Arachnoiditis is a broad term denoting inflammation of the meninges and subarachnoid space. It is characterized by thickening of the arachnoid membrane and dura mater adhesions that result in chronic lower back pain. Complications include cranial neuropathies, myelopathy, and radiculopathy.
Arachnoiditis has many causes, including infectious, inflammatory, and neoplastic processes. Infectious causes include bacterial, viral, fungal, and parasitic agents. Noninfectious inflammatory etiologies include surgery, intrathecal hemorrhage, and the administration of intrathecal agents, such as myelographic contrast media, anesthetics, and steroids.
The most severe type of arachnoiditis is adhesive arachnoiditis, with scar tissue compressing the nerve roots and ultimately disrupting both blood supply and flow of cerebrospinal fluid. Adhesive arachnoiditis can progress to arachnoiditis ossificans, or ossification of the spinal arachnoid.
Neoplasia includes the hematogenous spread of systemic tumors, such as breast and lung carcinoma, melanoma, and non-Hodgkin lymphoma. Neoplasia also includes direct seeding of the cerebrospinal fluid (CSF) from primary central nervous system (CNS) tumors, such as glioblastoma multiforme, medulloblastoma, ependymoma, and choroid plexus carcinoma.
Because of its noninvasive nature, multiplanar capabilities, and superb soft-tissue characterization, magnetic resonance imaging (MRI) is the study of choice for the diagnostic evaluation of arachnoiditis.
For patients in whom MRI is contraindicated, computed tomography (CT) myelography is an acceptable alternative.
Neural effects of arachnoiditis are demonstrated in the images below.
Postoperative anteroposterior (AP) myelogram reveals thickened, clumped nerve roots in arachnoiditis.
Sagittal T1-weighted MRI of the lumbar spine in a patient with adhesive arachnoiditis who received epidural steroid injections. Image shows thickened and clumped nerve roots, which give the appearance of a tethered spinal cord.
Axial T1-weighted MRI of the lumbar spine shows that the nerve roots adhere to one another and the dural sac.