Figure 5  .

MRI and SJ biopsy specimen of a HLA B27+ 16 year old male juvenile AS patient with bilateral inflammatory low back pain and a disease duration of 7.5 years. (B). T2* weighted gradient echo sequence showing bilateral chronic changes with marked iliac subcondral sclerosis (s) and confluent erosions with consecutive pseudodistention of the joint spaces (white open arrows) in both SJ (bilateral chronicity grade III, bilateral activity grade b, not shown). (B) The biopsy specimen shows a subchondral cellular infiltrate partly invading the cartilage (black arrows). There are fibroblasts and activated lymphocytes in the infiltrate. In between are areas of bone formation (asterisks) and avital bone fragments (curved black arrow) and calcifications (haematoxylin and eosin staining, original magnification × 250).