Figure 1
a. The anatomy of the sacroiliac joint, with the synovial part (red) and the ligamentous part (blue). (Brown atlas of regional anesthesia: /das/book/0/view/1353/I4-u1.0-B1-4160-2239-2..50044-8--f3.fig/top) b. Oblique transaxial histological section obtained through the middle third of the SIJ, with the iliac bone and cartilage (I) to the left and the sacral bone and cartilage (S) to the right side. The ventral cartilaginous (VCJP) and dorsal ligamentous portion (DLP) of the joint is separated by the dorsal transition zone (TZ) containing the dorsal 2 mm of the cartilaginous joint facets and the ventral 2 mm of the ligamentous joint space. The ventral sacroiliac ligament (VSIL) is also shown. A marker of 10 mm shows the true size of the section [22].
Figure 2
a. Paracoronal slice direction along the long axis of the sacrum, perpendicular to the second sacral (S2) vertebral body; b. Axial slice direction.
Figure 3
Active and structural sacroiliitis in a 17-year-old girl with JSpA: no added value of Gd. a. Semicoronal STIR image shows high signal in the joint space at both sides and in the erosions (small arrows) and BME on the left sacral side (large arrow). b. Contrast-enhanced fat-saturated T1-weighted image shows synovial enhancement in both SI joints in the erosions (small arrows) and enhancing osteitis on the left (large arrow).
Figure 4
Active and structural sacroiliitis in a 16-year-old girl with JSpA: no added value of Gd. a. Semicoronal STIR image shows high signal in the joint space of both SI joints (small arrows) and bilateral BME (large arrows). Note also the bilateral extensive capsulitis (asterisk). b. Corresponding contrast-enhanced fat-saturated T1-weighted image shows synovial enhancement in both SI joints (short arrows), enhancing osteitis (arrows), and enhancing capsulitis on both sides (asterisk).
Figure 5
Active sacroiliitis with retroarticular enthesitis and capsulitis in a 14-year-old boy with JSpA: no added value of Gd. Axial and semicoronal STIR (a–b) and contrast-enhanced fat-saturated T1-weighted (c–d) images demonstrate enthesitis of the retroarticular interosseous ligaments and capsulitis on the right side (arrows).
Figure 6
Synovitis representing active sacroiliitis in a 14-year-old girl with JSpA. a. Semicoronal STIR image shows high signal in the joint space of the left SI joint, discrete also in the caudal part of the right SI joint, with b. synovial enhancement representing synovitis in both SI joints on the contrast-enhanced fat-saturated T1-weighted image. No BME is seen.
Figure 7
Flow chart for daily clinical practice for assessing sacroiliac joints on MRI in children (LBP = low back pain; MRI = magnetic resonance imaging; COR = coronal; STIR = short tau inversion recovery; AX = axial; BME = bone marrow edema; GD = gadolinium; CE= contrast-enhanced; FS = fat-saturated; FU = follow-up).
Figure 8
a. Paracoronal T1-weighted image of the sacroiliac joint, illustrating the ongoing ossification process, with open segmental and lateral apophyses of the sacral wing, resulting in a difficult delineation of the joint space due to the ongoing ossification process (small arrow). It is also very difficult to determine whether the nodular lesion in the right sacroiliac joint is an erosion (large arrow). b–c. Paracoronal T1-weighted images again illustrating the irregular outline of the developing sacroiliac joint, making assessment of erosions very hard. d. Paracoronal STIR image of the sacroiliac joint, illustrating the difficult assessment of bone marrow edema due to the high STIR signal of non-ossified cartilage in segmental (small arrows) and lateral (large arrows) apophyses.
Table 1
Typical Features of Sacroiliitis That Can Be Seen on MRI.
Active inflammatory lesions
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Structural/chronic lesions
|
[i] * Adapted from Sieper J, Rudwaleit M, Baraliakos X, et al., 2009 [15].
Figure 9
Active sacroiliitis in a 14-year-old boy with JSpA. a. Semicoronal STIR image shows a focal spot of BME at the iliac side of the right sacroiliac joint (arrow). b. Semicoronal contrast-enhanced fat-saturated T1-weighted image shows corresponding enhancement of this spot (arrow).
Figure 10
Ankylosis of the SI joint in an 18-year-old boy with JSpA. Semicoronal T1-weighted (a) and STIR (b) images show ankylosis of the right SI joint and narrowing of the left SI joint. No active lesions were seen.
Figure 11
Structural lesions of sacroiliitis in a 17-year-old girl with JSpA. Semicoronal T1 (a), STIR (b), and contrast-enhanced fat-saturated T1-weighted (c) images show irregular delineation of the right SI joint with subchondral sclerosis and fat. There are also subtle erosions and subchondral sclerosis on the left side. No enhancement is seen.
Figure 12
Multiple active and structural features of sacroiliitis seen on MRI in a 16-year-old girl with JSpA. a. Semicoronal T1-weighted image shows erosions and sclerosis in both sacroiliacal joints (arrows). b. Semicoronal STIR image shows high signal in the joint space of both sacroiliacal joints (short arrows) and bone marrow edema at the left iliac side (arrows). There is extensive capsulitis on both sides (asterisk). c. Corresponding contrast-enhanced fat-saturated T1-weighted image shows synovial enhancement in the erosions (short arrows) and enhancement at the site of the edema (arrows). Note also the enhancing capsulitis on both sides (asterisk).
