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      Neuroimaging findings and pathophysiology of dorsal spinal arachnoid webs: illustrative case

      case-report

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          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          BACKGROUND

          Spinal arachnoid webs are uncommon and difficult to diagnose, especially because causative intradural transverse bands of arachnoid tissue are radiographically occult. Left untreated, arachnoid webs may cause progressive, debilitating, and permanent neurological dysfunction. Conversely, more than 90% of patients may experience rapid neurological recovery after resection, even with a prolonged duration of presenting symptoms. Indirect imaging signs such as spinal cord indentation and compression with cerebrospinal fluid (CSF) flow alteration provide crucial diagnostic clues that are critical in guiding appropriate management of such patients.

          OBSERVATIONS

          The authors reported a patient with no significant medical history who presented with back pain, progressive lower extremity weakness, gait ataxia, and bowel and bladder incontinence. They discussed multimodality imaging for determining the presence of arachnoid webs, including magnetic resonance imaging, phase-contrast CSF flow study, computed tomography myelography, and intraoperative ultrasound. They also discussed the detailed anatomy of the spinal subarachnoid space and a plausible pathophysiological mechanism for dorsal arachnoid webs.

          LESSONS

          The authors report on a patient who underwent comprehensive imaging evaluation detailing the arachnoid web and whose subsequent anatomical localization and surgical treatment resulted in a full neurological recovery.

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          Most cited references44

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          Unraveling the riddle of syringomyelia.

          Dan Greitz (2006)
          The pathophysiology of syringomyelia development is not fully understood. Current prevailing theories suggest that increased pulse pressure in the subarachnoid space forces cerebrospinal fluid (CSF) through the spinal cord into the syrinx. It is generally accepted that the syrinx consists of CSF. The here-proposed intramedullary pulse pressure theory instead suggests that syringomyelia is caused by increased pulse pressure in the spinal cord and that the syrinx consists of extracellular fluid. A new principle is introduced implying that the distending force in the production of syringomyelia is a relative increase in pulse pressure in the spinal cord compared to that in the nearby subarachnoid space. The formation of a syrinx then occurs by the accumulation of extracellular fluid in the distended cord. A previously unrecognized mechanism for syrinx formation, the Bernoulli theorem, is also described. The Bernoulli theorem or the Venturi effect states that the regional increase in fluid velocity in a narrowed flow channel decreases fluid pressure. In Chiari I malformations, the systolic CSF pulse pressure and downward motion of the cerebellar tonsils are significantly increased. This leads to increased spinal CSF velocities and, as a consequence of the Bernoulli theorem, decreased fluid pressure in narrow regions of the spinal CSF pathways. The resulting relatively low CSF pressure in the narrowed CSF pathway causes a suction effect on the spinal cord that distends the cord during each systole. Syringomyelia develops by the accumulation of extracellular fluid in the distended cord. In posttraumatic syringomyelia, the downwards directed systolic CSF pulse pressure is transmitted and reflected into the spinal cord below and above the traumatic subarachnoid blockage, respectively. The ensuing increase in intramedullary pulse pressure distends the spinal cord and causes syringomyelia on both sides of the blockage. The here-proposed concept has the potential to unravel the riddle of syringomyelia and affords explanations to previously unanswered clinical and theoretical problems with syringomyelia. It also explains why syringomyelia associated with Chiari I malformations may develop in any part of the spinal cord including the medullary conus. Syringomyelia thus preferentially develops where the systolic CSF flow causes a suction effect on the spinal cord, i.e., at or immediately caudal to physiological or pathological encroachments of the spinal subarachnoid space.
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            Dorsal thoracic arachnoid web and the "scalpel sign": a distinct clinical-radiologic entity.

