DOI:10.2214/AJR.07.3446
AJR 2008; 191:1016-1023
© American Roentgen Ray Society
CT and MRI of Spine and Sacroiliac Involvement in Spondyloarthropathy
Alexis Lacout1,
Benoît Rousselin and
Jean-Pierre Pelage
1 All authors: Service de Radiologie, Hôpital Ambroise Paré, 9 Ave.
Charles de Gaulle, 92104 Boulogne, France.
Received November 20, 2007;
accepted after revision April 29, 2008.
Address correspondence to A. Lacout.
Abstract
OBJECTIVE. Spondyloarthropathies are rheumatoid diseases that
predominantly affect the axial skeleton, causing pain, stiffness, and
ankylosis. The aims of this article are to illustrate the different stages of
the diseases from early inflammatory involvement to ankylosis using CT and MRI
and to discuss the role of imaging in the management of affected patients.
CONCLUSION. CT and MRI are the most sensitive techniques in the
detection of axial involvement, permitting earlier diagnosis and optimized
treatment.
Keywords: ankylosing spondylitis • CT • MRI • sacroiliac joint • spondyloarthropathy
Introduction
Spondyloarthropathy is a general term for a group of chronic inflammatory
rheumatic diseases that predominantly affect the axial skeleton, causing pain
and stiffness [1]. Five
subgroups can be distinguished, including ankylosing spondylitis, reactive
arthritis (Reiter's syndrome), psoriatic arthritis, arthritis associated with
chronic inflammatory bowel disease, and undifferentiated spondyloarthropathies
[2]. These afflictions have in
common that they are seronegative for rheumatoid factor and often are
associated with the presence of HLA-B27
[3,
4]. Schematically, unlike
rheumatoid arthritis, which affects the synovial membrane,
spondyloarthropathies principally involve the enthesis
[5].
Although radiographs have been widely used in the past, CT and MRI are more
sensitive and specific for assessing involvement of the spine and sacroiliac
joint [2,
4–7].
Furthermore, CT and MRI may help in identifying the different stages of
enthesitis and therefore help in optimizing the man agement of patients
[2]. These different stages
include inflammatory involvement with bone erosions, fatty postinflammatory
degeneration, sclerotic changes, and bone formations in succession
(Fig. 1).
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Fig. 1 —Diagram shows different stages of rachidian involvement in
spondyloarthropathies. Early inflammatory changes are best shown on MRI (bone
marrow edema), although more chronic changes are best depicted on CT (bone
erosions, sclerotic changes, syndesmophytes). Pattern of sacroiliac joint
involvement is similar.
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Imaging
Rachidian Involvement
Rachidian involvement consists of inflammatory changes of the insertions of
the vertebral ligaments (enthesitis)
[5]. Histopathologic
examinations of enthesitis can reveal erosive lesions with infiltrating
macrophages and lymphocytes [8,
9]. The marrow spaces in the
immediate vicinity of the enthesis may show edema, lack of hemopoietic tissue,
and plasma cell infiltration
[8]. With imaging, the
successive stages of the disease from early inflammatory involvement to fatty
post inflammatory changes, bone formations, and ankylosis can be identified
[2]. These different stages may
be present in the same patient
[4].
The earliest inflammatory changes are best observed with MRI and consist of
the inflammatory appearance of the ligaments and of their insertions
(enthesitis) [2,
10]. However, CT appears to be
more sensitive for depicting chronic changes such as erosions, sclerotic
changes, and bone formations located at the same sites
[4]. Depending on the specific
site of the inflammatory involvement, four different entities can be
distinguished: spondylitis (Romanus spondylitis), spondylodiskitis (Andersson
aseptic spondylodiskitis), arthritis of the zygapophyseal joints, and true
ligamentous inflammatory involvement
[2,
8,
10].
Romanus spondylitis consists of inflammatory changes involving the edges of
the vertebral endplates. Involvement of the anterior edges is secondary to
enthesitis of the anterior longitudinal ligament, whereas involvement of the
posterior edges is secondary to enthesitis of the posterior longitudinal
ligament. MRI can show hyperintense edematous corners on T2- and T1-weighted
sequences with IV administration of gadolinium
(Fig. 1). Inflammatory bone
erosions of the edges of the vertebral endplates may be observed later on CT
[2,
10] (Figs.
2 and
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H).
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Fig. 2 —31-year-old woman with ankylosing spondylitis: Romanus
anterior and posterior spondylitis of thoracic spine. Gadolinium-enhanced
sagittal fat-saturated fast spin-echo T1-weighted image shows hyperintense
changes at anterior and posterior edges of vertebral endplates
(arrows).