Figure 13
Active and structural sacroiliitis in a 17-year-old boy with JSpA. a. Semicoronal T1-weighted image show extensive erosions of the SI joints (arrows). b. Semicoronal STIR image shows high signal in the joint space and within the erosions (arrows). No surrounding bone marrow edema is visible. c. Contrast-enhanced fat-saturated T1-weighted image shows synovial enhancement in the erosions and the joint space. Note also the enlarged lymph nodes along the iliac vessels (asterisk).
Figure 14
Active and structural sacroiliitis in a 15-year-old boy with JSpA. a. Semicoronal T1-weighted image shows erosions on both SI joints and subchondral sclerosis at the iliac side of the right SI joint (arrows). b. Semicoronal STIR image shows high signal in the joint space of both SI joints (short arrows) and bone marrow edema at the left iliac side (arrow). c. Contrast-enhanced fat-saturated T1-weighted image shows synovial enhancement in the erosions (short arrows) and enhancing osteitis (arrows).
Figure 15
Active and structural sacroiliitis in a 14-year-old boy with JSpA. Semicoronal STIR image shows erosions of both the SI joints with surrounding bone marrow edema and correct signal in the joint space (arrows).
Table 2
Types of findings required for definition of sacroiliitis by MRI
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Amount of signal required
|
Figure 16
Active sacroiliitis in a 17-year-old girl with JSpA according to global assessment as well as to the ASAS definition of a positive MRI for sacroiliitis. a. Semicoronal STIR image shows an active lesion with BME at the iliac side of the right sacroiliac joint on two consecutive slides (only one slide shown) (arrow). b. Corresponding semicoronal fat-saturated T1-weighted image shows vivid enhancement of this site (arrow).
Figure 17
Active sacroiliitis in a 15-year-old boy with JSpA according to a global assessment of MRI for sacroiliitis, not according to the ASAS definition of a positive MRI for sacroiliitis. a. Semicoronal STIR image shows a focal nodular high signal in the right sacroiliac joint representing an active erosion (arrow). b. Semicoronal contrast-enhanced fat-saturated T1-weighted image shows corresponding enhancement of this lesion (arrow).
Table 3
Proposal for a Pediatric-specific Definition of Sacroiliitis on MRI.
Types of findings required for definition of sacroiliitis by MRI
|
Amount of signal required
|
[i] Note: The differences between the adult (Table 2) and the proposed pediatric-specific definition of sacroiliitis are marked in italics.
Figure 18
Active sacroiliitis with synovitis/retroarticular enthesitis in a 14-year-old boy with JSpA according to a global assessment of MRI for sacroiliitis, not according to the ASAS definition of a positive MRI for sacroiliitis. a. Semicoronal STIR MR image demonstrates synovitis/retroarticular enthesitis of the right sacroiliac joint (arrows). b. Semicoronal contrast-enhanced fat-saturated T1-weighted image shows synovial enhancement and enhancement of the retroarticular interosseous ligaments (arrows).
Figure 19
Hip arthritis in a 14-year-old boy with JSpA. a. Axial STIR image shows a joint effusion in the left hip joint (arrow). Note also the small amount of fluid in the right hip joint. b. Axial contrast-enhanced fat-saturated T1-weighted image shows synovial enhancement at the left hip joint (arrow). No enhancement is seen at the right hip joint.
Figure 20
Axial STIR MR image in an 8-year-old girl with enthesitis-related arthritis shows enthesitis of the left gluteus maximus insertion (arrow).
Figure 21
a. Paracoronal STIR images in a 16-year-old girl with enthesitis-related arthritis demonstrates a left-sided enthesitis of the retroarticular interosseous ligaments as only finding at the first MRI of the sacroiliac joints. b. T1 image demonstrates that the high signal is seen in the retroarticular fat tissue and not in the cartilaginous part of the SI joint. c. Paracoronal STIR image at first MRI, two and three years later. Follow-up MRI in this patient shows formation of a small erosion at the iliac side of the left sacroiliac joint, evolving to a large erosion three years later.
Figure 22
Semicoronal STIR MR image of the SI joint in a 15-year-old boy with arthralgias (ERA-negative) shows edema at the origin of the gluteus medius muscle at the iliac crest representing enthesitis.
Figure 23
Axial STIR image in a 14-year-old boy with enthesitis-related arthritis shows high signal intensity in the left obturator externus muscle (arrow), representing hip enthesitis. Note also some fluid in the left hip joint (short arrows).
Figure 24
Axial STIR image in a 15-year-old boy with enthesitis-related arthritis demonstrates enthesitis of the left gluteus maximus insertion (arrow).
Figure 25
a. Semicoronal and b. axial STIR MR image in a 12-year-old boy with enthesitis-related arthritis demonstrates enthesitis of the retroarticular interosseous ligaments on the right side (arrows). Note also the sacroiliitis with fluid and capsulitis at the right SI joint (short arrows).