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| ORIGINAL CONTRIBUTION - RHEUMATOLOGY |
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| Year : 2016 | Volume
: 2
| Issue : 4 | Page : 179-184 |
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Comparison of radiography, computed tomography and magnetic resonance imaging in the detection of sacroiliitis in ankylosing spondylitis
Anju Ranga1, Yatish Agarwal1, Virendra K Meena1, RK Chopra2
1 Department of Radio.diagnosis, VMMC and Safdarjung Hospital, New Delhi, India
2 Central Institute of Orthopaedics, VMMC and Safdarjung Hospital, New Delhi, India
| Date of Web Publication | 22-Sep-2016 |
Correspondence Address:
Anju Ranga
Room Number 23, H-block, Department of Radio.diagnosis, VMMC and Safdarjung Hospital, New Delhi - 110 029
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2349-0977.191042
Objective: The objectives of our study were to evaluate the role of conventional radiography, computed tomography (CT), and magnetic resonance imaging (MRI) in the detection of sacroiliitis in ankylosing spondylitis (AS), along with the radiological spectrum of disease. Materials and Methods: Thirty-six patients with symptoms of inflammatory back pain (IBP) were evaluated with conventional radiography, CT, and MRI. The sacroiliac (SI) joints were evaluated for joint margins, joint space, sclerosis, and bone marrow changes. Imaging findings were analyzed for correlation with multiple clinical characteristics and comparison among different imaging modalities. Results: CT and MRI are extremely useful in the absence of alterations or minimal changes on plain radiographs. CT is comparable to MRI for joint space alteration, however, itis superior for evaluating bone sclerosis and erosion, and is indicated especially for detecting chronic alterations. The capability of MRI to distinguish between acute and chronic changes and estimate the degree of disease activity and damage present at diagnosis can be beneficial in monitoring the effect of pharmacological treatment. The administration of Gadolinium did not provide any additional information for the diagnosis of sacroiliitis and the evaluation of the features of active inflammation. Conclusions: Between radiography, CT and MRI, MRI outscores the others in being able to delineate the inflammatory changes of early sacroiliitis in AS. Therefore, if early sacroiliitis is suspected clinically, MRI should be the preferred imaging modality for evaluating the SI joint. However, CT is more sensitive than radiography and MRI in detailing the structural changes of sacroiliitis in AS. Keywords: Ankylosing spondylitis, CT, MRI, sacroiliitis
How to cite this article:
Ranga A, Agarwal Y, Meena VK, Chopra R K. Comparison of radiography, computed tomography and magnetic resonance imaging in the detection of sacroiliitis in ankylosing spondylitis. Astrocyte 2016;2:179-84 |
How to cite this URL:
Ranga A, Agarwal Y, Meena VK, Chopra R K. Comparison of radiography, computed tomography and magnetic resonance imaging in the detection of sacroiliitis in ankylosing spondylitis. Astrocyte [serial online] 2016 [cited 2023 Dec 6];2:179-84. Available from: http://www.astrocyte.in/text.asp?2016/2/4/179/191042 |
| Introduction | |  |
Spondyloarthropathy comprises a group of chronic inflammatory rheumatic diseases, including ankylosing spondylitis (AS), reactive arthritis (Reiter syndrome), arthritis or spondylitis associated with inflammatory bowel disease, and psoriatic arthritis, as well as undifferentiated spondyloarthritis.[1] These afflictions predominantly affect the axial skeleton, causing pain and stiffness;[2] are seronegative for rheumatoid factor; and are often associated with the presence of human lymphocyte antigen (HLA) B27.[3] They are largely differentiated on the basis of clinical information and the distribution of radiographic abnormalities.[4] The sacroiliac (SI) joints are involved in most cases of axial spondyloarthropathy, the first manifestation usually being sacroiliitis.[5],[6] A finding of sacroiliitis at radiography is the classic diagnostic hallmark of axial spondyloarthropathy.
