Arachnoid web of the spine: a systematic literature review

Considerations for delayed-onset spinal arachnoid web after intracranial subarachnoid hemorrhage

Spinal arachnoid web (AW) is a rare condition causing spinal cord-related issues. Its cause is often idiopathic but can be linked to past trauma or spine surgery. We describe two cases of AWs that developed after subarachnoid hemorrhage (SAH). Case #1 is a 71-year-old male with nonaneurysmal SAH who developed myelopathy 1 year later. Magnetic resonance imaging revealed upper thoracic cord edema and an AW. Case #2 is a 57-year-old female who underwent coiling of a ruptured basilar artery aneurysm and ventriculoperitoneal shunting for hydrocephalus. Twenty months later, she developed mid-thoracic AW requiring surgical resection. Both patients showed symptom improvement postresection avoiding further reoperation. History of SAH is emerging as a risk factor for AW development, emphasizing the importance of monitoring delayed-onset myelopathy and back pain in recent SAH patients.

Arachnoid webs with spinal cord compression: insights from three cases

Spinal arachnoid webs are intradural bands of abnormally formed arachnoid tissue, located within the subarachnoid space and causing compression of the dorsal aspect of the spinal cord. Arachnoid webs are uncommon and can be difficult to treat. We report 3 patients presenting with a spinal arachnoid web within a 6-month period. All of them exhibited signs of thoracic myelopathy and the MRI showed the pathognomonic 'scalpel sign'. Two of the patients underwent surgery for removal of their spinal arachnoid web, whereas the third patient case is currently being managed conservatively. We also present our 2D intraoperative video for arachnoid web removal and spinal cord decompression.

A case of neurosurgical treatment of thoracic dorsal arachnoid web

Background

Dorsal arachnoid webs constitute abnormal formations of arachnoid that tend to occur in the upper thoracic spine and can lead to spinal cord displacement. Patients typically present with back pain, sensory disturbances, and weakness. It may also obstruct the cerebrospinal fluid (CSF) flow, leading to syringomyelia. In magnetic resonance (MR) studies, the "scalpel sign" is a classical finding, and it may also be accompanied by syringomyelia attributed to CSF flow. Definitive surgical resection is the mainstay of treatment.

Case Description

A 31-year-old male presented with mild weakness in the right leg and diffuse lower extremity sensory changes. The MR showed the typical "scalpel sign" at the T7 level consistent with diagnosing a spinal arachnoid web. He underwent a T6-T8 laminotomy for lysis of the web and decompression of the thoracic cord. Postoperatively, his symptoms improved markedly.

Conclusion

Surgical resection is the treatment of choice when an arachnoid web is documented on an MR and correlates with the patient's clinical symptoms/signs.

Long-term outcome of surgical treatment for idiopathic spinal arachnoid web: A case series

OBJECTIVE

Spinal arachnoid web (SAW) is a rare condition of the spine with limited long-term follow-up data in the literature. The longest reported follow-up period was an average 3.2 years. The objective of this study is to report our long-term results of patients who underwent surgical treatment for symptomatic idiopathic SAW.

METHODS

We conducted a retrospective review of cases of idiopathic SAW that were operated between 2005-2020. We collected preoperative and last follow-up (LFU) data on motor force, sensory loss, pain, upper motor neuron (UMN) sign, gait disorder, sphincter dysfunction, syringomyelia, hyperintensity on T2-MRI, appearance of newer symptoms and number of reoperations.

RESULTS

Our study included 9 patients with a mean follow-up period of 3.6years (range 2-9.1years). The surgical intervention involved a standard centered laminectomy, durotomy and arachnoid lysis. At presentation, motor weakness was present in 77.8% of patients, sensory loss in 66.7%, pain in 88.9%, sphincter dysfunction in 33.3%, UMN sign in 22%, gait disorder 55.6%, syringomyelia in 55.6% and MRI T2 hyperintensity in 55.6% of patients. At LFU, there was an improvement in all symptoms and signs to varying degrees. No new neurological symptoms appeared postoperatively, and there was no recurrence during the follow-up period.

