Arachnoiditis ossificans is an unusual chronic meningeal inflammatory process and is thought to be the sequela of end-stage adhesive arachnoiditis.

Common causative factors include surgery, arachnoid hemorrhage, myelography (particularly oil-based contrast agents), and spinal anesthesia.

CT and MRI are complementary imaging techniques. 

CT is the best investigation tool to visualize the ossified intraspinal lesion and nerve roots. The findings of ossified intrathecal lesions are specific and diagnostic. As in this case, there is curvilinear dural calcifications, intrathecal coarse calcifications and ossified individual nerve roots adhered to the posterior thecal sac.

The MR imaging is favorable in depicting arachnoiditis. The sign includes central clumping of nerve roots, peripheral adhesion of the nerve roots and intradural cysts due to loculation of the subarachnoid spaces.