PMC7206789_01
a A 32-yo male Pacific Islander with probable gouty tophi affecting both hands (red arrows). b Lumbar spine MRI (T2, axial view) image reported as showing an abscess surrounding the right L4/5 facet joint (red arrow). Axial CT image of lumbar spine showing c erosions (white arrow); and d corresponding DECT image (Siemens Somatom Force ) showing monosodium uric acid crystal deposition (green)
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Fig1
On examination, he was febrile at 38.5  C with multiple probable tophi on the dorsum of both hands (Fig. 1a). Magnetic resonance imaging (MRI) of the spine to investigate the severe back pain was reported as showing right L4/5 facet joint septic arthritis with abscess formation (Fig. 1b). A DECT was performed to assess the extent of MSU crystal deposition in the spine (Fig. 1c, d). This showed multiple well-defined focal erosions at the right L3/4, L4/5 and L5/S1 facet joints, with dual energy attenuation characteristic of MSU deposition (Fig. 1c and d).
PMC7206789_02
a Axial CT image showing right L4/5 facet joint erosion (white arrow) with calcified peri-articular mass encroaching on lumbar canal (dashed white arrow), and b corresponding DECT image (Siemens Somatom Force ) showing monosodium uric acid crystal deposition (green). c Sagittal T2-fat suppressed MRI image (General Electric 1.5 T Signa Excite ) of the lumbar spine showing the soft tissue mass seen in a and b causing marked lumbar canal stenosis, and d corresponding DECT image (Siemens Somatom Force ) showing attenuation consistent with monosodium uric acid crystal deposition
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Fig2
A CT and MRI scan of the lumbar spine showed an erosive arthropathy involving the right L4/L5 facet joint associated with a partially calcified peri-articular mass causing marked spinal canal stenosis and compression of the descending right L5 nerve root (Fig. 2a and c).  Given the history of chronic renal disease and presence of peripheral tophi, DECT was performed which demonstrated attenuation of the soft tissue mass at the right L4/5 facet joint consistent with MSU deposition (Fig. 2b and d).