Abstract
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Objective
Idiopathic syringomyelia (IS) associated with occult arachnoid pathology is a relatively rare condition characterized by a subtle onset, atypical clinical manifestations, and significant diagnostic and therapeutic challenges. This study aims to evaluate the radiographic and clinicopathological features of IS to improve surgical management and patient outcomes.
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Methods
In this study, clinical and radiologic data were retrospectively extracted from a single-center syringomyelia database (N=1,039) spanning December 2020 to March 2025. Among these, 15 patients diagnosed with IS underwent preoperative magnetic resonance imaging and myelography to identify the responsible spinal segments precisely. Comprehensive perioperative assessments and clinical outcomes were collected. During surgery, the subarachnoid space (SAS) was thoroughly explored, with complete removal of thickened and adherent arachnoid tissue to restore normal cerebrospinal fluid (CSF) circulation. Additionally, clinical data, pathological features, and surgical outcomes of IS were compared to those of posttraumatic delayed syringomyelia (PTDS) to evaluate potential differences.
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Results
In this series, all patients underwent preoperative myelography, revealing varying degrees of SAS obstruction. For IS cases that received precise and comprehensive arachnoid lysis, overall postoperative outcomes were favorable. Intraoperative pathology confirmed that all IS cases were characterized by noninfectious, nonacute inflammation. The preoperative maximal syrinx/cord ratio averaged 0.70±0.07 (range, 0.54–0.88), while the syrinx resolution rate varied from 12.2% to 100%, with a mean improvement of 29.6%. Patients with PTDS exhibited a relatively higher incidence of hypesthesia and a greater syrinx tension index. However, no significant differences were observed between IS and PTDS in terms of syrinx length, deviation, or location. Notably, the IS group demonstrated significantly better postoperative syrinx resolution and improvement in syringomyelia-related symptoms compared to the PTDS group.
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Conclusion
While both IS and PTDS share a common underlying mechanism of arachnoid adhesions, they differ significantly in pathological features, treatment approaches, and clinical outcomes. In cases of IS, thorough spinal arachnoid lysis at the affected segment could restore normal spinal cord pulsation and CSF circulation, leading to effective syrinx resolution and a favorable long-term prognosis.
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Keywords: Syringomyelia, Arachnoid webs, Myelography, Spinal cord compliance, Arachnoid lysis, Prognosis
INTRODUCTION
Syringomyelia is a neurological disorder characterized by the presence of a fluid-filled cavity within the spinal cord, containing fluid similar to cerebrospinal fluid (CSF) [
1]. It is commonly associated with conditions such as Chiari malformation, spinal cord trauma, tumors, and posthemorrhagic or postinfectious arachnoiditis [
2]. In contrast, idiopathic syringomyelia (IS) is a form of syringomyelia without these identifiable underlying causes, making its diagnosis and treatment particularly challenging [
3,
4]. The prevalence of syringomyelia varies significantly by region, with rates of approximately 8.2 per 100,000 in Western populations [
5], compared to just 1.94 per 100,000 in East Asian populations, as reported in a nationwide epidemiological survey [
6]. Despite its rarity, there is currently a lack of single-center clinical case series specifically focused on the diagnosis and treatment of IS, underscoring the need for further clinical investigation.
Arachnoid webs are intradural, extramedullary transverse bands that typically cause localized compression on the dorsal surface of the spinal cord, with a particular predilection for the upper spinal cord. IS with occult arachnoid webs (IS-OAW) refers to the development of fluid-filled syrinx within the spinal cord without an identified cause. The presence of subtle or undetectable arachnoid webs within the subarachnoid space (SAS) could disrupt normal CSF flow, alter spinal cord pressure dynamics, and potentially contribute to syrinx formation.
In some cases, IS-OAW may be discovered incidentally or remain asymptomatic, identified only through routine screening or incidental imaging findings. The exact etiology of these webs is often unclear, as they tend to be relatively occult. When symptomatic, patients might present with a wide range of neurological signs, including pain, sensory disturbances, spasticity, paralysis, and abnormal reflexes. Other potential symptoms include toe walking, constipation, and incontinence, which often prompt further evaluation with magnetic resonance imaging (MRI) [
7]. For these patients, addressing the underlying structural causes of the syrinx, such as arachnoid adhesions, offers the best chance for lasting neurological improvement [
7]. In particular, noninfectious and nontraumatic arachnoid adhesions, including occult webs or scarring within the spinal SAS, should be managed through intradural exploration and decompression to restore normal CSF circulation, a critical step in preventing syrinx progression [
4].
However, the precise mechanisms driving CSF obstruction in cases of primary arachnoid webs remain poorly understood. In this study, we retrospectively analyzed a consecutive series of patients with IS from a single-center syringomyelia database, comparing them with cases of posttraumatic delayed syringomyelia (PTDS). By examining their clinical presentations, imaging findings, pathological features, and surgical outcomes, this study aims to provide valuable clinical insights into the diagnosis and management of IS-OAW, ultimately improving patient prognosis.
