Imaging of Paget disease of bone and its musculoskeletal complications: self-assessment module

Axial Spondyloarthritis: Mimics and Pitfalls of Imaging Assessment

Axial spondyloarthritis (axSpA) is a chronic inflammatory disorder that predominantly involves the axial skeleton. Imaging findings of axSpA can be divided into active changes, which include bone marrow edema, synovitis, enthesitis, capsulitis, and intra-articular effusion, and structural changes, which include erosions, sclerosis, bone fatty infiltration, fat deposition in an erosion cavity, and bone bridging or ankylosis. The ability to distinguish between imaging lesions suggestive of axSpA and artifacts or lesions suggestive of other disorders is critical for the accurate diagnosis of axSpA. Diagnosis may be challenging, particularly in early-stage disease and magnetic resonance imaging (MRI) plays a key role in the detection of subtle or inflammatory changes. MRI also allows the detection of structural changes in the subchondral bone marrow that are not visible on conventional radiography and is of prognostic and monitoring value. However, bone structural changes are more accurately depicted using computed tomography. Conventional radiography, on the other hand, has limitations, but it is easily accessible and may provide insight on gross changes as well as rule out other pathological features of the axial skeleton. This review outlines the imaging evaluation of axSpA with a focus on imaging mimics and potential pitfalls when assessing the axial skeleton.

MR Imaging Findings of Paget's Disease of the Spine

Paget's disease (PD) is a common bone disorder of the aging population where the spine is the second most common involved location after the pelvis. Though imaging findings are well described on CT and radiographs, recognition on MRI can be challenging. We reviewed 16 cases with radiologic or histologic confirmation of uncomplicated PD of the spine. In most cases, MRI showed a mixed pattern of increased/ decreased T1 signal (fine trabecular or coarse) of the vertebral bodies. There was also associated band-like decreased T1 and T2 signal of the endplates. This correlates with the mixed osteolytic and blastic phase of the disease, the most common phase in the spine. Subtle or conspicuous "picture-frame" appearance may also be identified. Present in most cases, but frequently overlooked manifestation on MRI, was the expansion of the vertebral body and/or posterior elements/ spinous process. We identified a subtle diffuse decreased T1 and T2 bone marrow signal, not corresponding to sclerosis on CT or radiographs, in two cases. We proposed this, as an earliest sign on MRI, likely representing early fibro-vascular bone marrow transformation and to our knowledge not previously described. Less commonly, sclerotic PD was also found which is perhaps the most difficult to evaluate given its broad differential. Most cases of PD of the spine were overlooked or confused with other entities by the radiologists. Interpretation of MR images of the spine in the absence of prior imaging is not uncommon. Thus, recognition of MRI manifestations is important to allow appropriate management, to avoid misinterpretations and in most cases to avoid biopsy.