The benign fibroosseous lesion: its association with paranasal sinus mucoceles and its MR appearance.

Although fibrous dysplasia and ossifying fibroma of the facial bones may, with some difficulty, be distinguishable pathologically, they are inseparable radiographically. Based on a study of 30 patients, there was no good or reliable imaging correlation with the histology and the degree of ossification or the bone(s) involved. Therefore, "benign fibroosseous lesion" has been proposed by several noted bone authorities as the term for these entities. Eleven patients had MRI and the overall signal intensities were low on both T1-weighted and T2-weighted sequences. Areas of high signal intensity on T2-weighted imaging correlated with either cysts within the lesion or the presence of mucocele, especially in the frontoethmoid region. Four such mucoceles are presented. The coexistence of mucoceles and benign fibroosseous lesions may be more common than previously reported. It is both realistic and appropriate for the radiologist to diagnose these entities as benign fibroosseous lesions and leave the final histologic diagnosis to the pathologist who can diagnose most such cases, albeit with some difficulty. Sites of high signal intensity on T2-weighted imaging in the frontoethmoid area should raise the possibility of a coexistent mucocele.