            M.A. Reardon, P Raghavan, K Carpenter-Bailey … (2013)
            Arachnoid webs are intradural extramedullary bands of arachnoid tissue that can extend to the pial surface of the spinal cord, causing a focal dorsal indentation of the cord. These webs tend to occur in the upper thoracic spine and may produce a characteristic deformity of the cord that we term the "scalpel sign." We describe 14 patients whose imaging studies demonstrated the scalpel sign. Ten of 13 patients who underwent MR imaging demonstrated T2WI cord signal-intensity changes, and 7 of these patients also demonstrated syringomyelia adjacent to the level of indentation. Seven patients underwent surgery, with 5 demonstrating an arachnoid web as the cause of the dorsal indentation demonstrated on preoperative imaging. Although the webs themselves are rarely demonstrated on imaging, we propose that the scalpel sign is a reliable indicator of their presence and should prompt consideration of surgical lysis, which is potentially curative.
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              The fine anatomy of the human spinal meninges. A light and scanning electron microscopy study.

              R Weller, D. Nicholas (1988)
              The fine anatomy of the human spinal meninges was examined in five postmortem spinal cords taken within 12 hours after death from patients aged 15 months to 46 years. Specimens of spinal cord were viewed in transverse section and from the dorsal and ventral aspects by scanning electron microscopy. Transverse sections of spinal cord and meninges were also examined by light microscopy. The arachnoid mater was seen to be closely applied to the inner aspect of the dura. An intermediate fenestrated leptomeningeal layer was observed attached to the inner aspect of the arachnoid mater and was reflected ventrally to form a series of dorsal septa. As it arborized laterally over the surface of the cord to surround nerves and blood vessels, the intermediate layer became highly fenestrated but remained distinct from the pia and arachnoid mater. The pia mater appeared to form a continuous layer which was reflected off the surface of the cord to coat blood vessels within the subarachnoid space in a manner similar to that described in the leptomeninges over the human cerebral cortex. Each dentate ligament consisted of a collagenous core which was continuous with the subpial connective tissue and was attached at intervals to the dura; pia-arachnoid cells coated the surface of the dentate ligaments. The present study suggests that the fine anatomy of the human spinal meninges differs significantly from that described in other mammals.
              Article 0 comments Cited 24 times – based on 0 reviews     Review now
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                Author and article information

                Journal
                Journal ID (nlm-ta): J Neurosurg Case Lessons
                Journal ID (iso-abbrev): J Neurosurg Case Lessons
                Journal ID (publisher-id): J Neurosurg Case Lessons
                Title: Journal of Neurosurgery: Case Lessons
                Publisher: American Association of Neurological Surgeons
                ISSN (Electronic): 2694-1902
                Publication date Collection: 17 May 2021
                Publication date (Electronic): 17 May 2021
                Volume: 1
                Issue: 20
                Electronic Location Identifier: CASE2142
                Affiliations
                [1 ]Department of Radiology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, California; and
                Departments of [2 ]Neurosurgery and
                [3 ]Radiology, University of California, Davis, School of Medicine, Sacramento, California
                Author notes
                Correspondence Nancy Pham: University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA. pham.nancy@ 123456gmail.com .

                INCLUDE WHEN CITING Published May 17, 2021; DOI: 10.3171/CASE2142.

                Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

                Article
                Publisher ID: 103171/CASE2142
                DOI: 10.3171/CASE2142
                PMC ID: 9245846
                PubMed ID: 35855021
                SO-VID: 33ffb207-cbd3-4353-be5d-b7b2ab14f559
                Copyright © © 2021 The authors
                License:

                CC BY-NC-ND 4.0 ( http://creativecommons.org/licenses/by-nc-nd/4.0/).

                History
                Date received : 20 January 2021
                Date accepted : 28 February 2021
                Page count
                Figures: 5, Tables: 0, References: 44, Pages: 4
                Categories
                Compound subject: Congenital, Congenital
                Subject: Case Lesson

                Keywords: arachnoid web,mri,ct myelogram,ultrasound,surgery,csf = cerebrospinal fluid,ct = computed tomography,mri = magnetic resonance imaging
                Data availability:
                Keywords: arachnoid web, mri, ct myelogram, ultrasound, surgery, csf = cerebrospinal fluid, ct = computed tomography, mri = magnetic resonance imaging

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