AS is a chronic, disabling rheumatic disease characterized by IBP, restricted spinal mobility, and frequently peripheral arthritis, enthesitis, and acute anterior uveitis. The disease usually begins in the second or third decade, and demonstrates a striking male preponderance of 3:1 over females.[1] With an estimated prevalence of 1.3% in the Indian population, AS carries a significant health burden for the community.[7] Symptoms commonly begin in late adolescence and early adulthood, which are the most productive years of life. If undiagnosed or inadequately untreated, the disease produces continuous pain, stiffness, fatigue, and progressive loss of spinal mobility and function, leading to a reduction in the quality of life.
An unacceptably long delay of 8–11 years between the onset of symptoms and the time of diagnosis has been reported in AS.[8] Until recently, treatment options for AS were limited with conventional disease-modifying anti-rheumatic drugs that carry limited effect on spinal inflammation. This clinical scenario has now changed. The newer antitumor necrosis factor (TNF) agents offer exciting possibilities for effective treatment and possible arrest of the disease progression.[9]
At present, imaging is essential for the diagnosis of AS for the purpose of identifying the presence of sacroiliitis. Conventional radiographs, computed tomography (CT), and magnetic resonance imaging (MRI) are the currently available imaging modalities to evaluate sacroiliitis. Despite the use of these different modalities, difficulties in diagnosing sacroiliitis persist. Plain radiography is always the initial method for evaluating the SI joints but its accuracy is limited by the lack of sensitivity in early stages of the inflammation. By using CT, sclerosis and ankylosis can easily be diagnosed, and for the detection of bony changes, CT can be superior to MRI. However, the pendulum is increasingly shifting in favor of MRI, which can identify abnormalities that are thought to reflect inflammatory disease activity in the joint and subchondral bone.
In this study, wecompared the results of conventional radiography, CT and MR, highlighting the significance of each inimaging the SIjoints in patients with early AS.
Aim
To compare radiography, CT, and MRI in the detection of sacroiliitis in AS.
Objectives
- To study the role of conventional radiography, CT, and MRI in detection of sacroiliitis in AS
- To study the radiological spectrum in ASand to assess if demographic variables, namely age and gender, and the duration of symptoms, have a substantive effect on disease-related changes.
| Materials and Methods | | |
This cross-sectional observational study was conducted over a period of 18 months between November 2012 and April 2014 in the Department of Radiodiagnosis in collaboration with the Central Institute of Orthopaedics and Department of Physical Medicine and Rehabilitation at Safdarjung Hospital, New Delhi, which is a tertiary care public teaching hospital located in the metropolis of Delhi catering to both the urban and rural population of New Delhi and neighboring states.
Patients with low back pain and morning stiffness of more than 30 min, with improvement in symptoms with exercise but not with rest, exhibiting good response to nonsteroidal anti-inflammatory drugs, and of age less than 45 years at onset of pain were included in the study.
Patients excluded from the study included those with contraindications to an MR evaluation, such as presence of pacemakers, claustrophobia, metallic implants; contraindication to intravenous MR contrast material; inability to restrain movement during the course of examination even after appropriate sedation; pregnant women; and any patient with evidence or clinical history of metabolic disease, malignancies and positive rheumatoid factor.
Each patient was counseled and an informed consent was obtained. Each patient was evaluated as per a predesigned proforma which recorded the demographic profile, presenting complaints, if any, family history, significant past history, and a detailed physical examination.
Each patient underwent radiographs, CT, and MRI studies ofSI joints in the following predetermined formats. Radiographs of both SI joints were taken in posteroanterior (PA) and oblique projections. The PA view was taken in the prone position with the tube angled 10 to 25 degrees toward the head. The oblique view was taken in the supine position with the patient raised so that the antero-posterior axis of the pelvis made an angle of 15 to 25 degrees to the horizontal, and the tube was angled 15° toward the head.
NoncontrastCT (NCCT) was performed in supine position with 25–30 cranial gantry tilt to obtain semicoronal images through both the cartilaginous and ligamentous portions of the SIjoint using the 40-slice CT scanner: Philips brilliance 40 in the department. For image reconstruction, a high resolution algorithm was used.