CONCLUSION

Our results demonstrate that the reported immediate and short-term favorable outcomes following arachnoid lysis for symptomatic SAW persist over a long-term period and the risk of readhesion-correlated neurological deterioration following conventional surgical intervention is low.

Spinal arachnoid webs in adults: Clinical and imaging features in a multicenter study

BACKGROUND AND PURPOSE

Spinal arachnoid webs (SAWs) are rare and can present with myelopathic symptoms. This study aims to add 85 more cases of SAWs to the literature so we can continue to analyze clinical and imaging trends of SAWs to better understand this entity and its natural history.

METHODS

An institutional review board-approved retrospective review of SAW cases between 2016 and 2022 within a metropolitan, multihospital network was performed, searching for MR and CT reports that included "arachnoid web." Of 108 identified reports, 85 patients had imaging and/or pathologically proven arachnoid webs. Demographic and clinical data were collected. Images were analyzed for SAW level, point of maximum kyphosis, presence of cord expansion, and signal intensity. The electronic medical record (EMR) was reviewed for age, sex, symptom presentation and duration, management, and outcomes.

RESULTS

Of 85 cases, the most common presenting chief complaint was back pain and weakness. All (100%) SAWs were in the dorsal thoracic subarachnoid space, with 87% (74/85) located from thoracic (T) 2 to T6. Spinal cord expansion and signal abnormality were present in 54.1% and 23.5%, respectively. Twenty-six underwent surgical resection with 20 showing improvement of at least one symptom.

CONCLUSION

We present 85 additional cases of SAWs to the existing literature. Our cases all occurred in the dorsal thoracic subarachnoid space, predominantly from T2 to T6. Patients present with symptoms like other causes of cord compression, and spinal MR studies should be evaluated routinely for the findings of SAWs. Further research could focus on understanding SAW prevalence, risk factors, and pathophysiology.

Arachnoid webs causing rostral syrinx due to ball-valve effect: an illustrative report of two cases

An arachnoid web is a pathological formation of the arachnoid membrane. It is a rare phenomenon but is known to lead to syrinx formation in the spinal cord along with pain and neurological deficits. On imaging, the 'scalpel sign' is pathognomonic for an arachnoid web. The etiology of syrinx formation from an arachnoid web is currently unknown. This report documents the only two cases of arachnoid webs with an extensive syrinx in which a likely pathophysiologic mechanism is identified. Both cases presented with motor deficits. The patients had no history of trauma or infection. After extensive workup in both patients and observation of the scalpel sign an arachnoid web was suspected. In both cases, the patients were treated surgically after an arachnoid web was suspected. Intra-operative ultrasound visualized in both cases demonstrates a fenestration in the web that allowed passage of cerebrospinal fluid in a rostral-caudal direction due to a ball-valve effect.

Dorsal arachnoid web: the ‘scalpel’ sign—a case report and differential diagnosis

Background

Arachnoid web of the spine is a not so common lesion of the spinal cord. It is a band-like arachnoid tissue in the intradural extramedullary compartment that extends to the surface of the spinal cord, with a tendency to occur in the upper dorsal spine causing focal dorsal indentation of the cord that has been coined the ‘scalpel sign’. Patients usually present with progressive weakening and numbing of bilateral lower limb.

Case presentation

A 58-year-old man presented with difficulty in walking and weakness of right leg for 1 year, aggravated over the previous 2 months. There was no history of trauma or fever. Magnetic resonance imaging (MRI) of the dorsal spine was done which revealed a small syrinx within the cord at D4 vertebral level on right side. There was sharp dorsal indentation of the spinal cord and widening of the arachnoid space below this level. This appearance was similar to a surgical scalpel. The anterior subarachnoid space was preserved. On post-contrast images, no parenchymal or meningeal enhancement was detected. The patient was taken up for surgery as the symptoms further progressed. Laminectomy was done from D3 to D7 under general anesthesia, with release of arachnoid web and adhesions. Histology of the resected specimen revealed epithelial cells and fibrous tissue. No inflammatory or neoplastic cells were observed.

