“Sticky Spine”: A Review of the Imaging Findings for Spinal Arachnoiditis

Arachnoiditis is caused by inflammation of the meninges and subarachnoid space, and when it affects the cauda equina, it is referred to as adhesive or spinal arachnoiditis. The pathophysiology is related to an inflammatory process that results in adherence of the nerve roots to each other and the dura. Patients can experience chronic and persistent back pain, though some cases can present with neurologic impairment. MR imaging is the imaging technique of choice for the evaluation of these patients and enables the classification of arachnoiditis into 3 patterns based on its appearance: 1) the nerve roots are clumped together and distorted; 2) the nerve roots are adherent to the periphery of the thecal sac, creating the empty thecal sac sign; and 3) a large central soft-tissue mass replaces the thecal sac. Rarely, chronic inflammation and fibrosis can occur, leading to arachnoiditis ossificans. Recognition of the neuroimaging findings in the different phases of the inflammatory process and its precise description is essential to clinical counseling and surgical treatment planning.Learning Objectives: To review the pathophysiology and classification of arachnoiditis, to describe the clinical presentations and their imaging characteristics, and to discuss its main complications