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Fig. 3A —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement. Sagittal fast
spin-echo T1-weighted image shows circumscribed hypointensity of anterior
edges of vertebral endplates secondary to both edema and sclerotic changes
(arrows).
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Fig. 3B —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement. Sagittal
STIR-weighted image shows florid hyperintense Romanus lesions
(arrows).
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Fig. 3C —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement.
Gadolinium-enhanced sagittal fat-saturated fast spin-echo T1-weighted image
confirms vertebral inflammatory changes (arrows) and shows discrete
enhancement of interspinal and supraspinal ligaments
(arrowheads).
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Fig. 3D —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement. CT scan (sagittal
reformation) shows sclerotic changes and erosions of vertebral endplates
(arrows).
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Fig. 3E —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement. Sagittal
STIR-weighted sequence shows hyperintensity of vertebral endplates adjacent to
intervertebral disk, corresponding to Andersson aseptic spondylodiskitis
(arrows). Hyperintensity of bone marrow around zygapophyseal joints
corresponds to arthritis (arrowheads).
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Fig. 3F —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement. Coronal CT scan of
sacroiliac joints shows multiple subchondral erosions (arrows) and
sclerosis (arrowheads).
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Fig. 3G —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement. Frontal (G)
and lateral (H) radiographs of lumbar spine show discrete erosions and
densities of anterior vertebral endplates (arrows, G) and
presence of lateral syndesmophytes (arrowheads, H).
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Fig. 3H —29-year-old man with ankylosing spondylitis: Romanus anterior
spondylitis, Andersson spondylodiskitis, zygapophyseal joint arthritis, true
ligamentous inflammation, and sacroiliac joint involvement. Frontal (G)
and lateral (H) radiographs of lumbar spine show discrete erosions and
densities of anterior vertebral endplates (arrows, G) and
presence of lateral syndesmophytes (arrowheads, H).
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Andersson aseptic spondylodiskitis consists of inflammatory changes
involving the diskus and adjacent vertebral endplates, which appear
hyperintense on T2- and T1-weighted sequences after gadolinium administration
(Fig. 3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H). As observed in Romanus
lesions, bone erosions of the vertebral endplates may be observed later on CT
[2,
10].
Arthritis of the posterior joint may occur, with bone marrow edema,
effusion, and erosions and may undergo ankylosis at the end stage. MRI best
depicts early inflammatory changes
[2,
10] (Fig.
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H). The costovertebral and
costotransverse joints may also be involved
[2].
Although ligamentous lesions are most commonly confined to the bone
insertions, they can also involve other parts of the ligament, corresponding
to true ligamentous inflammation
[8]. True ligamentous
inflammatory involvement may be observed in the course of the disease using
MRI [2,
10]. Fat-saturated T1-weighted
sequences with administration of gadolinium are more sensitive than
T2-weighted or STIR sequences in the detection of this type of involvement.
All the vertebral ligaments may be affected, most often the interspinal and
the supraspinal ligaments (Figs.
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H and
4A,
4B,
4C,
4D). Inflammation of the bone
marrow adjacent to their insertions may be also seen
[2,
10].
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Fig. 4A —55-year-old woman with spondyloarthropathy (precise diagnosis
not yet established) and ligamentous inflammation. Gadolinium-enhanced
sagittal (A), coronal (B), and axial (C) fat-saturated
fast spin-echo T1-weighted images of L3–L4 level of lumbar spine show
strong enhancement of yellow ligaments (thin arrows) and of
interspinal and supraspinal ligaments (thick arrows, B and
C), corresponding to inflammatory involvement.
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Fig. 4B —55-year-old woman with spondyloarthropathy (precise diagnosis
not yet established) and ligamentous inflammation. Gadolinium-enhanced
sagittal (A), coronal (B), and axial (C) fat-saturated
fast spin-echo T1-weighted images of L3–L4 level of lumbar spine show
strong enhancement of yellow ligaments (thin arrows) and of
interspinal and supraspinal ligaments (thick arrows, B and
C), corresponding to inflammatory involvement.
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Fig. 4C —55-year-old woman with spondyloarthropathy (precise diagnosis
not yet established) and ligamentous inflammation. Gadolinium-enhanced
sagittal (A), coronal (B), and axial (C) fat-saturated
fast spin-echo T1-weighted images of L3–L4 level of lumbar spine show
strong enhancement of yellow ligaments (thin arrows) and of
interspinal and supraspinal ligaments (thick arrows, B and
C), corresponding to inflammatory involvement.
