Fig. 5.

A 35-year-old man with psoriasis and psoriatic spondylarthropathy. MRI of the pelvis demonstrates a single inflammatory lesion in the left SIJ seen on two adjacent slices, this was best appreciated on the coronal STIR sequence (a, b, arrows). This patient therefore has sacroiliitis. Had the lesion been seen on only one slice, sacroiliitis could not be diagnosed using the ASAS criteria. Sacroiliitis is not visible on the normal-appearing radiograph of the SIJs (c). There is mild involvement of the spine. The sagittal STIR sequence demonstrates mild bone marrow oedema-like change on the anterior aspect of C2 (d, arrow) consistent with enthesitis. The arthropathy is better seen in some costovertebral joints (e, arrow), axial reformat of a sagittally acquired 3D sequence. Volume 3D sequences of the spine enable assessment of all costovertebral and costotransverse joints and can help make the diagnosis. The patient also complained of left foot pain, sagittal T2 fat sat MRI showed enthesitis at the origin of the abductor digiti minimi (f). Bone marrow lesions are not usually visible with ultrasound, CT or radiographs. Whole body bone scintigraphy demonstrated several areas of abnormal activity but the sacroiliitis and the spine involvement are not appreciable (g)