MATERIALS AND METHODS
1. Patient Selection
From December 2020 to March 2025, a retrospective analysis was conducted on a consecutive series of syringomyelia patients from a single-center database, which included 1,039 cases. Following a detailed screening process, 15 patients diagnosed with IS-OAW who underwent surgical treatment met the inclusion criteria for this study (
Fig. 1).
This study was conducted by the principles of the Declaration of Helsinki. Ethical approval (No. 2018027001) for this study was provided by the Ethical Committee Xuanwu Hospital Capital Medical University, Beijing, China.
Inclusion criteria: (1) The patients with MRI demonstrating syringomyelia; (2) The patients who underwent surgery (posterior laminectomy and spinal arachnoid lysis) in our center.
Exclusion criteria: (1) Patients with identifiable etiologies, including Chiari malformation type I, spinal trauma, tumors, or infectious adhesive arachnoiditis; (2) patients with a history of spinal fusion or instrumentation surgery; (3) patients with basilar invagination, atlantoaxial dislocation, congenital vertebral anomalies, myelomeningocele, degenerative cervical spondylosis, or tethered cord; (4) patients with syringomyelia secondary to intracranial space-occupying lesions or hydrocephalus; (5) patients with insufficient clinical data or lack of postoperative follow-up.
Additionally, a validation cohort of 25 patients with PTDS who underwent surgical treatment at our center was included for comparative analysis. This study was conducted by the principles of the Declaration of Helsinki and was approved by the Ethics Committee of our center. Informed consent was obtained from all participants, and the work has been reported in line with the PROCESS criteria [
8].
We collected general patient data, including age, sex, smoking history, and clinical symptoms like syrinx-related manifestations, duration of symptoms, and neurological signs. Both preoperative and postoperative neurological functions were evaluated. Clinical symptoms included paresthesia, muscle atrophy, urinary and fecal incontinence, and limb weakness. Notably, some patients presented with multiple concurrent symptoms.
3. Radiographic Evaluation
A routine MRI and myelogram were conducted within 1 week before surgery. After surgery, postoperative MRI was routinely performed on a 1-month, 3-month (±1 month), 6-month (±3 months), 1-year, 1.5-year basis, and then annually until evidence of significant syrinx resolution was found. The following indicators were measured at the median sagittal and transverse T2-weighted MRI positions: (1) syrinx tension index was evaluated with maximal syrinx/cord (S/C) ratio: the ratio of syrinx diameter to the spinal cord diameter at the same level; (2) syrinx resolution rate was estimated for the maximal S/C ratio using the formula below: (preoperative value-postoperative value)/preoperative value. RadiAnt DICOM Viewer software (ver. 4.6.9, Medixant, Poland) was applied to observe and measure images.
4. Surgical Procedure
Posterior laminectomy and spinal arachnoid lysis were performed in 15 patients with IS. Meticulous microsurgical dissection was undertaken to carefully detach the thickened dorsal arachnoid tissue adherent to the spinal cord. The procedure typically commenced with the removal of the fibrotic arachnoid layer over the dorsal midline and was progressively extended laterally toward both sides, approaching the region where the dentate ligament anchors to the dura. Blunt dissection techniques were utilized to develop a natural surgical plane between the arachnoid adhesions and adjacent anatomical elements, facilitating safe and effective release. Transection of the dentate ligament was followed by the reappearance of CSF circulation and rhythmic spinal cord pulsation, serving as intraoperative confirmation of adequate decompression.
For the 25 patients with PTDS, posterior laminar decompression or osteotomy, along with subdural exploration and arachnoid adhesion lysis, were undertaken. If these approaches proved ineffective, syringomyelia shunting, such as syringo-subarachnoid, syringo-peritoneal, or syringo-pleural shunts, was considered as a final treatment option.
5. Histological Analysis
For all patients who underwent laminectomy and arachnoid lysis, the detached arachnoid tissue was formalin-fixed and paraffin-embedded during the procedure. Tissue quality was assessed using hematoxylin and eosin staining, and additional immunohistochemical staining with specific biomarkers was performed as needed.
6. Syringomyelia Symptom Evaluation
Immediate postoperative outcomes were assessed at discharge. Long-term follow-up was defined as the most recent evaluation conducted at least 6 months after surgery. Improved syringomyelia symptom outcome was defined as a sustained alleviation of preoperative symptoms. Stabilization of preoperative symptoms was classified as “no change,” while postoperative neurological deterioration was considered “deteriorated.”
7. Variable Definition
Preoperative duration of symptoms: The interval from the initial onset of symptoms to the confirmed diagnosis of syringomyelia at our institution.
Postoperative syrinx resolution: significant improvement was defined as a resolution of more than 20% in the maximal S/C ratio on follow-up MRI, while complete resolution referred to the total disappearance of the syrinx after surgery [
2,
7].
Responsible segment: The spinal segment corresponding to the posterior median incision, identified through preoperative MRI and myelography.
