[Imaging in patients with axial spondylarthritis with focus on new bone formation]

To summarize, the currently available imaging procedures have various possibilities to visualize or sometimes to predict the osteogenesis pathognomonic for axial spondylarthritis (axSpA). The individual imaging techniques of X‑rays, computed tomography (CT) and magnetic resonance imaging (MRI) all have strengths and weaknesses in the diagnostics of axSpA. The generally easily available X‑ray imaging rapidly provides information on the condition of large sections of the skeleton. In particular, it can depict the chronic stages with various structural alterations of the sacroiliac joint and syndesmophytes and ankylosis of the spine. The CT technique, which principally has the same contrast as X‑rays, also shows pathological ossifications but without superimpositions, with better resolution of details and a higher dimensionality. The MRI technique has a superior soft tissue contrast so that acute inflammatory stages, such as bone marrow edema and erosion of the edges of vertebrae of the spine (shiny corners, Romanus lesions) or erosions and bone marrow edema of the sacroiliac joint are easily visible. Bony reconstruction processes can be visualized better in X‑ray imaging and particularly in CT, which increases the evidential value of X‑ray, CT and MRI techniques. The positions of conventional radiography and MRI are well-established in the diagnostic algorithm; however, low-dose CT of the spine is still in the experimental stage but the initial results look promising.