The following findings were specifically considered in relation to AS: Joint surface erosions, increased/decreased/ankylosed joint space (normal joint space = 2.49 ± 0.66 mm in people under 40 years of age and 1.47 ± 00.21 mm in older people [10],[11]); bone marrow sclerosis; change in bone density (decreased density being a marker of fat accumulation in the bone marrow);and irregular surface or new bone formation at entheses.
MRI study was performed on 1.5 T Philips achieva Scanner using a dedicated sense body coil. Images were obtained in following sequences in oblique axial and coronal planes: TR/TE/TI 4000/30/150ms for short TI inversion recovery (STIR); TR/TE 405/12ms forT1; TR/TE 660/12ms for fat-suppressed T1; and TR/TE 4100/132ms for T2. Post-gadolinium administration (dose 0.1mmol/kg), enhanced fat-suppressed-T1-weighted (T1W)(TR/TE 660/16ms) imaging was also performed. The slice thickness was 4mm in all sequences with a spacing of <1mm. The following findings were especially considered on the MR examination: Bone marrow edema (high signal intensity at STIR), gadolinium contrast enhancement in the cartilaginous and ligamentous joint space, gadolinium contrast enhancement at entheses outside the joint, fat accumulation in bone marrow (high signal intensity at T1, suppressed on STIR), change in joint space width, irregular surface, or new bone formation at entheses, erosions, and osseous sclerosis (low signal intensity at T1 and T1 fat suppressed).
Statistical evaluation
The data pertaining to diverse morphological characteristics, that is, osseous changes, changes in joint margins, changes in joint space, and abnormalities at entheses on conventional radiography, CT, and MRI were analyzed in relation to age brackets and gender of the subjects, as well as the total duration of their symptoms.
The collated data were analyzed to determine if a temporal relationship exists between the morphological characteristics and the ability of conventional radiography, CT, and MRI in identifying them.
| Observations and Results | | |
Demographic and clinical data
The patient population included 31 men and 5 women with a mean age of 26 years (range: 15–38). The gender distribution in this study shows a higher incidence in males with a male: female ratio of 6.2:1[ [Table 1]. | Table 1: Demographics, clinical features, and laboratory findings in the study cohort
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All cases presented with low back pain and morning stiffness and 80.56% cases showed improvement in symptoms with exercise. Family history in first degree relatives was present in 47.22% cases.
CRP (c-reactive protein) and ESR (erythrocyte sedimentation rate) values were raised in 25 (69.44%) and 29 (80.56%) cases, respectively. Findings for HLA-B27 were positive in 26 (72.22%) patients.
Joint margin
In this study, CT detected erosions in 20 cases (55.56%), MRI detected erosions in 11 cases (30.56%), where as X-ray detected erosions in only 1 case (2.78%). CT and MRI were significantly better techniques (P < 0.005) than X-ray in evaluating joint erosions. Among CT and MRI, CT was a better imaging modality (P < 0.005).
Joint space
CT detected increased joint space in 6 cases (16.67%), decreased joint space in 12 cases (33.33%), and ankylosisin only 1 case (2.78%). MRI detected increased joint space in 3 cases (8.33%), decreased joint space in 12 cases (33.33%), and ankylosis in 1 case (2.78%) only. X-ray detected increased joint space in only 1 case (2.78%), decreased joint space in 3 cases (8.33%), and ankylosisin only 1 case (2.78%).
CT and MRI were better than X-ray for joint space evaluation (P < 0.05). There was no significant difference between CT and MRI for joint space abnormality evaluation.
Sclerosis
In present study, CT detected sclerosis in 18 cases (50.00%), MRI detected sclerosis in 9 cases (25.00%) where as X-ray detected sclerosis in 8 cases (22.22%) [Table 2]. | Table 2: Comparison of X-ray, CT, and MRI in detection of joint abnormalities
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Among CT, MRI, and X-ray, CT was the best modality for evaluation of sclerosis. Statistically significant difference was not seen between MRI and X-ray for sclerosis evaluation.