Conclusions

Thoracic arachnoid web is a rare entity, which if not treated can have devastating effects on a patient’s neurological function. Careful evaluation of radiological findings is important to avoid delay in diagnosis. Surgery is the only curative treatment and is known to have a favorable outcome.

Scalpel sign: Dorsal thoracic arachnoid web, thoracic arachnoid cyst and ventral cord herniation

The “Scalpel sign” is a radiological sign which can be identified on magnetic resonance imaging and indicates dorsal compression of the spinal cord [1]. Prior descriptions of a “Scalpel sign” have been reported in the literature and the awareness and identification of this pathognomonic sign may aid in the rapid diagnosis and treatment of patients with dorsal arachnoid web, dorsal arachnoid cyst or ventral cord herniation. We describe 3 cases which highlight these rare conditions for which this sign is pathognomonic and summarize the pertinent literature related to these disorders [1,2].

Imaging of intraspinal cystic lesions: A review

Several distinct conditions present as cystic or pseudocystic lesions within the spinal canal. Some of the most common spinal cystic lesions include spinal meningeal cysts, juxtafacet cysts, dermoid/epidermoid cysts, nerve sheath tumors, and syringohydromyelia. Clinical presentation is usually nonspecific and imaging characteristics are frequently overlapping, which may pose a challenging presurgical diagnosis. We provide a pictorial review of cystic intraspinal lesions and discuss the main imaging features that can aid the neuroradiologist in the differential diagnosis. First, we propose a categorization of the lesions according to their location as extradural, intradural extramedullary, and intramedullary. This is a crucial initial step in the diagnostic workup and surgical planning. Second, for each of these locations, we organize the lesions according to their etiology: congenital and developmental disorders, degenerative disorders, traumatic or postsurgical collections, infectious conditions, neoplastic lesions, and other miscellaneous disorders. Finally, we summarize the clinical highlights and MR features that provide important insights for the differential diagnosis. MR is the technique of choice in presurgical evaluation and postsurgery follow-up. It provides accurate lesion localization and characterization and, most of the times, it will allow a confident differential diagnosis. High-resolution three-dimensional T2-weighted sequences and diffusion-weighted imaging can provide important hints in specific cases. Signal correlation with T1-weighted and fat-saturated sequences allows to differentiate true cystic lesions from hemorrhage or fat tissue.

Cine MRI Is Useful for the Diagnosis of Intradural Arachnoid Cyst with Spinal Arachnoid Web: A Case Report

CASE

A 28-year-old woman developed gait disturbance due to lower limb weakness 3 years before presentation. Conventional magnetic resonance imaging (MRI) findings were inconclusive; therefore, we performed cine MRI, which confirmed the presence of a pulsatile cyst on the posterior thoracic spinal cord. The cyst compressed the spinal cord, and its pulsations synchronized with the patient's heartbeats. We resected the intradural arachnoid cyst and thickened arachnoid membrane. The gait disturbance improved after surgery.

CONCLUSIONS

Cine MRI can be used to identify a pulsating arachnoid cyst that cannot be visualized with a conventional MRI. Cine MRI is useful in patients with unexplained spinal symptoms.

Thoracic spinal arachnoid web and syringomyelia with rostral expansion to the first cervical spinal cord level: Case report

INTRODUCTION AND IMPORTANCE

A spinal arachnoid web is a rare pathology that has been associated with the development of syringomyelia. Syrinx expansion can occur, which can result in the development of new symptoms. In the current literature, the farthest rostral expansion of the associated syrinx has been to the C3 spinal level.

