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MRI - technique
MRI-SIJ sequences/planes
MRI - sacroiliitis
Grading sacroiliitis
MRI-Spine sequences/planes
MRI - spinal changes
Grading spinal changes
Sacroiliitis changes by MRI

Early sacroiliitis changes present primarily as subchondral bone marrow edema (BME), which is a sign of active inflammatory changes. The changes can be symmetrical, asymmetrical and present on one or on both sides etc., as shown below.

With progressing disease, the changes are usually characterized by a mixture of signs of disease activity in the form of BME and structural joint changes in the form of erosions in addition to fat deposition corresponding to areas previously affected by active inflammation.

In more advanced disease stages, structural changes often dominate, but active changes may occur until the development of complete joint ankylosis.


Below are examples of changes that can generally vary considerably depending on activity and the development of structural change.

Early sacroiliitis changes
Very early sacroiliitis changes, coronal and axial STIR image in a patient with low back pain suggestive of sacroiliitis during 8 months. There is characteristic subchondral bone marrow edema (open arrows), most pronounced on the right side where there are changes on both sides of the joint.
Middle stage

Sacroiliitis changes in a patient with symptoms compatible with sacroiliitis for 3 years and a mixture of active and structural joint changes. The radiograph shows bilateral grade 3 changes. The concomitant MRI shows signs of disease activity in the form of bone marrow edema at the inferior part of both joints on the STIR image, most pronounced on the left side (open arrows). Erosions are seen on both sides on the T1-weighted and T1FS images (arrows) in addition to fat accumulation in the bone marrow, most pronounced in the sacrum on the right side (asterisks), changes compatible with ankylosing spondylitis.

Manifest sacroiliitis changes

Manifest sacroiliitis changes with predominantly structural changes in a patient with recognized ankylosing spondylitis for 5 years and a flare of symptoms with low back pain, especially on the right side. The radiograph shows bilateral grade 3 changes. The concomitant MRI shows signs of disease activity in the form of an area of edema in the bone marrow on the STIR image , including edema in an erosive area (open arrow), but the changes are predominantly characterized by structural changes in the form of erosions and fat deposition in the bone marrow (arrows), all features of ankylosing spondylitis.

Late stage with ankylosis

Semi-coronal T1-weighted, T1FS and STIR in addition to a semi-axial STIR image show obliteration of the SIJs with fat signal across the joint spaces, which are discernable on the T1-weighted sequence (ghost joints). There is no evidence of activity on the STIR image. Arthritis changes are partly visible on the axial STIR image and are seen clearly on the radiograph beneath.

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