Introduction
Background
Arachnoiditis is a broad term denoting inflammation of the meninges and subarachnoid space. A variety of etiologies exist, including infectious, inflammatory, and neoplastic processes.
Infectious etiologies include bacterial, viral, fungal, and parasitic agents. Noninfectious inflammatory processes include surgery, intrathecal hemorrhage, and the administration of intrathecal agents such as myelographic contrast media, anesthetics, and steroids.
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.
Pathophysiology
Infection may spread to the meninges by means of dissemination through the subarachnoid space, as with intracranial tuberculous meningitis; by means of intraspinal extension of a discitis and/or osteomyelitis; or by means of hematogenous spread from a source outside the CNS.
Pathologically, subarachnoid infection produces meningeal inflammation that leads to congestion and inflammatory exudate. Adhesions form between fibrin-coated nerve roots and meninges, causing them to adhere to one another. Subsequently, adhesions containing collagen are formed by proliferating fibroblasts; these cause nerve root and spinal cord tethering, block CSF flow, and lead to the formation of CSF loculations.
Frequency
United States
The incidence of spinal infections and neoplasms has increased in the United States. In large part, this is due to the increasing number of immunocompromised patients. This population includes chronically debilitated patients (eg, those with diabetes or alcoholism and intravenous drug abusers), transplantation and chemotherapy patients, and those with AIDS.
International
As in the United States, the incidence of spinal infections has increased throughout the world, largely because of the factors mentioned above. (In less than 2 decades, the AIDS epidemic has spread to more than 190 countries in all continents. The World Health Organization estimates that nearly 40 million people had HIV in 2003.1 )
Mortality/Morbidity
Syringomyelia may occur as a complication of arachnoiditis. The exact etiology for syrinx formation is a matter of debate. However, most believe that meningeal adhesions and/or scarring may alter CSF flow. This alteration causes abnormal intraspinal fluid pulse pressure and leads to an increased amount of CSF entering the cord parenchyma and the central canal (depending on its degree of patency), with subsequent syringohydromyelia. A similar mechanism has been proposed to explain syrinx formation in Chiari malformations.
Spinal arachnoid cysts are usually congenital, but they have been reported in association with arachnoiditis, ankylosing spondylitis, and subdural hemorrhages. These cysts are frequently associated with syrinx formation, cord atrophy, or both.
Arachnoiditis ossificans is a rare complication of leptomeningitis. Case reports have confirmed mature bone with osseous marrow, trabeculae, and osteoblast proliferation within the subarachnoid space. Early diagnosis and surgical intervention are necessary if the patient is to have any acceptable degree of recovery.
See also Clinical Details.
Race
No race predilection exists.
Sex
No sex predilection exists.
Age
Years may pass before patients with arachnoiditis become clinically symptomatic. As a result, arachnoiditis is primarily a disorder of adults.
Anatomy
Spinal disease may affect the cord (myelitis), meninges and subarachnoid space (arachnoiditis, leptomeningitis), vertebral bodies and intervertebral disc spaces (discitis, osteomyelitis), or paraspinal soft tissues (epidural abscess, phlegmon).
Presentation
Patients with arachnoiditis may have paresis caused by compression or tethering of the spinal cord and cauda equina or polyradiculopathy caused by compression or involvement of the cauda equina alone. Symptoms include low back pain or radicular pain, leg weakness, gait disorder, and incontinence.Preferred Examination
Because of its noninvasive nature, multiplanar capabilities, and superb soft-tissue characterization, MRI is the study of choice for the diagnostic evaluation of arachnoiditis (see MRI). For patients in whom MRI is contraindicated, CT myelography is an acceptable alternative. Recently gadolinium-enhanced intrathecal MR imaging has been described. Currently, this is not FDA approved.
Limitations of Techniques
See the sections for discussions of imaging findings for specific imaging techniques.
Differential Diagnoses
| Arachnoid Cyst | Sarcoidosis, Thoracic |
| Ependymoma, Spine | Spinal Stenosis |
| Hodgkin Disease, Thoracic | Spondylodiskitis |
| Leptomeningeal Carcinomatosis | Tuberculosis, CNS |
| Meningioma, Spine | |
| Meningitis, Bacterial |
More on Arachnoiditis |
 Overview: Arachnoiditis |
| Imaging: Arachnoiditis |
| Multimedia: Arachnoiditis |
| References |
| Next Page » |
References
Global Summary of the HIV/AIDS Epidemic, December 2003. World Health Organization. Available at http://www.who.int/hiv/pub/epidemiology/imagefile/en/index11.html. Accessed August 22, 2007.
Brammah TB, Jayson MI. Syringomyelia as a complication of spinal arachnoiditis. Spine. Nov 15 1994;19(22):2603-5. [Medline].
Georgy BA, Snow RD, Hesselink JR. MR imaging of spinal nerve roots: techniques, enhancement patterns, and imaging findings. AJR Am J Roentgenol. Jan 1996;166(1):173-9. [Medline].
Gero B, Sze G, Sharif H. MR imaging of intradural inflammatory diseases of the spine. AJNR Am J Neuroradiol. Sep-Oct 1991;12(5):1009-19. [Medline].
Gupta RK, Gupta S, Kumar S. MRI in intraspinal tuberculosis. Neuroradiology. 1994;36(1):39-43. [Medline].
Johnson CE, Sze G. Benign lumbar arachnoiditis: MR imaging with gadopentetate dimeglumine. AJNR Am J Neuroradiol. Jul-Aug 1990;11(4):763-70. [Medline].
Munoz A., Hinojosa J., Esparza J. Cisternography and Ventriculography Gadopentate Dimeglumine-Enhanced MR Imaging in Pediatric Patients: Preliminary Report. AJNR. May 2007;28:889-894.
Sharma A, Goyal M, Mishra NK. MR imaging of tubercular spinal arachnoiditis. AJR Am J Roentgenol. Mar 1997;168(3):807-12. [Medline].
Tali ET, Ercan N, Krumina G, et. al. Intrathecal gadolinium (gadopentate dimeglumine) enhanced magnetic resonance myelography and cisternography: results of a multicenter study. Invest Radiol. March 2002;37(3):152-9.
Whiteman ML. Neuroimaging of central nervous system tuberculosis in HIV-infected patients. Neuroimaging Clin N Am. May 1997;7(2):199-214. [Medline].
Further Reading
Keywords
leptomeningitis, inflammation of the meninges, inflammation of the subarachnoid space, infectious arachnoiditis, neoplastic arachnoiditis
