eMedicine Specialties > Radiology > Brain/Spine

Arachnoiditis: Imaging

Author: Alan Holz, MD, Assistant Professor, Department of Radiology, University of Miami School of Medicine; Consulting Staff, Section of Neuroradiology, Memorial Regional Hospital
Contributor Information and Disclosures

Updated: Sep 28, 2007

Radiography

Findings

The 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 Confidence

With radiographic findings, the degree of confidence is high.

Computed Tomography

Findings

MRI 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 Confidence

With conventional CT, the degree of confidence with findings is low. With CT myelography, the degree of confidence is high.

Magnetic Resonance Imaging

Findings

As 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:

• The most common pattern of enhancement is a smooth, linear layer of enhancement outlining the surface of the cord and nerve roots (see Images 9-10).
• The second most common pattern is a nodular pattern with discrete foci of enhancement seen along the surface of the cord (see Images 12-13) and nerve roots.
• The least-common pattern consists of diffuse intradural enhancement that completely fills the subarachnoid space (see Images 14-15).

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.

MR imaging after the administration of intrathecal gadopentate dimeglumine (Gd-DTPA) has been described as a safe, effective technique to diagnose or exclude the diagnosis of arachnoiditis.  In one report, arachnoiditis could not be excluded on routine postoperative intravenous-enhanced MRI in a patient with progressive paraparesis and sphincter incontinence.  Arachnoiditis was differentiated from postoperative changes with intrathecal-enhanced MRI.  Doses ranging from 0.8 to 2 ml of gadolinium mixed with 3 to 5 ml of the patients' CSF under sterile conditions have been injected into the subarachnoid space.  MR imaging was performed utilizing T1-weighted fat-suppressed sequences in 2-3 orthogonal planes.

Purported advantages of gadolinium-enhanced intrathecal MR imaging include an absence of ionizing radiation, the capability of direct multiplanar imaging, an absence of bony artifact, and high spatial and contrast resolution.  It should be noted that although a cooperative multicenter study of 95 patients failed to demonstrate behavioral changes, neurologic alteration, or seizure activity with intrathecal gadolinium, the administration of intrathecal gadolinium is not approved for use by the FDA and has been used off-label. 

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 Confidence

With MRI findings, the degree of confidence is high.

False Positives/Negatives

Sarcoidosis and spinal anesthesia may cause false results.

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