Bilateral hand X-rays were performed in a 58-year-old man for suspicion of arthritis.
An incidental osseous lesion was found in the left wrist (Fig. 1). Radiographs showed an eccentric expansile epimetaphyseal bone lesion in the distal radius that abutted the articular surface. There was no evidence of cortical destruction. The lesion had a predominantly ground-glass appearance with some remnant trabeculae and internal foci of sclerosis. It had a well-defined wedge-shaped lytic leading margin without marginal sclerosis. Radiocarpal joint space was preserved.
MRI was performed (Fig. 2) showing a lesion with heterogeneous signal intensity: increased signal intensity on PD and T2W images and low signal intensity on T1W images with foci of intermixed yellow marrow.
The lesion was misdiagnosed as a giant cell tumour and the patient underwent surgery. Anatomopathological study demonstrated typical findings for Paget disease, which are shown on Figure 3. Multiple multinucleated osteoclastic giant cells and osteoblasts were seen, causing both osseous resorption and formation.
The disease was named after Sir James Paget, who first described it as “osteitis deformans” in 1877 . It is a common disease that usually occurs in people over 40 years of age .
Twenty percent of patients are asymptomatic at diagnosis .
Three sequential stages, that may coexist, have been described for Paget disease. Stage I is the osteolytic phase in which osteoclasts are activated causing bone resorption. Stage II is the mixed lytic and blastic (active) phase and corresponds to an osteoblastic activation with osseous formation in response to osteoclastic bone resorption. Stage III is the blastic phase in which osteoblastic activity decreases .
Anatomopathologically, this results in thickened and disorganized trabeculae, forming a mosaic pattern, with characteristic basophilic cement lines along the thickened trabeculae. The normal yellow marrow is replaced by fibrovascular tissue in the active phase .
The axial skeleton is the most commonly affected, the most frequent locations being the pelvis, spine and skull .
The osteolytic phase predominates in the long bones . The radiographic appearance is that of a bone lesion with a well-defined, wedge-shaped osteolytic leading margin, without marginal sclerosis, that represents the osteolytic phase. This leading margin is similar to a flame or a blade of grass, a feature that is unusual for a neoplasia. The osteolytic phase almost always begins in the subchondral bone of the epiphysis and advances (about 1 cm per year) into the metaphysis and diaphysis. Behind the lytic leading margin, mixed lytic and blastic phase disease develops with a disorganized pattern. Cortical bone thickening and trabecular bone thickening with bone expansion characteristically develop. In other cases, like ours, a hazy ground-glass or “washed-out” pattern might be seen with obliteration of bony trabeculae . Internal focal zones of sclerosis can be observed in the epiphysis or metaphysis while the lytic phase extends towards the diaphysis.
MRI appearance depends on the stage and consequent histological composition of the lesion . In the lytic to early active phase the lesion has heterogeneous signal intensity with typically intermixed foci of maintained yellow (fatty) marrow, that exclude malignant transformation.
As in our case, Paget disease might be discovered incidentally in asymptomatic patients. Therefore, it is important to be familiar with its typical radiographic appearance to avoid misdiagnosis. Radiologists should consider it in the differential diagnosis of epiphyseal or epimetaphyseal bone lesions with a well-defined osteolytic margin.
Differential Diagnosis List
Paget disease of the distal radius
Giant cell tumour
Plasmacytoma or multiple myeloma
Intraosseous ganglion cyst
Clear cell chondrosarcoma
Paget disease of the distal radius