Ankylosing Spondylitis, Radiologic Perspective (cont.)
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Radiologic Diagnosis of Ankylosing Spondylitis
Radiographs (plain X-ray films) are the single most important imaging technique for detection, diagnosis, and follow-up monitoring of patients with ankylosing spondylitis. Overall, X-ray films can well depict bony features, subtle deposits of calcium in tissue, and areas of tissue that are hardening into bone. The doctor can reliably diagnose ankylosing spondylitis if its typical radiographic features are present.
Radiographic findings are as follows:
Computed tomography (CT) may be useful in selected patients in whom ankylosing spondylitis is suspected and in whom initial sacroiliac joint X-ray film findings are normal or inconclusive. Features such as joint erosions and bony ankylosis are easier to see on CT scans than on X-ray films.
CT supplements a diagnostic procedure called bone scintigraphy, which involves injecting a radioactive material into the body and tracking the activity of the material. CT helps the doctor evaluate areas of increased uptake of the radioactive material, particularly in the spine. Bony lesions, such as pseudoarthrosis, fractures, spinal canal narrowing, and facet inflammatory disease can be detected using CT.
Magnetic Resonance Imaging
Advantages of magnetic resonance imaging (MRI) include direct visualization of cartilage abnormalities, detection of bone marrow edema (an abnormal buildup of fluid), improved detection of erosions, and safety from possible radiation hazards.
MRI may have a role in the early diagnosis of sacroiliitis. The detection of synovial enhancement at MRI has been found to correlate with disease activity as measured by laboratory tests. MRI has been found to be superior to CT in the detection of cartilage, bone erosions, and bone changes beneath the cartilage. MRI is also sensitive for assessment of activity early in the course of ankylosing spondylitis and may have a role in monitoring the treatment of patients with active ankylosing spondylitis.
In long-standing ankylosing spondylitis, MRI detects pseudoarthrosis, diverticula associated with cauda equina syndrome (severe compression of nerves at the bottom of the spinal cord), and spinal canal stenosis (narrowing or constriction). In patients with fracture complications or pseudoarthrosis, MRI is useful for assessment of spinal canal narrowing and cord injury. MRI is considered to be mandatory in patients with neurologic symptoms, especially in those with neurologic deterioration after established spinal cord injury.
Scintigraphy has been used to detect early sacroiliitis, but conflicting results have been reported concerning its accuracy. An increase in the uptake of radioactive material by bone based on bone scintigraphy findings may also be used to evaluate active ankylosing spondylitis. Sites affected include the limb joints and entheses. An important application is the evaluation of patients with long-standing ankylosing spondylitis who develop new pain with or without a recent history of trauma. Focal areas of radioactive material uptake may indicate a fracture or pseudoarthrosis.
Medically Reviewed by a Doctor on 7/18/2016
Wilfred CG Peh, MD, MBBS, FRCP(Edin), FRCP(Glasg), FRCR, MHSM
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