Bone marrow changes on magnetic resonance imaging
Signal intensity of bone marrow was decreased on T1W sequence and increased on T2/STIR sequence in 23 cases (63.89%) and 30 cases (83.33%), respectively. Contrast enhancement after intravenous gadolinium administration was seen in bone marrow in 30 cases (83.33%) and in joint space in 18 cases (50.00%). Only 12 cases (33.33%) had fat accumulation in bone marrow [Table 3]. Two interesting cases have been illustrated in [Figure 1]and [Figure 2]. | Figure 1: Radiographs in PA (a) and B/L oblique views (b-right, c-left) show normal sacroiliac joint (black arrows). NCCT axial image (d) of bilateral SI joint appears normal (black arrows). Coronal STIR MR image (e) shows multiple hyperintensities (black arrows) in the inferior portion of bilateral SI joint. Axial fat-suppressed post-contrast T1-weighted MR image (f) shows contrast enhancement (black arrows) in bilateral SI joint.
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 | Figure 2: X-ray bilateral SI joint in PA view (a) shows sclerosis of bilateral SI joint (black arrows). NCCT coronal image (b) shows multiple erosions and sclerotic changes mainly in inferior portion of bilateral iliac bones (black arrows). Coronal STIR MRI image (c) shows multiple hyperintensities in bilateral SI joint in inferior sacral portion (white arrows). Coronal post-contrast fat-suppressed T1-weighted MR image (d) shows contrast enhancement in bilateral SI joint predominantly in inferior sacral portion (white arrows).
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Duration of disease
Duration of symptoms was less than 1 year in 10 cases (27.78%), and in these cases, changes of sacroiliitis were detected only on MRI [Chart 1 [Additional file 1]].
In 22 (61.11%) cases, duration of symptoms was more than 1 year and in these cases, changes of sacroiliitis could be detected on all imaging modalities combined, i.e. X-ray, CT, and MRI, or only on CT and MRI.
| Discussion | | |
Given the progressive and debilitating nature of the disease and development of new promising treatment options, it is important to diagnose AS early, detect active sacroiliitis and differentiate it from chronic changes, and monitor for potential changes after therapy.
The modified New York criteria [12] require combination of clinical symptoms and radiological findings to diagnose AS.
The clinical symptom of IBP has been recognized as a cardinal symptom for AS for years, and assessment requires neither laboratory tests nor radiographic studies.[1] It has been estimated that when symptoms of IBP are present in a patient with chronic low back pain, the post-test probability for having the diagnosis of axial spondyloarthropathy is 14%. Recent refinement of these clinical features has identified a candidate core set of criteria for IBP: (1) morning stiffness of >30 min, (2) improvement in back pain with exercise but not with rest, (3) awakening because of back pain during the second-half of the night only, and (4) alternating buttock pain.[12],[13]
Currently available imaging modalities to evaluate sacroiliitis include conventional radiographs, CT, and MRI.
Radiography is the most widely accepted imaging method for diagnosing sacroiliitisbecause it is relatively inexpensive, readily available, and, when it yields positive findings, is very helpful.
Although conventional X-ray remains the most utilized imaging method in the clinical practice, an international consensus still remains to be reached regarding the best technique and view for radiographic evaluation of the SI joint. PA views, with 10–15°cranial tilt of X-ray tube, and oblique views are the most utilized in our practice in an attempt to minimize structures overlapping, thus facilitating the study interpretation.
The main limitation of the X-ray film is the low sensitivity for detecting abnormalities in the early stages of the disease. Radiographic signs of sacroiliitis appear only three to seven years after the initial symptoms onset, presenting with alterations only in the chronic phase of the disease. Furthermore, radiographs are difficult to interpret, intra-and inter-observer correlation is low, and active inflammation cannot be assessed.
The main radiographic signs are bone erosions, joint space alterations, subchondral sclerosis, and ankylosis. According to the modified New York criteria, five grades—from 0 (normal) to 4 (ankylosis)—can be differentiated. Grade 0 denotes normal SI joints with well-defined margins; grade 1, suspicious changes with incipient sclerosis and decreased focal thickness of the articular space; grade 2, minimal abnormality with loss of definition of the articular margins, subchondral osteoporosis, and areas of reactive sclerosis; grade 3, unequivocal abnormality with subchondral sclerosis of both sacral and iliac articular margins (predominantly on the iliac side), erosions, reduced articular space, widening of the joint space, and incipient ankylosis; and grade 4, complete ankylosis with residual sclerosis, which tends to decrease over time. On the basis of the modified New York criteria, bilateral changes corresponding to grade 2 or higher, or unilateral changes corresponding to grade 3 or higher, must be detected to diagnose sacroiliitis radiographically.[11]
CT and MRI are extremely useful in the absence of alterations, or minimal changes on plain radiographs. The evaluation of sacroiliitis by CT, in comparison with the conventional X-ray, has shown to be more sensitive, with a better and early detection of bone alterations, principally because of its capability to perform sequential slices, thus avoiding structures to overlap.
