Presentation
A 70-year-old kyphotic male patient presented with low back pain.
Patient Data
Spine: diffuse syndesmophytic ankylosis can give a "bamboo spine" appearance, interspinous ligament ossification can give a "dagger spine" appearance
Sacroiliac joint: no narrowing of the synovial portion.
Hips: bilateral and symmetric uniform joint space narrowing with axial migration of the femoral head causing protrusio acetabuli, with a collar of osteophytes at the femoral head-neck junction more evident on the left side.
Spine: nearly fused spine having the characteristic appearance of a "bamboo spine". Interspinous ligament ossification "dagger spine" appearance is clearly seen at the VR images.
Reduced bone density.
Facet joint arthropathy is seen.
Incontinuity of the ossified anterior longitudinal ligament is seen at D12/L1 level, may represent chalk stick or carrot stick fractures. Vacuum phenomenon is seen at the same level.
Ossification of the intervertebral discs is also evident.
Sacroiliac joint: Sparing of the synovial portion of sacroiliac joint with calcification of the bridging sacroiliac ligament.
Spondylodegenerative changes of the lumbar spine with fatty degeneration of the vertebral endplates.
Secondary canal stenosis at T12/L1 level.
Diffuse disc bulges at L3/L4, L4/L5 and L5/S1 levels indenting the thecal sac and both nerve roots.
The high signal intensity on T1W images may be due to the presence of immature calcium.
Case Discussion
Diffuse idiopathic skeletal hyperostosis (DISH) is a condition where there is flowing ossification of the anterior longitudinal ligament involving the thoracic spine and enthesopathy (e.g. at the iliac crest, ischial tuberosities, and greater trochanters). There is no involvement of the sacroiliac synovial joint.
Ankylosing spondylitis (AS) is a very close differential diagnosis, however, the following points favor the diagnosis of diffuse idiopathic skeletal hyperostosis:
- old age of the patient (AS involves the middle-aged males)
- bulky syndesmophytes
- sparing the synovial portion of sacroiliac joint (they are ankylosed in AS)
- calcification of the bridging sacroiliac ligament (typical of DISH)
Chalk stick or carrot stick fractures are fractures of a fused spine, classically seen in diffuse idiopathic skeletal hyperostosis and ankylosing spondylitis.
The hyperintense signal of intervertebral discs may be due to the presence of mobile protons (liquid state or milk of calcium) in calcium 1.
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