Imaging update in spondyloarthropathy

Abstract

Although our understanding of axial spondyloarthropathy (axSpA) has increased recently, there has not been a concurrent improvement in patient diagnosis with delays contributing to patient morbidity. Imaging findings of axSpA can be subtle and may be dismissed often due to lack of understanding by reporters and importantly clinicians who do not suspect the disease. Recognition of the importance of imaging has led to the inclusion of MRI as part of the diagnostic criteria for axSpA. With this in mind, a number of advancements have been made in an attempt to increase our diagnostic accuracy on imaging. This article will give an overview of these techniques as well as a recap of the imaging features of axSpA.

Keywords: Inflammatory lesions; Rheumatology; Spondyloarthropathy; Structural lesions.

Fig. 1

Demonstration of the different entheseal fibrocartilage at the Achilles tendon. (a) T1-weighted sagittal image of the attachment of the Achilles tendon on the calcaneum. (b) Diagrammatic representation of different fibrocartilage at the insertion of the Achilles tendon. Entheseal fibrocartilage is not only noted at the tendon-bone junction but also at the sesamoid and periosteal fibrocartilage (which form the boundaries of the bursa). All these areas are prone to entheseal inflammation. (c) Coronal STIR MRI image of a female patient demonstrating thickening and high signal intensity oedema/inflammation of the right hamstring tendon at its insertion on the right ischial tuberosity (DASHED WHITE ARROW). Adjacent bone marrow oedema is also noted.

Fig. 2

a-d MRI STIR sequences demonstrating enthesitis at various sites. (a) Axial STIR MRI image demonstrating inflammation and oedema of the left iliopsoas muscle along with its myotendinous junction to its attachment on the left lesser trochanter. An iliopsoas bursa (WHITE ARROW) is noted with fluid deep to the iliacus muscle. Comparatively the right iliopsoas tendon is unremarkable. Note the very subtle bone marrow oedema (BMO) in the lesser trochanter enthesis with its surrounding increased adjacent soft tissue oedema. (b) Enthesitis of the right iliolumbar attachment with BMO and importantly soft tissue oedema (SOLID ARROW). (c) Axial oblique STIS sequences of the SIJ. At the inferior limits of the scan, florid enthesitis at the right gluteus medius attachment at the greater trochanter is noted. This highlights the importance of reviewing all sequences performed. (d) Sagittal MRI STIR sequences demonstrating calcaneal enthesitis at the plantar fascia attachment.

Fig. 3

Typical structural lesions seen in axial spondyloarthropathy. (a) Sagittal T1 image of the thoracolumbar spine demonstrating vertebral corner fat infiltration (SOLID ARROWS). (b) T1W coronal oblique image of the sacroiliac joint (SIJ). The solid arrows demonstrated typical tissue backfill representing fat metaplasia within an erosion. Notice the lesions are demarcated by the sclerotic border of the erosion and new cortical bone. Tissue backfill will be seen as high signal on STIR sequences (SOLID ARROWS in c). Note in (c) there are also subchondral inflammatory lesions bilaterally more so on the sacral side.

Fig. 4

Typical examples of structural lesions of spondyloarthropathy. (a) T1W sagittal lumbar spine image showing fatty infiltration and subsequent syndesmophyte formation (BLACK ARROW). Fatty corner lesions are noted at multiple levels. (b) Axial oblique T1W image of the sacroiliac joint (SIJ) and (c) T1W coronal image of the SIJs demonstrating ankylosis of the SIJs. (d) This lateral view of the cervical spine shows a rigid cervical spine in a patient with severe, long-standing ankylosing spondylitis. The spine is completely ankylosed (“bamboo spine”) due to syndesmophytes, fused facet (apophyseal) joints, and paraspinal ligamentous calcification.

Fig. 5

Summary of the ASAS classification and the varying definitions of classification criteria. Radiographic spondyloarthropathy (SpA) refers to patients in the clinical or imaging arm with evidence of sacroiliitis on X-rays of the Sacroiliac joint (SIJ), whereas non-radiographic SpA can be defined as inflammatory back pain in the absence of structural damage on conventional radiographs. The percentage of nr-SpA subjects is believed to be as high as 80% in the Imaging arm and 20% in the clinical arm. The progression of nr-SpA to the end stage of radiographic ankylosis is, as yet, undetermined.

Fig. 6

(a) T1W coronal oblique image of the sacroiliac joints in a 47year old male demonstrates low signal intensity focus on the left iliac subchondral aspect (SOLID ARROW). The corresponding STIR image (b) demonstrates diffuse high signal intensity in keeping with bone marrow oedema (BMO) and an inflammatory component (SOLID ARROW) in axial spondyloarthropathy. (c) T1 Volumetric interpolated breath-hold examination (VIBE) (d) Diffusion weighted image (DWI) and (e) apparent diffusion coefficient (ADC) map. The Left SIJ BMO on T1W and STIR is better appreciated as an erosion on the T1 VIBE (c). A focus of apparent restricted diffusion on trace (d), with ADC (e) high signal demonstrates T2 shine through phenomenon. Probably due to the fluid component in the erosion.

Fig. 7

MRI and Ultrasound (US) findings of Achilles enthesopathy in a patient confirmed to have axial spondyloarthritis. Longitudinal (a) and transverse (b) US section through the Achilles tendon demonstrating abnormal vascularisation of the cortical bone insertion on power Doppler imaging. The corresponding MRI (Sagittal T1 (c) and STIR (d) sequences) demonstrates fluid in the bursa (WHITE ARROW) and surrounding oedema and inflammation. Note the inflammation in the different fibrocartilage areas as previously discussed in Fig. 1.