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Suspecting and Diagnosing Arachnoiditis

A review of the symptoms noted in a group of patients with arachnoiditis presents an analysis of clinical observations of this disease.
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  • intrathecal calcification
  • enhanced nerve roots (see Figure 2)
  • clumping of nerve roots (see Figure 3)
  • adherence of nerve roots to the wall of the dural sac (see Figure 4)
  • abnormal distribution of nerve roots within the dural sac
  • extradural scarring in continuity with a deformed dural sac
  • Intrathecal pseudocysts
  • Abnormal pattern of dye distribution within the dural sac pseudomeningocele (see Figure 5)
  • intradural scarring
  • dural sac deformity or narrowing
  • residual oil-soluble contrast media in the dural sac
  • multiple deposits of contrast media with irregular distribution (see Figure 6)

Extrapolation of Radiological Findings

Using plain films, only the recognition of an intradural calcification or a residual droplet of oil-soluble dyes (pantopaque) can suggest the presence of ARC. The wide acceptance of surface-coil magnetic resonance imaging (MRI) as a non-invasive diagnostic test—without danger of further re-injury—has made it possible to arrive at a more precise diagnosis, especially when thin slices are used. The axial and sagittal views allow the identification of nerve roots and dural sac pathology displaying, in detail, the type of abnormal findings as described by Ross et al,17 Delamarter et al,18 and others.19,20 Limitation of the usefulness of MRI has been encountered in patients with metal devices in the proximity of the spine or near delicate organs such as the eyes or the brain. In these instances, a myelogram followed by a lumbar spinal CAT scan is indicated.21

Figure 2. Axial view of the MRI of the lumbar spine demonstrating “Enhanced (edematous) nerve roots (black arrows). Figure 3. CAT scan of the lumbar spine demonstrating all nerve roots in a single clump (arrow head). Figure 4. Four axial views of an MRI of the lumbar spine showing in the two upper frames, the normal location of the nerve roots in the posterior half of the dural sac, situated at the L3 vertebra. In the two lower frames, clumped and asymmetrically located nerve roots are seen at L4. (small arrow head). Nerve roots are also adhered to the dural sac on the right, lower frame (large arrow head). Figure 5. Pseudomeningocele (P) posterior to the dural (S) sac at the level of L5, after an L5-S1 discectomy. Figure 6. Distribution of multiple small droplets of pantopaque at different level, from L3 to the end of the dural sac at S2. Figure 7. Axial view of an MRI of a normal lumbar spine showing most of the nerve roots symetrically located in the posterior half of the dural sac. Two nerve roots are ascending toward the anterior corners of the sac in their way toward departing through the lateral foramen.

Other radiological findings, such as when the conus medullaris and nerve roots are either deviated or tethered by adhesions or trapped or compressed by intrathecal scar tissue (identified in an MRI or a CAT scan following myelography22,23), suggest that an adhesive arachnoiditic proliferative process is already going on three months after the injurious event. In either of these imaging studies, the absolute confirmation is obtained when the nerve roots are clumped and asymmetrically located in comparing one side to the other. This abnormal distribution is in contrast to their normal appearance of being symmetrically located on both sides with the roots individually identifiable (see Figure 7). Nevertheless, in the first three months after the injurious event, “enhancement," meaning edema of the nerve roots, may be visualized by intravenously administering the contrast media gadopentate dimeglumine to patients.24 In myelography, images of the dural sac appearing as having being “painted with a brush with little paint," blunting of axillary root pouches, dural cuff cysts, pachymeningitis, and abrupt obliteration of the dural sac are all suggestive of ARC.21

Not uncommonly, the type, location and distribution of symptoms in patients suffering from ARC are atypical because they superimpose the signs and symptoms produced by other underlying disease such as recurrent herniated discs, spinal stenosis, spondylolisthesis, facet arthropathy, meningitis etc.25 This confusion makes the precise clinical diagnosis of arachnoiditis and each of the accompanying spinal conditions difficult and requires a meticulous and careful radiological interpretation. 17,18,21 From the author’s experience, a certain pattern of clinical manifestations were found and documented in every patient seen (see Tables 2 to 5). While such symptoms pointed toward the clinical suspicion of ARC, a case was not considered confirmed unless there was also an unquestionable and objective radiological diagnoses.

Myeloscopy

Other authors have claimed that arachnoiditis can be diagnosed by direct visualization with a myeloscope.26,27 This assertion is questionable at best since the field of vision with this device is very limited. At worse, the invasion of the dural sac does not warrant the information obtained since the arachnoid will undoubtedly be perforated and thus initiate a “flair-up" process if ARC is already present. In addition to having poor documentation from the photographed sites, the extent and location (multiple levels) cannot be determined convincingly. The likelihood that the endoscopist would initiate treatment (lysis of adhesions) in lesions that could not be confirmed by others, have cast a doubt of suspicion over this procedure. Moreover, since it has been shown that those adhesions will form again—and the procedure, itself, may stimulate further noxious stimuli that will exacerbate the clinical syndrome—this diagnostic and therapeutic modality is not recommended.

Electrodiagnostic Studies

Attempts to apply electrodiagnostic tests, including EMG, nerve conductions studies, and evoked potentials—commonly used to diagnose peripheral neuromuscular diseases28,29—have not rendered a consistent pattern that could be identified as that of arachnoiditis. Nevertheless, they have been useful in confirming the presence of other concomitant illnesses such as radiculopathy, diabetic neuropathy, etc. or to rule out neurological disease such as multiple sclerosis, amyotrophic lateral sclerosis, and others. Aside from these benefits, a definite electrodiagnostic pattern has not been found that would make any of these tests pathognomonic of arachnoiditis.

Current Epidemiology

As Table 1 shows, most cases of lumbar arachnoiditis represented in this series were most likely caused by therapeutic interventions such as laminectomies,30,31 fusions,32 epidural anesthesia,33 spinal anesthesia,34 epidural injections of steroids,35 neuroplasty or adhesiolysis,36 neurolytic agents,29 some local anesthetics in high concentration,38 epidural blood patches39,40 and, less commonly, other invasive diagnostic procedures such as traumatic myelograms with water-soluble dyes,41 discographies, lumbar punctures, and any other invasion of the vertebral canal. These cases may, in fact, be due not to the procedure itself but most likely to the accidental injury of the dura, with injection of an irritant chemical substance (methylene blue, acrylate, etc), blood into the intrathecal space, or even single traumatic spinal taps.

Last updated on: April 13, 2017
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