Spinal synovial cyst
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There are 5 lumbar-type vertebrae and the iliolumbar ligament attaches to L5. Posterior fusion at L5/S1. L5 pars defects and anterolisthesis L5 on S1, degree of anterior displacement is stable measuring 6 mm. there is also bilateral pars defects without displacement at L3, best seen on the previous CT from 4 years ago. No abnormal vertebral body marrow signal.
Marked narrowing of the lumbar and upper sacral thecal sac secondary to epidural lipomatosis again noted, essentially stable in severity. This causes absence of CSF between the cauda equina nerve roots.
There is a new T2 hyperintense and T1 hypointense non-enhancing cystic lesion in the right posterior epidural space at the upper L3 vertebral body level. It measures 8 mm maximum diameter axially and 11 mm longitudinally and displaces the narrowed thecal sac anteriorly and to the left. The adjacent facet joint appears degenerative and there is no definite connection between the joint and the cystic lesion.
The conus has a normal appearance and terminates at the L1 level.
New right posterior epidural cystic lesion at the upper L3 level, displacing the narrowed thecal sac and cauda equina. This likely represents a synovial cyst arising from the adjacent facet joint however a definite connection is not well appreciated. A cystic neoplasm warrants consideration but is thought less likely.
A synovial cyst was confirmed at surgery.