Scalpel sign [
9-
11]: A characteristic focal dorsal indentation of the spinal cord on MRI, resembling a scalpel blade pointing posteriorly, often indicating the presence of arachnoid webs.
Girdle sign [
9-
11]: A constricted ring formed by the thickening and adhesion of arachnoid bands, which compresses the spinal cord and creates a characteristic ring-like appearance.
For statistical analysis, IBM SPSS Statistics ver. 22.0 (IBM Co., USA) was utilized. The mean values of continuous variables were shown with standard deviations. The differences between the 2 groups of continuous variables were analyzed using the Student t-test. For dichotomous categorical data, the chi-square or Fisher exact test was used, and for multiple categorical variables, the Kruskal-Wallis H-test was used. p<0.05 means statistically significant.
RESULTS
This study included a cohort of 1,039 syringomyelia patients from a single center (
Fig. 1). After applying strict inclusion and exclusion criteria, 15 patients with IS-OAW, who underwent spinal arachnoid lysis, were identified. The average patient age was 50.1 years (range, 27–63 years), comprising 3 females and 12 males. Detailed patient characteristics, surgical types, followup status, and duration are summarized in
Table 1. All patients experienced progressively worsening neurological function, presenting with symptoms such as walking difficulties, abnormal gait, and lower limb hyperreflexia. Most also had varying degrees of paresthesia in different regions, except for cases 2, 3, 15, and 16. We highlighted 2 representative cases (cases 13 and 14) to illustrate typical imaging findings and clinical presentations (
Figs. 2A–I and
3A–O). Additionally, we included 25 patients with PTDS for comparison. These patients underwent both epidural decompression (laminar decompression or osteotomy) and subdural exploration (arachnoid adhesion lysis). Syringomyelia shunting was considered a final treatment option when these approaches were ineffective. 8 patients in the PTDS group underwent syringoperitoneal shunt surgery due to persistent or recurrent syrinx enlargement and worsening clinical symptoms despite decompression and arachnoid lysis. The clinical data, imaging features, and surgical outcomes of IS and PTDS patients were compared and summarized in
Table 2.
All patients underwent comprehensive radiographic evaluations, including MRI and computed tomography myelography, to assess CSF circulation abnormalities. Among the 15 patients, 8 presented with the characteristic “scalpel sign” on MRI, seen as a focal dorsal indentation along the spinal cord, while the remaining 7 exhibited the “girdle sign,” characterized by a constricted ring caused by arachnoid compression (
Fig. 4A–K). Preoperative myelography confirmed varying degrees of SAS obstruction, with the affected segmental levels ranging from T2 to T10, assisting in identifying the responsible segments. The mean preoperative maximal S/C ratio was 0.70±0.07 (range, 0.54–0.88), while the average syrinx shrinkage ratio at the final follow-up ranged from 12.2% to 100.0%, with a mean of 29.6% (
Table 1).
Given definite neurologic abnormalities and the obstruction of CSF circulation, posterior laminectomy and spinal arachnoid lysis were performed in 15 patients. After the dura incision, dentate ligaments were thoroughly exposed and separated, and the arachnoid adhesions of these patients were carefully dissected under a microscope until the CSF flow was completely restored and the spinal cord pulse fully reappeared.
The follow-up periods ranged from 18 months to 42 months, and the overall postoperative prognosis was favorable. No severe neurologic complications occurred in our series following surgery, while one patient developed superficial wound infections. At the last follow-up, 13 patients had a favorable syringomyeliarelated symptom outcome, which means they have sustained improvement in preoperative symptoms. Radiographic followup results showed the collapse of the syringe in most cases.
3. Histological Results
Intraoperative pathological examination and histological analysis revealed fibrosis with some meningeal cells and psammoma body calcification within the removed subarachnoid samples in all patients with IS-OAW. The pathological results of PTDS patients showed: fibrous cyst wall-like tissue, partially covered by arachnoid endothelial cells, accompanied by arachnoid endothelial cell proliferation with hyaline degeneration of interstitial fibrous tissue and a small amount of lymphocyte infiltration. The staining results of different biomarkers suggested: cytokerati (+), Ki-67 (nuclear proliferation marker) (1%+), epithelial membrane antigen (+), and somatostatin receptor 2 (+).
4. IS Group Versus PTDS Group
There was no significant difference between the 2 groups of patients in terms of age, sex, duration of syringomyelia-related natural history, etc. Patients with PTDS had a relatively higher proportion of hypesthesia and a higher syrinx tension index. In addition, there were no significant differences between the 2 groups of patients in terms of syrinx length, deviation, and location. However, patients in the IS group had significantly better postoperative syrinx resolution and syringomyelia-related symptom outcomes than those in the PTDS group.
