Fig. 11
Syndesmophytes and erosions in AS. (a) Lateral radiograph in a 29-year-old man with the characteristic slim ossification (syndesmophytes) at the periphery of the annulus fibrosus (black arrows) in addition to erosion of the endplates at the intervertebral (iv) space between L3 and L4 (white arrow). Supplementary MRI, (b) sagittal STIR and (c) T1-weighted images show small oedematous areas in the erosion at iv L3/4 on the STIR image and surrounding fatty marrow deposition on T1 as a sign of previous osseous inflammation. There are additional erosive changes (black arrows, c) not clearly delineated by radiography and slight oedema at the vertebral corners (white arrows, b). Note that the syndesmophytes demonstrated by radiography are not visible on MRI