exhibited a broad morphologic spectrum of patterns ranging from pure FD (24 cases) to pure COF (10 cases). Twenty-two lesions contained a mixture of both patterns; 11 lesions with a predominant FD pattern contained calcified spherules histologically indistinguishable from those characteristically seen in COF. The remaining 11 lesions contained areas of typical FD adjacent to areas of COF. The lesions examined also demonstrated considerable radiographic overlap, and FD could not be reliably distinguished from COF. The recurrence rate was low for all lesions regardless of the histologic pattern. Because of histologic and radiographic overlap and similar low recurrence rate of FD and COF, we consider them to be related lesions, and COF is probably an opposing end of a morphologic spectrum of FD.