CASE PRESENTATION

We present a 49-year-old Hispanic male with a thoracic spinal arachnoid web and an associated syrinx spanning from C1 to T7 spinal level. The patient developed upper extremities radicular symptoms that worsened over time. He underwent surgical management with T6-8 laminectomy and excision of the web. Postoperative follow-up evaluations demonstrated progressive clinical improvement with eventual resolution of symptoms and syringomyelia.

CLINICAL DISCUSSION

Syringomyelia secondary to a thoracic spinal arachnoid web is a progressive disease that can expand rostrally to the C1 spinal level. The clinical presentation usually involves the lower extremities. However, if the upper thoracic or cervical spinal cord is involved, patients can also present symptoms in the upper extremities. Management usually involves surgical excision of the web in order to decompress the subarachnoid space and restore the normal cerebrospinal fluid (CSF) flow.

CONCLUSION

Our case suggests that syringomyelia secondary to a spinal arachnoid web may continuously expand with concomitant worsening of symptoms. However, surgical resection is curative with possible remission of symptoms and normalization of spinal anatomy.

Pulsating Spinal Arachnoid Cyst as a Hidden Aggravating Factor for Thoracic Spondylotic Myelopathy: A Report of 3 Cases

CASE

We report 3 cases of thoracic myelopathy caused by vertebral osteophytes and coexisting intradural spinal arachnoid cyst (SAC), which was difficult to diagnose on preoperative magnetic resonance imaging. Intraoperative ultrasound sonography revealed spinal cord impingement because of osteophytes and a pulsating intradural SAC. Repeated pincer compression on the spinal cord seemed to be associated with their paraparetic symptoms.

CONCLUSION

In treating patients presenting with unexplained progressive myelopathy with small ossified lesion in the thoracic spine, close attention should be paid to a coexisting SAC as a hidden aggravating factor for thoracic myelopathy.

Atypical radiographic case of arachnoid web without scalpel sign

Background:

Spinal arachnoid webs (SAW) occur when abnormally thickened bands of arachnoid membranes commonly located dorsal to the thoracic spine cause blockage of normal cerebrospinal fluid (CSF) flow, resulting in focal cord compression and myelopathy. The pathognomonic MR finding for SAW is the “positive scalpel sign” comprised of an enlarged dorsal CSF space with a normal ventral subarachnoid space. The main differential diagnostic consideration for SAW is idiopathic spinal cord herniation (ISCH); however, for ISCH, MR studies classically demonstrate ventral displacement of the spinal cord through an anterior dural defect. Here, we describe a 60-year-old female with an atypical SAW at the T3-T4 level (i.e., the preoperative MR failed to demonstrate the “positive scalpel sign”). Nevertheless, at surgery, intraoperative ultrasonography confirmed that SAW was present and was decompressed/marsupialized/removed.

Case Description:

A 60-year-old female presented with sensory impairment to both lower extremities. The thoracic MR images showed an enlarged dorsal CSF space at the T3-T4 level but without the “scalpel sign” suggesting “interruption” of CSF flow by thickened bands of focal dorsal arachnoidal tissues. Although the initial preoperative diagnosis was ISCH, intraoperative ultrasound (IOUS) confirmed the presence of a thickened arachnoid band, confirming the diagnosis of a SAW that was appropriately decompressed/resected.

Conclusion:

Correctly, establishing the preoperative diagnosis of a SAW based on MR imaging may sometimes be difficult as the typical “scalpel sign” may not be present in all patients. Notably, in cases like this one, IOUS may critically confirm the diagnosis of SAW thus leading to appropriate SAW decompression/removal.

Correlation of Spinal Cord Injury With Development Of Spinal Arachnoid Cysts: Two Case Reports

Background

Spinal arachnoid cysts are rare entities, which are composed of a duplication in the arachnoid membrane and resultant cerebrospinal fluid collection, which may present with a progressive myelopathy. The most common symptoms caused by spinal cord compression are paraesthesia, neuropathic pain, paresis and gait ataxia.