DISCUSSION
The clinical data for this study were drawn from a prospectively maintained database of 1,039 syringomyelia patients treated at our center between December 2020 and March 2025. Of these, 15 cases of IS were retrospectively analyzed to explore optimal management strategies for this rare condition (
Supplementary Fig. 1). IS-OAW is a relatively uncommon form of the disease, characterized by syrinx formation in the absence of an identifiable cause, even after comprehensive clinical and routine radiological evaluations [
3]. The precise pathophysiology underlying arachnoid web formation remains unclear, though some researchers suggest that occult arachnoiditis may play a significant role in the development of IS [
10,
12]. It is hypothesized that these webs obstruct CSF flow, leading to syrinx formation. Mallucci et al. [
13] first identified and described occult arachnoid webs, pouches, and cysts as potential contributors to IS. Our intraoperative findings also revealed thickened arachnoid webs similar to those reported in previous studies. However, based on our direct surgical observations, these structures are more accurately described as hyperplastic transverse arachnoid septa, reflecting their distinct pathological characteristics (
Fig. 3).
IS associated with primary occult arachnoiditis is distinguished by its unclear etiology, insidious onset, atypical clinical presentation, and complex diagnostic process, making it particularly challenging to treat [
7]. In some cases, patients may remain asymptomatic, with the syrinx only identified incidentally during unrelated imaging studies [
14]. In this series, patients with IS typically presented with gradual symptom onset and nonspecific findings, leading to frequent misdiagnosis or delayed diagnosis. As a result, many were only identified at mid-to-late stages of disease progression. Clinically, IS and PTDS share similar etiologies, pathogenesis, and treatment approaches, as both involve varying degrees of subarachnoid obstruction that disrupt CSF flow. However, PTDS often follows an acute spinal cord injury (SCI) phase before progressing chronically to syringomyelia, while IS tends to develop more insidiously. In both conditions, successful treatment requires complete restoration of CSF circulation to relieve the syrinx.
The diagnosis of syringomyelia caused by occult arachnoiditis primarily relies on a combination of preoperative MRI, myelography, and intraoperative pathology [
15]. MRI remains the gold standard for syringomyelia diagnosis and is relatively sensitive for detecting arachnoiditis (
Fig. 4). Preoperative myelography can further assist in localizing the site of arachnoid obstruction and determining the responsible spinal segment [
16,
17]. However, MRI alone may miss significant CSF pathway abnormalities, particularly in the absence of overt cord distortion (e.g., case 1). Even myelography can occasionally fail to accurately pinpoint the responsible segment, especially in cases of incomplete subarachnoid obstruction (e.g., case 2). This limitation arises because focal arachnoid lesions are often confined to the dorsal SAS, potentially allowing contrast to bypass the obstructed area through the unobstructed side of the SAS [
4]. In patients with PTDS, preoperative MRI often shows abnormal CSF signal interruptions consistent with the obstructed segment identified through contrast imaging. Imaging findings also differ between IS and PTDS. IS typically presents with distinctive features like the “scalpel sign” or “girdle sign” on MRI, while PTDS often lacks such clear patterns. Intraoperatively, IS is usually associated with hyperplastic transverse arachnoid septa, while PTDS is characterized by patchy arachnoid thickening, reflecting different mechanisms of CSF circulation disruption.
Intraoperative pathology confirmed the histological characteristics of primary arachnoiditis, namely a nonspecific inflammatory lesion obstructing the SAS present in the majority of cases that were nonacute and noninfectious. At present, the inherent etiology of this intriguing occult arachnoiditis is still unclear and needs further study [
11]. The pathological profiles of PTDS and IS exhibit notable differences (
Fig. 5A–F). In PTDS, beyond arachnoid hyperplasia, there is evidence of nonspecific inflammatory exudation, likely resulting from neuroinflammatory responses triggered by acute SCI near the initial lesion site. In contrast, IS pathology is dominated by fibrosis with scattered arachnoid endothelial cells, reflecting a chronic fibrotic process with minimal inflammatory infiltration. Histologically, PTDS displays more pronounced changes, including proliferation of arachnoid endothelial cells, hyaline degeneration of the interstitial fibrous tissue, and lymphocytic infiltration-features indicative of an ongoing, active inflammatory and fibrotic response. These contrasting patterns underscore the distinct pathophysiological mechanisms of IS and PTDS: IS primarily reflects a chronic, quiescent fibrotic process, whereas PTDS represents an active phase of scarring accompanied by persistent inflammation.
The primary goal of surgical intervention in syringomyelia is to restore normal CSF circulation, either by reconstructing the SAS through decompression or by diverting CSF away from the syrinx [
7]. Treatment options for syringomyelia related to arachnoiditis include conservative management, laminectomy, arachnoid lysis, posterior fossa and foramen magnum decompression, syrinx fenestration, and shunting procedures such as syringosubarachnoid, syringoperitoneal, or syringopleural shunts [
18]. Conservative treatment might be appropriate when a patient with syringomyelia is asymptomatic or exhibits relatively mild symptoms [
19]. However, for patients with progressive syrinx enlargement and worsening neurological function, surgical intervention is often necessary. It is crucial to address the underlying pathology, such as bony anomalies or arachnoid adhesions, to improve long-term outcomes. In cases of IS-OAW, the primary surgical goal should be complete decompression of the SAS and restoration of CSF flow through meticulous arachnoid lysis.
