T1-W mid coronal oblique image through the SIJ in a 42-year-old male who presented with long standing low back pain, raised inflammatory markers and a positive HLAB27. Juxta-articular geographical fat infiltration (blue arrows) is noted as structural lesions, along the sacral margin of the SIJ. Pseudowidening of the joint on MRI with large elongated erosions along the iliac aspect and subarticular sclerosis (curved arrowheads) of the right SIJ.