Facet joint gouty arthropathy
Low back pain following a fall.
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Diffuse osteopenia. There is a well defined hyperdense mass with irregular margins centered at the right L5/S1 facet joint, causing osseous destruction (although the bony margins appear corticated), extending to the central canal and right sided L5 neural exit foramen, effacing the right sided epidural fat within the central canal. The mass compresses the L5 nerve root within the neural foramen but appears separate to it. It is also seen to abut the descending S1 nerve root on the right. There is also mild extension into the right sided paravertebral muscle posteriorly. The mass measures 38x18x37mm in size. No convincing internal calcification. No further mass lesion is identified. The vertebral body heights are preserved. No acute fracture is identified. Limited views of the abdomen demonstrates ascites and evidence of presumed previous left sided nephrectomy. Uncomplicated diverticulosis.
Conclusion: No acute intracranial abnormality. The well-defined hyperdense abnormality/mass centred at the right L5/S1 facet joint with secondary osseous destruction is most consistent with a gouty thophus. The L5 nerve root is compressed within the right L5 neural exit foramen and there is also likely compression of the descending right S1 nerve root. Large volume ascites and presumed previous left-sided nephrectomy.
The patient had markedly raised serum uric acid and known gouty arthropathy in multiple joints.
Core biopsies of the abnormality were performed showing monosodium urate crystals.