Several studies have shown CT to have higher sensitivity for detection of sacroiliitis than radiography [43,44,47,55]. Low-dose CT is increasingly being performed and can demonstrate the fine structural changes of axSpA better than radiography [45]. Additionally, the interreader reliability has shown to be excellent for grading sacroiliitis on CT, higher than for radiography, because of the increased level of structural detail demonstrated by CT [47]. Although conventional CT has the ability to demonstrate the chronic structural changes of sacroiliitis, it cannot demonstrate active inflammation, and therefore MRI remains the technique of choice for the diagnosis of axSpA [1,3,19,22]. There is evolving literature on the use of dual-energy CT (DECT) in the evaluation of sacroiliitis in axSpA, with early studies showing the ability of DECT to demonstrate bone marrow edema in patients with axSpA in addition to the inherent ability of CT to demonstrate the chronic structural changes of sacroiliitis [56,57]. One study shows that DECT has a sensitivity of 87% to 93% and specificity of 91% to 94% for detection of bone marrow edema using MRI as the reference standard, but more data are needed to support the diagnostic utility of DECT in the evaluation of axSpA [56]. There is no role for intravenous (IV) contrast in CT evaluation of axSpA. CT Sacroiliac Joints and Spine Area of Interest CT demonstrates structural changes in the sacroiliac joints and spine in patients with axSpA that may not be apparent on radiographs [22]. These structural changes include erosions, sclerosis, bone formation, syndesmophytes, and ankylosis [49,54]. In addition to its diagnostic utility in assessment of the sacroiliac joints, CT of the spine has the ability to demonstrate syndesmophytes with higher sensitivity than radiographs, and low-dose protocols can be utilized [58].
Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Several studies have shown CT to have higher sensitivity for detection of sacroiliitis than radiography [43,44,47,55]. Low-dose CT is increasingly being performed and can demonstrate the fine structural changes of axSpA better than radiography [45]. Additionally, the interreader reliability has shown to be excellent for grading sacroiliitis on CT, higher than for radiography, because of the increased level of structural detail demonstrated by CT [47]. Although conventional CT has the ability to demonstrate the chronic structural changes of sacroiliitis, it cannot demonstrate active inflammation, and therefore MRI remains the technique of choice for the diagnosis of axSpA [1,3,19,22]. There is evolving literature on the use of dual-energy CT (DECT) in the evaluation of sacroiliitis in axSpA, with early studies showing the ability of DECT to demonstrate bone marrow edema in patients with axSpA in addition to the inherent ability of CT to demonstrate the chronic structural changes of sacroiliitis [56,57]. One study shows that DECT has a sensitivity of 87% to 93% and specificity of 91% to 94% for detection of bone marrow edema using MRI as the reference standard, but more data are needed to support the diagnostic utility of DECT in the evaluation of axSpA [56]. There is no role for intravenous (IV) contrast in CT evaluation of axSpA. CT Sacroiliac Joints and Spine Area of Interest CT demonstrates structural changes in the sacroiliac joints and spine in patients with axSpA that may not be apparent on radiographs [22]. These structural changes include erosions, sclerosis, bone formation, syndesmophytes, and ankylosis [49,54]. In addition to its diagnostic utility in assessment of the sacroiliac joints, CT of the spine has the ability to demonstrate syndesmophytes with higher sensitivity than radiographs, and low-dose protocols can be utilized [58].