In the absence of any anatomical abnormality and progressive neurological dysfunction attributable to a syrinx, surgical exploration with arachnoid lysis is a reasonable option, with a shunt as a last resort [
7]. Unlike CSF shunting, simple arachnoid lysis, as reported in the literature, has higher technical demands and carries a risk of postoperative readhesion [
4]. Klekamp [
4] reported that 34% of patients experienced neurological decline within 5 years following decompression, with this rate increasing to 40% within 10 years. However, if patients are appropriately selected, responsible segments are accurately identified, and SAS decompression is thorough, the prognosis can be significantly improved, avoiding the risks associated with foreign body implantation, such as tube blockage, infection, and shunt failure. Naito et al. [
20] recommended CSF shunt as a safer treatment option since arachnoid lysis is more technically demanding and associated with a high risk of postoperative neurologic deterioration due to iatrogenic meningeal scarring.
However, shunting procedures themselves carry significant risks, including fistula recurrence, catheter tip displacement, and mechanical SCI. Moreover, shunts address only the symptoms of syrinx expansion, without correcting the underlying cause of the CSF circulation disorder, often necessitating frequent surgical revisions. In contrast, several studies [
21], including ours, have demonstrated superior long-term outcomes for arachnoid lysis and duraplasty in treating arachnoid pathology compared to syrinx shunting [
22]. Guillaumet et al. [
23] similarly found that the reoperation rate for arachnoid lysis was significantly lower than for shunting procedures in their cohort.
Effective CSF circulation reconstruction requires meticulous separation of the dura mater and dentate ligament during surgery, with complete release of SAS adhesions, particularly near the denticulate ligaments. Our findings suggest that complete SAS decompression is achieved when both CSF flow is restored and intraoperative spinal cord pulsations reappear. In the early stages of our series (e.g., cases 7 and 11), our focus was primarily on restoring CSF flow. However, as our experience grew, we prioritized more comprehensive releases, ensuring spinal cord pulsations were fully restored alongside CSF recirculation. Despite overall favorable outcomes, some cases showed incomplete recovery. For instance, case 7 demonstrated persistent lower limb weakness postoperatively, and case 11 experienced progressive lower extremity weakness, with muscle strength in the distal right limb declining from grade 2 preoperatively to grade 1 postoperatively. For this case, recurrence was attributed to the formation of secondary arachnoid adhesions during the postoperative period, resulting in progressive enlargement of the syrinx. A second surgical exploration was performed, during which repeat arachnoid lysis was undertaken. Complete release of the adhesions was achieved, restoring spinal cord pulsation and re-establishing normal CSF circulation.
Comparative analysis of clinical outcomes between IS and PTDS patients revealed distinct differences in surgical approaches and prognoses. In IS, effective CSF recirculation can often be achieved through simple subdural exploration and arachnoid lysis, resulting in favorable syringomyelia resolution rates and symptom improvement. However, PTDS, characterized by an initial acute SCI phase and often accompanied by spinal fractures or deformities, presents a more challenging clinical scenario. First, the presence of vertebral fractures and spinal deformities in PTDS necessitates combined epidural bony decompression and subdural adhesion lysis to fully restore CSF pathways. Second, the localized neuroinflammatory response following acute SCI often leads to more severe and extensive arachnoid adhesions compared to IS, making complete decompression more challenging. Consequently, even with aggressive decompression, PTDS patients are more prone to long-term syrinx recurrence and require more frequent reoperations, including potential syringomyelia shunting, due to the chronic and progressive nature of their condition.
PTDS typically presents with a clear history of SCI, while IS often lacks an identifiable cause, necessitating careful differentiation from other spinal pathologies. Historically, the unclear etiology and poorly understood pathogenesis of IS have led to frequent misdiagnosis, often being mistaken for conditions like intramedullary tumors (
Supplementary Fig. 2). The etiology, clinical manifestations, and treatment strategies for syringomyelia vary depending on the underlying cause, but all forms share the common feature of abnormal CSF circulation. However, the precise pathophysiology of syringomyelia remains poorly understood. It is widely accepted that the driving force behind syrinx formation is an increase in pulse pressure within the SAS, which forces CSF through the spinal cord into the syrinx cavity [
24]. Hydrodynamic factors likely contribute to the delayed formation and gradual expansion of the syrinx after an initial cavity is established [
25].
