Ankylosing spondylitis, with bony ankylosis of the sacroiliac joints

In this 44-year-old patient, coronal images of the pelvis reveal fusion of the sacroiliac joints bilaterally. Sagittal images of the lumbar spine show vertebral body squaring and a bamboo like appearance due to diffuse ankylosis (and syndesmophytes). There is vertebral body fusion at multiple levels, with loss of disk space height and abnormal signal intensity within the disk spaces themselves. Note the “corner sign” present at multiple levels, a triangular sharply marginated corner signal abnormality (predominantly Modic type II) of the vertebral body, unassociated with an osteophyte or Schmorl node. This sign is important to recognize in routine clinical MR interpretation of the spine, as it suggests the diagnosis of ankylosing spondylitis.

Ankylosing spondylitis, ankylosis of sacroiliac joints
Part of the on-line supplement to Neuroradiology – The Essentials with MR and CT (© 2015)