Clinical cases

We report here 2 cases from different perspectives of a spinal arachnoid cysts in spinal cord injury. The first case was the occurrence of a spinal cord injury due to compression of a spinal arachnoid cysts causing myelopathy. The second case is a patient who had a traumatic paraplegia for which stabilizing surgery was required and who subsequently developed a spinal arachnoid cysts with neuropathic pain. Both cases required surgery with immediate improvement. However, after a few months both patients needed a revision due to recurrence.

Conclusion

Spinal arachnoid cysts may present with a heterogeneous clinical picture. If cysts are not clinically apparent, a conservative treatment with careful observation can be a justifiable option. In patients with progressive symptoms, surgery is the gold standard of care. However, the literature describes the need for revision surgery in only 12.5% of cases. Regular follow-up is necessary because both of the patients reported here needed revision surgery.

Pathophysiology and surgical treatment of spinal adhesive arachnoid pathology: patient series

BACKGROUND

Spinal adhesive arachnoid pathology is a rare cause of myelopathy. Because of rarity and variability, mechanisms of myelopathy are unknown. The authors retrospectively analyzed patients to understand pathophysiology and provide implications for surgical treatment.

OBSERVATIONS

Nineteen consecutive patients were studied. Thirteen patients had a secondary pathology due to etiological disorders such as spinal surgery or hemorrhagic events. They received arachnoid lysis (4 patients), syringo-subarachnoid (S-S) shunt (8 patients) with or without lysis, or anterior decompression. Three of them developed motor deterioration after lysis, and 6 patients needed further 8 surgeries. Another 6 patients had idiopathic pathology showing dorsal arachnoid cyst formation at the thoracic level that was surgically resected. With mean follow-up of 44.3 months, only 4 patients with the secondary pathology showed improved neurological grade, whereas all patients with idiopathic pathology showed improvement.

LESSONS

The idiopathic pathology was the localized dorsal arachnoid adhesion that responded to surgical treatment. The secondary pathology produced disturbed venous circulation of the spinal cord by extensive adhesions. Lysis of the thickened fibrous membrane with preservation of thin arachnoid over the spinal veins may provide safe decompression. S-S shunt was effective if the syrinx extended to the level of normal subarachnoid space.

Spinal Arachnoid Webs: Presentation, Natural History, and Outcomes in 38 Patients

BACKGROUND

Spinal arachnoid webs are rarely described bands of thickened arachnoid tissue in the dorsal thoracic spine. Much is unknown regarding their origins, risk factors, natural history, and outcomes.

OBJECTIVE

To present the single largest case series, detailing presenting symptoms and outcomes amongst operative and nonoperative patients, to better understand the role of intervention.

METHODS

This retrospective chart review identified 38 patients with arachnoid webs. Patient demographics, radiologic signs, symptoms, and surgical history data were extracted from the electronic medical record. Symptoms were divided by location and character. 28 patients were successfully contacted for follow up outcome surveys.

RESULTS

26 patients (68%) underwent surgical intervention, 12 (32%) were managed non-operatively. 15 (39%) patients had undergone a previous unsuccessful surgery at a different site for their symptoms prior to arachnoid web diagnosis. Commonly presenting symptoms included myelopathy (68%), focal thoracic back pain (68%), lower extremity weakness (45%), numbness and sensory changes (58%), and lower extremity radicular pain (42%), upper extremity weakness (24%), and radicular pain (37%). Focal thoracic pain was associated with thoracic level (P < .02). Myelopathic symptoms were less common in postoperative patients. Postoperative patients described significantly more upper extremity (P < .01) and thoracic (P < .01) numbness and paresthesias. Surveyed nonoperative patients universally described their symptoms as either stable or worsening.

CONCLUSION

Spinal arachnoid webs present with thoracic myelopathy and back pain but can also present with upper extremity symptoms. Surgical intervention stabilizes or improves symptoms and is well received. Nonoperative patients do not spontaneously improve.

