Adhesive arachnoiditis causing cauda equina syndrome in ankylosing spondylitis: CT anti MRI demonstration of dural calcification and a dorsal dural diverticulum

We present the radiological features of a 42-year-old man with long-standin g inactive ankylosing spondylitis (AS), demonstrating that arachnoiditis is a cause of a cauda equina syndrome (CES) in this disease. CT showed a dors al arachnoid diverticulum causing scalloped erosion of the laminae, and pun ctate and curvilinear dural calcification. MRI revealed adhesion and conver gence of the cauda equina dorsally into the arachnoid pouch, causing the du ral sac to appear empty canal. To the best of our knowledge, dural calcific ation on CT is a new finding in AS, which may be related to the CES. Our fi ndings support the hypothesis that chronic adhesive arachnoiditis with subs equent loss of meningeal elasticity may be the main cause of CES in AS.