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Fig. 4D —55-year-old woman with spondyloarthropathy (precise diagnosis
not yet established) and ligamentous inflammation. Sagittal fat-saturated fast
spin-echo T2-weighted image shows discrete hyperintensity of interspinal and
supraspinal ligaments (arrows), less visible than with
gadolinium-enhanced fat-saturated fast spin-echo T1-weighted sequences.
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Later in the course of the disease, inflammation may decrease and
inflammatory zones may be replaced by fatty postinflammatory bone marrow
[2]. MRI may show fatty
infiltration at either edge of the vertebral endplates representing
postinflammatory changes after Romanus spondylitis or Andersson
spondylodiskitis [2]
(Fig. 5).
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Fig. 5 —45-year-old man with ankylosing spondylitis: postinflammatory
fatty vertebral changes after Romanus spondylitis. Sagittal fast spin-echo
T1-weighted image of thoracic spine shows circumscribed hyperintensity of
anterior edges of vertebral endplates corresponding to fatty infiltration of
bone marrow long after florid inflammatory Romanus spondylitis
(arrows).
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The last stage of spinal involvement consists of sclerotic changes, bone
formations, and ankylosis (Fig.
6). CT may be the best imaging tool for diagnosis, although MRI
may also detect such changes
[4]. However, in these cases,
radiographs may often be sufficient
[4]. Syndesmophytes, consisting
of bone outgrowth forming an osseous bridge between two adjacent vertebrae,
are characteristic of spondyloarthropathies
[4] (Fig.
7A,
7B). These bone formations are
different from osteophytes because their initial directions are not horizontal
but vertical. Syndesmophytes (end stage of Romanus spondylitis) are
responsible for the development of peripheral spinal ankylosis. Ankylosis may
also be central, secondary to bone formations passing through the disk (end
stage of Andersson spondylodiskitis). Ankylosis of the zygapophyseal joints
may also be observed [2]
(Fig. 6).
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Fig. 6 —73-year-old woman with ankylosing spondylitis:
postinflammatory vertebral sclerotic changes after Romanus spondylitis;
ankylosis of zygapophyseal joints. Sagittal vertebral CT scan shows sclerotic
change of anterior edge of vertebral endplates corresponding to
postinflammatory Romanus involvement (arrows). Bone constructions and
ankylosis of zygapophyseal joints (arrowhead) are also seen.
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Fig. 7A —80-year-old woman with ankylosing spondylitis:
syndesmophytes. Sagittal (A) and coronal (B) CT scans of
thoracic and lumbar spine show syndesmophytes corresponding to osseous bridge
between two adjacent vertebrae (arrows).
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Fig. 7B —80-year-old woman with ankylosing spondylitis:
syndesmophytes. Sagittal (A) and coronal (B) CT scans of
thoracic and lumbar spine show syndesmophytes corresponding to osseous bridge
between two adjacent vertebrae (arrows).
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Insufficiency vertebral fractures may occur in spondyloarthropathies and
are known as Andersson fractures. These fractures may be characterized by
ankylosis and osteoporotic changes
[2,
4,
11].
Sacroiliac Joint Involvement
Because the sacroiliac joints are predominantly made of fibrous connective
tissues (fibrocartilage) and contain very little synovial fluid, these
articulations may be considered entheses
[5,
12]. These features may
explain why sacroiliac joints are spared during rheumatoid arthritis and also
explain their characteristic involvement during spondyloarthropathies.
Sacroiliitis may be unilateral or bilateral. The different stages of
sacroiliac involvement on CT and MRI are similar to those observed in the
spine [2,
13]. The early inflammatory
changes of the joint are best detected with MRI, although erosions, sclerotic
changes, and ankylosis are also well depicted using CT
[4,
6,
7,
13].
The earliest signs of sacroiliitis are identified using MRI. Subchondral
bone edema is associated with increased signal in fat-saturated fast spin-echo
T2-weighted or STIR sequences and with contrast-enhancement in fat-saturated
fast spin-echo T1-weighted sequences after administration of gadolinium
[6,
7,
13] (Figs.
8 and
9A,
9B). Inflammatory enhancement
of the fibrous connective tissue of the joint may also be present
[6,
7,
13] (Fig.
10A,
10B). CT may initially depict
subchondral demineralization followed by bone erosions
[14] (Fig.
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H). Early diagnosis of either
sacroiliac or spinal inflammatory involvement helps in initiating early
treatment such as physiotherapy, nonsteroidal antiinflammatory drugs, or,
anti-TNF (tumor necrosis factor) agents, which, for example, may prevent the
end stage of ankylosis [4].