Spinal Arachnoid Web: A didactic report of two cases with clinical, radiological, surgical and pathological correlations

BACKGROUND

Arachnoid web (AW) is a rare but probably underestimated cause of spinal cord injury that is complex to diagnose due to subtle MRI findings and similarities to other better-known diseases such as arachnoid cyst (AC) or transdural spinal cord herniation (TSCH). Increased recognition of AW is mandatory since delay in diagnosis can lead to potentially serious neurological sequelae.

CASE PRESENTATIONS

We report two additional cases of AW for didactic purposes, with special emphasis on the distinctive MRI and intraoperative findings. Both patients presented with progressively worsening neurological symptoms, including proprioceptive ataxia, motor weakness, numbness and neuropathic pain. The diagnosis of AW was suspected on the basis of specific MRI criteria, especially the so-called "scalpel sign". Formal confirmation of the diagnosis was obtained in two patients that were managed surgically. Postoperative follow-up demonstrated significant functional recovery.

DISCUSSION

There is a need for better recognition of AW by the medical community. Careful analysis of MRI semiology is crucial for the distinction between AW, AC and TSCH. Prompt and accurate diagnosis is mandatory to conserve functional prognosis, since appropriate surgical treatment with AW resection is curative, halting or even resolving the neurological symptoms.

Thoracic dorsal arachnoid web with rapid onset of symptoms: A report of two cases and brief review of the literature

Background:

Thoracic arachnoid webs are a rare entity and can be challenging to diagnose with sometimes subtle radiographic findings. Arachnoid webs can cause severe cord compression with associated syrinx and resulting myelopathy, weakness, sensory loss, and bowel/bladder dysfunction. There have been a little over 60 cases total reported in the literature with only one systematic review. The cases presented here have unique features including rapid onset of symptoms, symptomatic syrinx extending into the cervical spine, and intraoperative syrinx drainage, all of which are quite rare in the current published literature for arachnoid webs.

Case Description:

Here, we present two patients, a 73-year-old man and 58-year-old man presenting with different symptoms and timing of symptom progression but both with “scalpel sign” and associated syrinx present on their MRIs. Each patient underwent a laminectomy with resection of arachnoid web with complete resolution of symptoms in the first case and significant improvement in the second case. Postoperative imaging in both cases showed almost complete resolution of the syrinx.

Conclusion:

Early clinical evaluation and workup followed by early surgical treatment can lead to dramatic improvement in outcomes after surgery. For patients that are symptomatic from an associated syrinx, a midline myelotomy to facilitate drainage can be considered to be done concomitantly with the arachnoid web resection.

Decompression of a Dorsal Arachnoid Web of the Spine: 2-Dimensional Operative Video

Arachnoid webs of the spine are a relatively rare entity with unique radiological findings, most notably the scalpel-sign on sagittal magnetic resonance imaging (MRI).1-4 To date there have been no videographic descriptions of the surgical treatment for this clinical entity. We present the case of a patient with progressive myelopathy and MRI showing a cervical and thoracic syrinx with a sharp transition point at the level of the T5 vertebral body. On computed tomography myelogram, there was preserved cerebrospinal fluid (CSF) in the ventral subarachnoid space-this space is often interrupted in ventral cord herniation, and preserved in dorsal arachnoid webs.5 A laminectomy with intradural excision of arachnoid web was offered and the patient consented for the procedure. Preoperatively, a fiducial screw was placed at T5. A T4-6 laminectomy was performed. A clearly compressive arachnoid web was encountered on exposure. Bands were dissected under an operating microscope, restoring normal CSF flow. Ventral dural defect was ruled out by passing a delicot beneath the cord and withdrawing it on the contralateral side. The patient did well and has shown improvement in myelopathic symptoms at 1- and 3-mo follow-up. Arachnoid webs of the spine can be treated effectively with a prudent, stepwise approach, and careful microsurgical technique. The neurosurgeon should consult closely with their neuroradiology colleagues to rule out other entities prior to the operation, such as ventral cord herniations, which can mimic dorsal arachnoid webs radiologically and clinically. We have received informed consent of the patient to submit this video.

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

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.