Analogous to intracranial compliance and hydrocephalus, spinal compliance might also reflect the compensatory ability of the spinal cord to the syringomyelia [
26]. This physiological property likely plays a crucial role in the expansion of the syrinx and the subsequent development of clinical symptoms. Under normal conditions, spinal cord pulsations help maintain unobstructed CSF circulation [
27]. However, when the CSF pathway is blocked, the increased pressure gradient within the spinal cord can weaken or eliminate these pulsations, leading to progressive fluid accumulation within the syrinx. This results in characteristic structural changes, including compression, expansion, and even morphological plasticity [
28]. In our intraoperative observations, the initial spinal cord pulsations in many of these patients were significantly diminished or absent, emphasizing the importance of restoring spinal cord compliance as a critical goal in the surgical management of syringomyelia. Effective arachnoid lysis would aim not only to restore normal CSF flow but also to reestablish spinal cord pulsatility, thereby enhancing spinal autoregulation and facilitating syrinx collapse. This concept aligns with our earlier mechanistic studies on the pathophysiology of syringomyelia [
29]. Nevertheless, further prospective studies and longer follow-up periods are needed to validate this hypothesis.
This study offers valuable clinical insights into the diagnosis and management of IS-OAW by integrating preoperative imaging, intraoperative techniques, histopathological findings, and postoperative assessments. Our findings highlight the importance of accurately identifying the responsible segment to achieve complete arachnoid lysis, which is critical for improving patient outcomes in IS. Additionally, we provide a comparative analysis of IS and PTDS, emphasizing the need for tailored surgical approaches based on the underlying etiology.
However, this study has several limitations. As a retrospective analysis, it relies on the quality and consistency of clinical documentation, which may introduce variability in data collection and accuracy. Furthermore, the small sample size of patients with IS-OAW limits the generalizability of our findings and precludes the possibility of conducting randomized controlled trials. Small sample size (n=15 for IS) inherently limits statistical power. Further research with larger cohorts and prospective designs is necessary to validate our observations and refine the treatment strategies for this challenging condition.
CONCLUSION
Although both IS and PTDS are forms of syringomyelia secondary to arachnoid adhesions, they differ significantly in their pathological features, treatment strategies, and clinical outcomes. For IS with occult arachnoid webs, thorough arachnoid lysis targeting the appropriately identified responsible segment is essential for restoring spinal cord pulsations and reestablishing CSF circulation, thereby providing a relatively favorable longterm prognosis.
Supplementary Materials
Supplementary Fig. 1.
Summary of syringomyelia phenotypes on magnetic resonance imaging (MRI). (A–O) The preoperative MRI of cases with idiopathic syringomyelia with occult arachnoid webs is arranged according to case number (from case 1 to case 15). The yellow arrow indicated “scalpel sign” or “girdle sign” on MRI.
Supplementary Fig. 2.
Illustrative cases of differential diagnosis with idiopathic syringomyelia. Case 1: A 48-year-old female patient suffered from a vertebral compression fracture due to trauma. (A) She suffered numbness and weakness in both lower limbs for more than 3 years. Preoperative magnetic resonance imaging (MRI) showed syringomyelia at T5–11, and the responsible segment was located at T9. (B and C) The syringomyelia was not resolved significantly 3 months and 6 months after the operation. Case 2: The patient suffered right lower limb weakness for more than 3 years. (D) A preoperative MRI showed a thoracic syringomyelia. (E, F) The patient underwent surgical exploration of T4-T8 with the preoperative diagnosis of ependymoma at a local hospital. Pathological biopsy showed that it was not tumor tissue. Postoperative symptoms worsened, with difficulty defecation and perineal pain. The thoracic syringomyelia continues to worsen. (G) Spinal canal angiography performed in our center showed a delayed contrast agent signal above the original surgical site. He was transferred to our center for arachnoid lysis. After surgery, the symptoms were significantly relieved, and the syrinx was gradually resolved. Case 3: The patient underwent intraspinal space-occupying resection at the local hospital due to conus occlusion 2 years ago. (H) The postoperative pathology showed oligoastrocytoma. (I–L) A postoperative MRI performed 3 months ago showed syringomyelia. The patient now has urinary and defecation dysfunction, decreased pain and temperature sensation in the right upper limb, and weakness in the right lower limb. (M and N) The patient sought further treatment in our hospital, and the myelography showed that the contrast medium signal was unclear above the previous surgery segment, so local arachnoid adhesion lysis was performed in our hospital, and the symptoms improved with syrinx resolution after the operation.
NOTES
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Conflict of Interest
The authors have nothing to disclose.
-
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
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Author Contribution
Conceptualization: CL, XW, FJ; Data curation: CL, MY, FY, CD; Formal analysis: CL, FY; Methodology: CL, MY, FY, CD, XW; Project administration: CL, XW, FJ; Visualization: CL, XW, FJ; Writing – original draft: CL, MY, XW, FJ; Writing – review & editing: CL, MY, FJ.
Fig. 1.Research flow chart of this clinical series. MRI, magnetic resonance imaging; CSF, cerebrospinal fluid; SCI, spinal cord injury.
