Monostotic fibrous dysplasia of the cranial vault: a case report

Fibrous dysplasia, when it occurs in the craniofacial region, mostly involves the skull base and is rarely localized in the cranial vault. Although there have been several reports on magnetic resonance imaging (MRI) findings of fibrous dysplasia involving the skull base, cases occurring in the cranial vault have seldom been reported. We describe here a rare case of monostotic fibrous dysplasia that occurred in the parietal bone and discuss the characteristics of the MRI findings. A 47-year-old female was admitted to our hospital with a complaint of vertigo. A computed tomography (CT) scan did not reveal any intraparenchymal lesions in either the infra- or supratentorium, and her vertigo improved immediately without any treatments. However, a solitary osteolytic lesion was found incidentally in the left parietal bone. MRI showed that the lesion demonstrated hypointensity on T1-weighted images and hyperintensity on T2-weighted images, and was enhanced heterogeneously following injection of Gadolinium-DTPA. Removal of the parietal bone containing the lesion was performed according to the patient's wishes. The histopathological findings of the removed tissues corresponded to fibrous dysplasia. Although it is well known that craniofacial fibrous dysplasia demonstrates iso- or hypointensity on T1- as well as T2-weighted images, in the present case, the lesion showed apparent hyperintensity on T2-weighted images. These findings suggest that fibrous dysplasia can display various MR intensities depending on its origin.