Figure 3.

 February 1998 (age 14 years and 8 months). (A) T₁ weighted fast spin echo image showing still normal width of the right sacroiliac joint. Band-like hypointensity in the iliac bone marrow, consistent with juxta-articular osteitis. The left anterior ilium shows a hypointense substrate (arrowhead), equivalent to an erosion and surrounding sclerosis. The posterior aspect shows an irregular hypointense configuration, indicating confluent erosions (double arrow) resulting in pseudodilatation of the joint. (B) Corresponding contrast enhanced T₁ weighted opposed phase gradient echo sequence reveals pronounced contrast enhancement, both on the right in the area of the juxta-articular osteitis (arrowheads) and on the left in the area of the erosions (double arrows) and posterior joint capsule. (C) Conventional radiograph shows slight subchondral sclerosis of the left iliac bone (black arrow) with two suspected iliac erosions (arrowheads).