Subperiosteal ganglion associated with Paget's disease of bone.

Tumoral lesions related to Paget's disease may be classified as malignant, benign or pseudotumoral. While sarcomatous degeneration is the most feared complication, awareness of benign and pseudotumoral lesions is essential for assisting in accurate histological interpretation of the biopsy sample, which may avoid unnecessary repeat biopsies. We present the first case of a juxta-articular subperiosteal ganglion associated with Paget's disease, with classic imaging characteristics, especially on CT examination. The well-defined soft tissue mass at the medial aspect of the obturator rim, adjacent to a small fracture in pagetic quadrilateral plate, showed an ossified rim and internal gas lucencies, these being the hallmarks of a juxta-articular subperiosteal ganglion. On MRI, the lesion was of intermediate signal intensity on T1-weighted sequences, increased signal intensity on T2-weighted sequences, with rim enhancement after gadolinium contrast injection and preservation of fatty marrow signal of the underlying pagetic bone. Identification of the entity avoided an unnecessary biopsy or surgical intervention.