Arachnoid Web Fenestration: Diagnostic and Surgical Nuances

Arachnoid web (AW) is a rare phenomenon that has only been described in small case reports and case series,¹ most commonly presenting with upper motor neuron signs and subtle radiographic findings, such as the classically described "scalpel sign."² In this report, we demonstrate the use of imaging and operative techniques that have not been previously shown in the literature as a video for AW. These include high-definition magnetic resonance imaging (MRI) sequences for preoperative diagnosis, use of intraoperative ultrasonography for identification of adhesions, and operative technique for AW fenestration (Video 1). The patient consented to this manuscript. A 64-year-old female patient developed progressive difficulty with balance and ambulation that particularly worsened over the last 4 months associated with tingling and numbness in the bilateral lower extremities. Physical examination revealed spastic gait and upper motor neuron signs in the lower extremities along with left foot drop. MRI revealed a chronic noncontrast-enhancing intramedullary lesion, along with a spinal cord indentation at the level T6 with an associated fiber between the cord and the posterior dura. Surgical intervention was performed with the use of intraoperative fluoroscopy and ultrasound for real-time identification of the surgical site and the AW. Under the microscope, the dura was incised while preserving the arachnoid. The AW was carefully dissected, leaving the portions that were tethered onto the cord. Two weeks postoperatively, the patient's gait was markedly improved, with resolved neurologic function in the lower extremities. Follow-up MRI at 3 months demonstrated resolved medullary syrinx and normalization of the spinal cord contour.

Multi-modality imaging evaluation of the dorsal arachnoid web

PURPOSE

Dorsal arachnoid web (DAW) is a rare intradural abnormality which is associated with progressive myelopathy. Our objective was to review multi-modality imaging techniques demonstrating the scalpel sign appearance in evaluation of DAW.

METHODS

We retrospectively reviewed various imaging modalities of patients found to have DAW at our institution during January 2015 to February 2020. Five patients underwent surgical decompression with pathological correlation. The remaining patients were presumptively diagnosed based on the characteristic finding of scalpel sign. Clinical data were evaluated and correlated to imaging findings. All imaging modalities demonstrated the characteristic scalpel sign.

RESULTS

Sixteen patients (10 females, and six males) with multi-imaging modalities were evaluated. Their mean age was 52 year (range 23-74 years). Fifteen patients underwent conventional spine MRI. Further high-resolution MR imaging techniques, e.g. 3D T2 myelographic sequence, were utilized with two patients. MRI spine CSF flow study was performed to evaluate the flow dynamic across the arachnoid web in one patient. Eight patients were evaluated with CT myelogram. Syrinx formation was discovered in seven (44%) patients; five (71%) of them underwent surgical resection and decompression. Two patients underwent successful catheter-directed fenestration of the web with clinical improvement. We found a statically significant positive correlation between the degree of cord displacement and compression with syrinx formation (r = 0.55 and 0.65 with p-value of 0.03 and 0.009, respectively).

CONCLUSION

DAW has characteristic scalpel sign independent of imaging modality. Multi-modality imaging evaluation of DAW is helpful for evaluation and surgical planning.

Diagnosis and Surgical Treatment of Thoracic Dorsal Arachnoid Web: A Report of Two Cases

Introduction

An arachnoid web (AW) is a relatively rare disease and shows clinical symptoms and radiological findings similar to those of an arachnoid cyst (AC) or spinal cord herniation (SCH). Since the operative procedures for an AW are generally different from those intrathecal disorders, correct preoperative differential diagnosis is important. The purposes of this study were to report the usefulness of magnetic resonance imaging (MRI) and computed tomography (CT) myelography for diagnosing AW and to show the histological findings and clinical results. Case Description. Two patients, a 79-year-old man and a 43-year-old woman, are presented. The primary diagnoses were AC with ossification of the ligamentum flavum and epidural hematoma, respectively, in previous hospitals. They were finally diagnosed by the characteristic MRI and CT myelogram finding called the “scalpel sign.” Histological findings showed epithelial cells and fibrous tissue derived from arachnoid tissues and microcalcifications. After surgery, the scalpel sign has vanished, and aggravation of their symptoms was prevented.