Fig. 2.Preoperative magnetic resonance imaging (MRI), myelography, and postoperative follow-up MRI of the patient in case 12. (A) Myelography showed that the contrast agent did not show clear results above the T6 segment of the thoracic spine, indicating the responsible segment. (B and C) Preoperative MRI revealed the intramedullary syrinx (the yellow arrow indicated the scalpel sign at the responsible segment of T5). Postoperative MRI done at 1 month (D and E) and 6 months (F and G) following the surgery revealed the syrinx resolution. Intraoperative arachnoid adhesion lysis (H; the yellow arrow indicated arachnoid webs) and schematic diagram of surgical operation (I): The procedure typically commenced with the removal of the fibrotic arachnoid layer over the dorsal midline and was progressively extended laterally toward both sides, approaching the region where the dentate ligament anchors to the dura. Blunt dissection techniques were utilized to develop a natural surgical plane between the arachnoid adhesions and adjacent anatomical elements. Transection of the dentate ligament was followed by the reappearance of cerebrospinal fluid pulsation and rhythmic movement of the spinal cord, serving as intraoperative confirmation of adequate decompression.
Fig. 3.Myelography, magnetic resonance imaging (MRI), histological analysis, intraoperative findings, and illustration of surgical procedures of the patient in case 13. (A, B) Myelography showed that the upper thoracic segment’s contrast medium was unclear. (C–E) Thoracic MRI revealed an intramedullary syrinx from C7 to T4 and a focal indentation at the T4 level, and the preoperative maximal syrinx/cord ratio was 0.71. (F, G) Postoperative MRI revealed syrinx resolution. (H–K) Careful adhesion separation between the thickened arachnoid and spinal cord was achieved, followed by excision of the thickened arachnoid. (L–O) Histologic analysis showed fibrous tissue hyperplasia and a few arachnoid endothelial cells with psammoma body calcification. The yellow arrow of panels D, I, and L indicated thickened arachnoid.
Fig. 4.Differential diagnosis of representative cases with the girdle sign and scalpel sign. (A and F) Myelography revealed interruption of contrast medium within the subarachnoid space of the thoracic segment, clearly indicating the site of cerebrospinal fluid obstruction. Magnetic resonance imaging demonstrated an intramedullary syrinx and identified arachnoid webs on sagittal views (B, G, and H), with representative axial images confirming their presence at the responsible segment (C, I). More enlarged and detailed examples of the girdle sign (D) or scalpel sign (J) (marked clearly with annotations). Intraoperative findings confirmed adhesion between the thickened arachnoid and the spinal cord (E and K), with additional dense arachnoid webs observed in the region corresponding to the girdle sign (E).
Fig. 5.Comparison of histopathological results between the IS and PTS groups. (A) Intraoperative pathological examination and histological analysis revealed fibrosis with some arachnoid endothelial cells in all the subarachnoid samples of IS. (B) The pathological results of PTDS patients showed arachnoid endothelial cell proliferation with hyaline degeneration of interstitial fibrous tissue and a small amount of lymphocyte infiltration. (C–F) The staining results of different biomarkers suggested: Ki-67 (1%+), CK (+), SSTR-2 (+), and EMA (+). IS, idiopathic syringomyelia; PTDS, posttraumatic delayed syringomyelia; CK, cytokerati; Ki-67, nuclear proliferation marker; SSTR-2, somatostatin receptor 2; EMA, epithelial membrane antigen.
Table 1.Summary of clinical and imaging characteristics for idiopathic syringomyelia cases who underwent arachnoid lysis included in this study
Table 1.
|
Case No. |
Symptoms & signs |
Age (yr) |
Sex |
Duration of chief complaints |
Syrinx segments |
