You are in: eMedicine Specialties > Radiology > BRAIN/SPINE ArachnoiditisArticle Last Updated: Sep 28, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 8
  Author: Alan Holz, MD, Assistant Professor, Department of Radiology, University of Miami School of Medicine; Consulting Staff, Section of Neuroradiology, Memorial Regional Hospital Alan Holz is a member of the following medical societies: American College of Radiology, American Society of Neuroradiology, and Radiological Society of North America Editors: Lucien M Levy, MD, PhD, Director of Neuroradiology, Professor of Radiology, Department of Radiology, George Washington University Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Robert L DeLaPaz, MD, Director, Professor, Department of Radiology, Division of Neuroradiology, Columbia University; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; James G Smirniotopoulos, MD, Professor of Radiology, Neurology, and Biomedical Informatics, Chairman, Department of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences Author and Editor Disclosure Synonyms and related keywords: leptomeningitis, inflammation of the meninges, inflammation of the subarachnoid space, infectious arachnoiditis, neoplastic arachnoiditis INTRODUCTIONSection 2 of 8
  BackgroundArachnoiditis 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. PathophysiologyInfection 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. FrequencyUnited StatesThe 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. InternationalAs 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/MorbiditySyringomyelia 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. RaceNo race predilection exists. SexNo sex predilection exists. AgeYears may pass before patients with arachnoiditis become clinically symptomatic. As a result, arachnoiditis is primarily a disorder of adults. AnatomySpinal 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). Clinical DetailsPatients 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 ExaminationBecause 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 TechniquesSee the sections for discussions of imaging findings for specific imaging techniques. DIFFERENTIALSSection 3 of 8
Arachnoid Cyst Ependymoma, Spine Hodgkin Disease, Thoracic Leptomeningeal Carcinomatosis Meningioma, Spine Meningitis, Bacterial Sarcoidosis, Thoracic Spinal Stenosis Spondylodiskitis Tuberculosis, CNS RADIOGRAPHSection 4 of 8
FindingsThe spinal cord and nerve roots cannot be evaluated with routine plain radiographs. However, myelography with the intrathecal administration of iodinated contrast material is useful in evaluating the contents of the thecal sac. In adults, the conus medullaris normally terminates between the T12-L1 and L1-L2 levels. Below these levels, the nerve roots normally float freely within the thecal sac. Meningeal inflammation leads to thickened or clumped nerve roots, blockage of CSF flow, and the formation of CSF loculations (see Images 1-2). Degree of ConfidenceWith radiographic findings, the degree of confidence is high. CT SCANSection 5 of 8
FindingsMRI is far superior to conventional CT in the evaluation of arachnoiditis because of the poor contrast resolution between the spinal cord and nerve roots and CSF at CT. However, CT myelography is effective in demonstrating the classic imaging findings of arachnoiditis. These include narrowing or blockage of the subarachnoid space, irregular collections of contrast material, thickened or matted nerve roots, and absent filling of nerve root sleeves (see Image 3). Degree of ConfidenceWith conventional CT, the degree of confidence with findings is low. With CT myelography, the degree of confidence is high. MRISection 6 of 8
FindingsAs previously stated, MRI is the study of choice for the diagnostic evaluation of arachnoiditis. T1-weighted MRIs may reveal an indistinct or absent cord outline due to the increase in the signal intensity of the surrounding CSF (see Image 9, Image 12, Image 14). This may be the result of an elevation in CSF protein content, the presence of inflammatory exudate, or the formation of adhesions along the surface of the spinal cord. T2-weighted MRIs may demonstrate CSF loculation and obliteration of the subarachnoid space or irregularly thickened, clumped nerve roots, which occasionally may be misinterpreted as a tethered cord or a thickened filum terminale (see Images 6-7). With more severe arachnoiditis, progression of nerve root clumping and leptomeningeal adhesions may lead to angular defects in the dural sac. Peripheral adherence of the nerve roots to the walls of the thecal sac produces the so-called featureless, or empty, sac (see Image 8). Contrast enhancement is an inconstant finding. When it does occur, enhancement may be the result of a vascular network within the fibrous stroma that develops in the subarachnoid space. Three patterns of enhancement have been described:
No pattern of enhancement has been found to be characteristic of any specific infectious agent or pathologic process. In general, benign arachnoiditis enhances less avidly than does carcinomatous meningitis; however, MRI findings alone cannot be used to differentiate infection from neoplasm. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Degree of ConfidenceWith MRI findings, the degree of confidence is high. False Positives/NegativesSarcoidosis and spinal anesthesia may cause false results. MULTIMEDIASection 7 of 8
REFERENCESSection 8 of 8
Article Last Updated: Sep 28, 2007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