Conclusion

An AW is refractory, but early detection by MRI and CT myelography and early treatment improve outcomes after surgery.

Surgical Release of a Dorsal Thoracic Arachnoid Web

Dorsal arachnoid web (DAW) is a rare clinical entity with unknown etiology, and it can mimic other conditions on imaging.^1,2 We present a surgical video of a patient with DAW that was misdiagnosed as ventral cord herniation. A 35-year-old woman presented with upper back pain and progressive bilateral lower extremity weakness and numbness for a few months. Magnetic resonance imaging (MRI) of the thoracic spine (T) showed ventral cord displacement with a syrinx that extended from T2-4. The computed tomography myelogram showed no contrast anterior to the spinal cord. The patient underwent T3-5 laminectomy. Intraoperatively, we found a thoracic DAW and cord displacement with no herniation (Video 1). We performed adhesiolysis to restore the cerebrospinal fluid circulation. On 4-month follow-up, the patient examination had demonstrated progressive improvement of her previous symptoms (weakness, numbness, and urinary retention), and the repeat MRI scan showed a significant reduction in the size of the syrinx. DAW can mimic other pathologies on preoperative imaging, such as ventral cord herniation and arachnoid cyst. The presence of "scalpel sign" and a syrinx on MRI with no arachnoid cyst on myelography support the diagnosis of DAW.

Percutaneous Fenestration of a Spinal Arachnoid Web Using an Intrathecal Catheter: Effect on Cerebrospinal Fluid Flow and Clinical Status

Background

Spinal arachnoid webs are a rare anatomic entity manifesting as neuropathic back pain, compressive myelopathy, radiculopathy, and hydrocephalus. Typical treatments include hemilaminectomy or full laminectomy with durotomy and microsurgical resection, which can result in secondary scarring and recurrent blockage of cerebrospinal fluid (CSF) flow perpetuating the cycle.

Case Description

A 66-year-old woman presented with progressively worsening gait and memory. Magnetic resonance imaging demonstrated an arachnoid web in the high thoracic region, causing CSF flow obstruction and hydrocephalus. A standard lumbar drainage catheter was introduced percutaneously into the lumbar thecal sac and advanced in a cephalad direction, across the arachnoid web, to the high thoracic region. The patient underwent continuous CSF drainage through this catheter for a total of 3 days, displaying measurable clinical improvement that persisted at the 3-month follow-up visit. Phase-contrast magnetic resonance imaging demonstrated interval reconstitution of dorsal synchronous CSF flow at the second thoracic vertebral level, both on day 3 and at the 3-month control imaging study.

Conclusions

This minimally invasive approach seems useful in achieving restoration of spinal fluid flow at the thoracic region when the underlying blockage results from an arachnoid web and leads to quantifiable clinical improvement.

Rare dorsal thoracic arachnoid web mimics spinal cord herniation on imaging

Background:

Dorsal arachnoid webs (DAWs) are rare clinical entities that can mimic other conditions on magnetic resonance imaging (MRI). Here, we present a case of DAW that was misdiagnosed on MR as a ventral cord herniation.

Case Description:

A 35-year-old female presented with a 1-year history of lower extremity weakness and numbness. The MRI of the thoracic spine showed ventral cord displacement with syringomyelia. The computed tomography myelogram demonstrated ventral cord herniation. Intraoperatively, the patient had a dorsal thoracic web in the absence of cord herniation. Within 8 postoperative weeks, the patient had improved, and the follow-up MI showed a significant reduction in the syrinx size.

Conclusion:

On MR scans, DAWs may look like ventral cord herniation. However, the positive “scalpel sign” and syrinx, the absence of an arachnoid cyst on myelography, and the findings on cine MR help differentiate DAWs from ventral cord herniation.