MRI is considered the most sensitive modality for detecting inflammatory changes in the initial diagnosis of seronegative arthropathy. At our institution we have incorporated imaging of the spine, thorax, pelvis and sacroiliac joints into an 'inflammatory spine' protocol, we utilise the protocol in practice to assess disease activity, monitor and evaluate therapeutic response. The sequences and MRI parameters utilised in our trust are as follows:

Active inflammatory lesions are best imaged on fluid sensitive sequences, with structural damage and chronic lesions being best visualised on T1 sequences. Typical findings in active disease include bone marrow oedema, synovitis and capsulitis, and ethesitis. Chronic changes include subchondral sclerosis, bony erosions, fat deposition and ankylosis [4].

MRI features of acute vs chronic disease

Active inflammatory changes in the sacroiliac joints

Fig. 1: MRI of the sacroiliac joints in a 41 year old male patient demonstrating active inflammation within the right sacroiliac joint. There is right sacroiliac bone marrow oedema evidenced by high peri-articular and subchondral signal intensity on the STIR sequence (a) with corresponding intermediate signal intensity on the T1-weighted sequence (b). There is also right sacroiliac joint effusion demonstrated by increased signal intensity within the joint space, best appreciated on the STIR sequence (a).

Fig. 2: MRI of the sacroiliac joints in a 56 year old female demonstrating bilateral active inflammation. Bilateral bone marrow oedema evidenced by high peri-articular and subchondral signal intensity on the STIR sequence (a) with corresponding intermediate signal intensity on the T1-weighted sequence (b). Bilateral sacroiliac joint effusions demonstrated by increased signal intensity within the joint space, best seen on the STIR sequence (a). There is also right sided capsulitis with bulging of the right sacroiliac joint, highlighted with arrow on STIR sequence (a).

Fig. 3: STIR MRI demonstrating left sided greater trochanter enthesitis in a 56 year old female patient (a) and 57 year old male patient (b). In both patients there is high signal intensity at the junctional area between the left greater trochanter and tendon of the gluteus medius, highlighted with arrows on the coronal slice (a) and axial slice (b).

Chronic inflammatory changes within the sacroiliac joints

Fig. 4: T1-weighted sequence showing ankylosis of both sacroiliac joints in a 70 year old male patient following chronic inflammation.

Fig. 5: MRI of sacroiliac joints in a 35 year old male patient showing chronic inflammatory changes associated with seronegative spondyloarthritis. There is subchondral sclerosis evidenced by low intensity at the joint surfaces on STIR (a) and T1-weighted (b) sequences, most notable at the left sacroiliac joint, highlighted by red arrow. There are also subtle joint erosions, best appreciated on the T1-weighted image (b), highlighted with the white arrow.

Active inflammatory changes within the spine

Fig. 6: MRI spine of a 41 year old male patient showing multilevel foci of high signal intensity at the posterior vertebral corners on STIR sequence (a), without corresponding signal change on T1-weighted sequence (a), highlighted by red arrows. These corner lesions are typical of active vertebral inflammation in spondyloarthritis and can occur at the posterior or anterior corners.

Fig. 7: MRI spine of a 44 year old male patient showing high signal intensity at the anterior vertebral corners of L2 and L3 vertebrae on STIR sequence (a), without corresponding signal change on T1-weighted sequence (b), highlighted by white arrows. Note also the absence of intervertebral disc degeneration, these corner lesions are suggestive of active inflammation within the vertebrae (osteitis) and enthesitis.

Fig. 8: Coronal STIR MRI of 41 year old male patient (a), 44 year old male patient (b) and 27 year old male patient (c) with active costovertebritis demonstrated by high signal at the costovertebral junctions, white arrows.

Chronic inflammatory changes in the spine

Fig. 9: Sagittal MRI spine of a 51 year old female patient demonstrating syndesmophyte formation and ankylosis of the cervical and thoracic spine, best appreciated on T1-weighted image (a). No features of accompanying acute inflammation demonstrated on STIR image (b).

Fig. 10: MRI spine of a 70 year old male patient with chronic seronegative arthropathy demonstrating ankylosis of the T7 – T9 vertebrae best appreciated on T1-weighted image (a). No acute inflammatory changes demonstrated on the STIR sequence (b).

Fig. 11: MRI spine of a 58 year female patient demonstrating fat deposition within the L5 anterior vertebral corner (arrow) on T1 weighted image (a), indicative of chronic inflammation at this site. These lesions are low signal on STIR sequence (b).

Incidental findings

Due to the extensive area covered in imaging, incidental findings (eg. pulmonary atelectais, diverticulosis, inguinal hernia, liver lesions, splenic lesions, pulmonary sequestration, nerve sheath tumours) are common in these studies, and require attention to detail in order to not be misinterpreted.

Fig. 13: MRI STIR thorax of a 37-year-old female with linear high signal parenchymal focus within the right upper lobe. This correlates with recent infective symptoms and pleurisy. Subsequent chest radiograph demonstrated resolution of the opacity which was presumed to reflect linear atelectasis.

Fig. 12: 45 year-old male with newly diagnosed psoriatic arthritis and history recurrent chest infections. Coronal STIR thorax (a) demonstrates fluid filled curvilinear mass within the right lower lobe, review of previous chest radiograph (b) demonstrated subtle left retro cardiac opacity. Subsequent Coronal CT thorax (c) confirmed the presence of intra-lobar pulmonary sequestration which was subsequently surgically resected.

Fig. 15: Patient with active axial seronegative arthritis (evidenced by thoracic vertebral endplate oedema and costovertebritis). Note also the presence of small cystic lesion within a normal size spleen, MRI appearances are most in keeping with a splenic cyst.

Fig. 14: Sagittal STIR MRI of the thoracic spine demonstrates a cystic posterior mediastinal lesion most in keeping with foregut duplication cyst.