In the present set of patients, the CT showed higher sensitivity for detecting minimal bone erosions and joint space narrowing, however, presentedthe same diagnostic capacity of plain X-rays in cases of ankylosis. CT is comparable to MRI for joint space alteration but is superior for evaluating bone sclerosis and erosion and is indicated especially for detecting chronic alterations.
On the other hand, SI joint evaluation by CT presents some inconveniences such asradiation exposure and incapacity to show alterations in the acute phase, identifying the inflammatory consequences rather than the inflammatory process activity.
A 2003 workshop on sacroiliitis proposed a grading system for CT findings in which Grade IA denotes a SI joint articular space greater than 4 mm; Grade IB, a SI joint space less than 2 mm; Grade IIA, contour irregularities; Grade IIB, erosions (appearing early in the iliac aspect and later on the sacral side); Grade IIIA, significant subchondral sclerosis; Grade IIIB, spur formation; Grade IVA, transarticular bone bridges; and Grade IVB, total ankylosis.[14]
MRI has been suggested as the method of choice in the evaluation of sacroiliitis, because of the higher quality of the images, absence of ionizing radiation, and the capacity of detecting and differentiating acute and chronic alterations.
Main alterations seen on MRI inpatients with sacroiliitis are:
- Subchondral bone marrow edema characterized by low intensity signal on T1 and high intensity signal on T2W fat-saturated and STIR sequences. Significant enhancement of SI joint and surrounding bone marrow observed on post-gadoliniumT1W fat-saturated sequences is highly suggestive of an active disease
- Subchondral sclerosis characterized by zones with low-intensity signal on T1W and T2W images
- Cortical bone erosions represented by foci with intermediate signal intensity on T1W and T2W sequences in sacral or iliac cortical bone, with marginal irregularity and deeper defects, also affecting the adjacent bone marrow. These erosions are better demonstrated on T1Wfat-saturated sequences.
The advantages of MRI compared to CT and radiography in evaluating sacroiliitis include detection of bone marrow edema and detection of contrast enhancement. The capability of MRI to distinguish between acute and chronic changes and to estimate the degree of disease activity and damage present at diagnosis can be beneficial in monitoring the effect of pharmacological treatment.
To our knowledge, few studies comparing MR, CT, and radiography of the SI joint with regard to sacroiliitis have been published.[15],[16],[17],[18],[19],[20] The number of patients included in these studies varied from 17 to 50. The duration of symptoms was mentioned in only one of these studies. Most of the studies included patients who had defined AS. Therefore, it seems likely that our patients were examined at an earlier stage of the disease because they had a relatively short duration of symptoms.
Gadolinium enhancement in the joint space was found in 50% of cases. Bone marrow edema was present in 83.33% cases in which contrast enhancement was also seen. All the areas of bone marrow enhancement or joint space enhancement produced high signal intensity on the STIR sequence. Therefore, the administration of Gadolinium did not provide any additional information for the diagnosis of sacroiliitis and the evaluation of features of active inflammation.
| Conclusion | | |
Between radiography, CT, and MRI, MRI outscores the others in being able to delineate the inflammatory changes of early sacroiliitis in AS. These changes, which include bone marrow edema and enhancement of joint space, cannot be demonstrated on radiography or CT. Therefore, if early sacroiliitis is suspected clinically, MRI should be the preferred imaging modality for evaluating the SI joint.
However, CT is more sensitive than radiography and MRI in detailing the structural changes of sacroiliitis in ankylosing spondylitis. These changes include the presence of erosions and sclerosis in the affected joint margins.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]
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