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Fig. 8 —21-year-old woman with spondyloarthropathy associated with
Crohn's disease: unilateral sacroiliitis. Coronal STIR-weighted sequence of
sacroiliac joints shows hyperintensity of right iliac subchondral bone marrow
(arrowhead).
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Fig. 9A —54-year-old man with ankylosing spondylitis: bilateral
sacroiliitis. Coronal STIR (A) and gadolinium-enhanced fat-saturated
T1-weighted (B) images of sacroiliac joints show hyperintensity of
subchondral bone marrow (arrows).
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Fig. 9B —54-year-old man with ankylosing spondylitis: bilateral
sacroiliitis. Coronal STIR (A) and gadolinium-enhanced fat-saturated
T1-weighted (B) images of sacroiliac joints show hyperintensity of
subchondral bone marrow (arrows).
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Fig. 10A —18-year-old man with ankylosing spondylitis: bilateral
sacroiliitis. Gadolinium-enhanced coronal fat-saturated fast spin-echo
T1-weighted image of sacroiliac joints shows enhancement of connective fibrous
tissues (arrows). Hyperintensity of right iliac subchondral bone
marrow (arrowhead) is also seen.
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Later in the course of the disease, inflammation usually decreases and
subchondral edema is progressively replaced by fatty postinflammatory bone
marrow, which appears hyperintense on T1-weighted sequences
[13] (Fig.
11A,
11B).
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Fig. 11A —25-year-old man with ankylosing spondylitis: postinflammatory
fatty infiltration after acute sacroiliitis. Coronal T1-weighted (A)
and STIR-weighted (B) sequences show T1 hyperintensity and STIR
hypointensity of subchondral bone marrow of right joint, finding indicative of
fatty infiltration (arrows). STIR-weighted image shows no
hyperintensity that would indicate active inflammatory involvement.
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Fig. 11B —25-year-old man with ankylosing spondylitis: postinflammatory
fatty infiltration after acute sacroiliitis. Coronal T1-weighted (A)
and STIR-weighted (B) sequences show T1 hyperintensity and STIR
hypointensity of subchondral bone marrow of right joint, finding indicative of
fatty infiltration (arrows). STIR-weighted image shows no
hyperintensity that would indicate active inflammatory involvement.
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The final stage of sacroiliac involvement consists of subchondral sclerosis
followed by fusion of the joint with ankylosis. At this stage, MRI may show
sclerotic changes, hypointense on T1- and T2-weighted sequences, and fusion of
the articulation [13] (Fig.
12A,
12B). However, in cases in
which radiographs and MRI are equivocal, CT may be the best imaging technique
for depicting subchondral density and sacroiliac ankylosis
[4] (Figs.
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H,
13, and
14A,
14B).
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Fig. 12A —35-year-old woman with ankylosing spondylitis:
postinflammatory sacroiliac sclerotic changes after acute sacroiliitis. Axial
(A) and gadolinium-enhanced fat-saturated (B) T1-weighted images
of sacroiliac joints show subchondral hypointensity indicative of sclerotic
changes (arrows).
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Fig. 12B —35-year-old woman with ankylosing spondylitis:
postinflammatory sacroiliac sclerotic changes after acute sacroiliitis. Axial
(A) and gadolinium-enhanced fat-saturated (B) T1-weighted images
of sacroiliac joints show subchondral hypointensity indicative of sclerotic
changes (arrows).
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Fig. 13 —35-year-old woman with ankylosing spondylitis:
postinflammatory sacroiliac sclerotic changes after acute sacroiliitis. Axial
CT scan shows condensations of subchondral bone marrow of joints
(arrows) predominant on left side.
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Fig. 14A —53-year-old woman with ankylosing spondylitis: sacroiliac
joint ankylosis. Axial CT scan (A) and volume reformation, frontal view
(B) of sacroiliac joints show complete ankylosis with homogeneous
osseous bridge passing through articulations (arrowheads).
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Fig. 14B —53-year-old woman with ankylosing spondylitis: sacroiliac
joint ankylosis. Axial CT scan (A) and volume reformation, frontal view
(B) of sacroiliac joints show complete ankylosis with homogeneous
osseous bridge passing through articulations (arrowheads).
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Conclusion
Although radiographs are usually first obtained for the detection of axial
involvement in spondyloarthropathies, CT and MRI are more sensitive and
specific, allowing earlier diagnosis and optimized management of affected
patients. Because earlier treatment may be associated with a better prognosis,
radiologists should be familiar with the wide spectrum of imaging findings,
particularly during the early stages of inflammation.
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Abstract
Introduction