Maximal S/C radio |
Girdle sign (MRI) |
Scalpel sign (MRI) |
Responsible segment (myelogram) |
Operative level |
Follow-up time (mo) |
Clinical outcome |
Resolution rate of syrinx |
|
1 |
Rt hand and Lt leg weakness, Rt hand numbness |
35 |
M |
4 Yr |
C3–T8 |
0.76 |
T4 |
- |
T4 |
T3-T4 |
18 |
Improved |
27.2% |
|
2 |
LE weakness, urinary and fecal incontinence |
59 |
M |
3 Yr |
T1–11 |
0.71 |
T7 |
- |
T7 |
T5-T7 |
18 |
Improved |
26.4% |
|
3 |
LE weakness and Rt hand pain |
61 |
M |
2 Yr |
C7–T3 |
0.65 |
T3 |
- |
T3 |
T3-T5 |
18 |
Improved |
24.2% |
|
4 |
LE, thoracic and lumbar numbness |
63 |
M |
2 Yr |
T4–11 |
0.70 |
T7 |
- |
T7 |
T7-T9 |
18 |
Improved |
28.5% |
|
5 |
LE weakness and hypaesthesia |
52 |
F |
4 Yr |
C7–L1 |
0.72 |
- |
T5 |
T5 |
T3-T5 |
18 |
Improved |
29.3% |
|
6 |
LE weakness and Lt lumbar dysesthesia |
32 |
M |
10 Yr |
C5–T9 |
0.75 |
- |
T7 |
T7 |
T7-T8 |
36 |
Improved |
29.1% |
|
7 |
Weakness of Lt lower limb and numbness of LE |
27 |
M |
6 Yr |
C4–T11 |
0.64 |
T7 |
- |
T8 |
T7-T9 |
42 |
No Change |
14.3% |
|
8 |
LE weakness and hypaesthesia |
52 |
M |
19 Yr |
T2–7 |
0.61 |
T5 |
- |
T5 |
T4-T6 |
36 |
Improved |
18.4% |
|
9 |
LE weakness, Rt leg and lumbar numbness |
54 |
M |
2 Yr |
T2–12 |
0.70 |
- |
T10 |
T10 |
T9-T11 |
36 |
Improved |
23.7% |
|
10 |
Thoracic girdle sensation, LE weakness |
56 |
M |
4 Yr |
C1–T11 |
0.65 |
- |
T5 |
T5 |
T3-T5 |
24 |
Improved |
24.2% |
|
11 |
Weakness and numbness of Rt leg |
59 |
F |
10 Yr |
C7–T9 |
0.77 |
T6 |
- |
T6 |
T5-T7 |
36 |
Deteriorated |
12.2% |
|
12 |
Numbness of Rt upper limbs |
32 |
M |
2 Mo |
C75 |
0.80 |
|
T5 |
T5 |
T5 |
18 |
Improved |
100% |
|
13 |
Hyperesthesia of pain and temperature in the Lt limbs |
60 |
M |
1 Yr |
C7–T4 |
0.71 |
|
T4 |
T4 |
T3-T4 |
18 |
Improved |
47.2% |
|
14 |
LE weakness |
59 |
M |
2 Yr |
T7–9 |
0.76 |
|
T3 |
T3 |
T10-T12 |
18 |
Improved |
19.6% |
|
15 |
Weakness of Rt lower limb |
51 |
F |
1 Yr |
T2–8 |
0.54 |
|
T6 |
T6 |
T4-T6 |
18 |
Improved |
20.3% |
Table 2.Summary of the radiologic and neurologic outcome for cases included in this study
Table 2.
|
Variable |
IS (n = 15) |
PTDS (n = 25) |
T/H/χ2 value |
p-value |
|
Age (yr) |
50.1 ± 11.8 |
49.8 ± 8.5 |
0.089 |
0.930 |
|
Male sex |
12 |
15 |
0.919 |
0.338 |
|
Smoking |
11 |
8 |
6.423 |
0.011*
|
|
Symptom duration of SM (mo) |
56.1 ± 57.4 |
34.2 ± 24.3 |
1.633 |
0.111 |
|
New presenting symptoms of SM |
|
|
|
|
|
Neuropathic pain |
1 |
3 |
0.000 |
1.000 |
|
Dysesthesia |
9 |
15 |
0.000 |
1.000 |
|
Hypesthesia (elevated sensory level) |
2 |
14 |
7.111 |
0.008*
|
|
Weakness (decreased motor power) |
12 |
16 |
0.508 |
0.476 |
|
Other symptoms |
|
|
|
|
|
Gait disorder (ataxia) |
3 |
8 |
0.209 |
0.648 |
|
Sphincter dysfunction |
1 |
7 |
1.500 |
0.221 |
|
Scoliosis |
2 |
3 |
0.000 |
1.000 |
|
Preoperative syrinx |
|
|
|
|
|
Maximal S/C (%) |
69.8 ± 6.7 |
77.4 ± 11.2 |
-2.342 |
0.025*
|
|
Syrinx length (segment) |
9.1 ± 4.2 |
11.4 ± 3.4 |
-1.856 |
0.071 |
|
Syrinx location |
|
|
1.099 |
0.294 |
|
Cervic-thoracic |
8 |
18 |
|
|
|
Thoracic |
6 |
5 |
|
|
|
Holocord |
1 |
2 |
|
|
|
Syrinx deviation |
|
|
0.000 |
1.000 |
|
Central |
13 |
22 |
|
|
|
Deviated |
2 |
3 |
|
|
|
Surgery duration |
201.2 ± 49.9 |
213.5 ± 54.7 |
-0.728 |
0.472 |
|
Intraoperative blood loss |
58.7 ± 45.3 |
84.4 ± 43.7 |
-1.762 |
0.089 |
|
Syringomyelia symptom outcome |
|
|
6.500 |
0.011*
|
|
Improved |
13 |
11 |
|
|
|
No change |
1 |
7 |
|
|
|
Deteriorated |
1 |
7 |
|
|
|
Syrinx resolution |
|
|
4.177 |
0.041*
|
|
Resolved effectively (≥ 20%) |
11 |
10 |
|
|
|
Resolved not effectively (< 20%) |
4 |
15 |
|
|
REFERENCES
- 1. Greitz D. Unraveling the riddle of syringomyelia. Neurosurg Rev 2006;29:251-63. discussion 264.
- 2. Williams H. A unifying hypothesis for hydrocephalus, Chiari malformation, syringomyelia, anencephaly, and spina bifida. Cerebrospinal Fluid Res 2008;5:7.
- 3. Lin JW, Lin MS, Lin CM, et al. Idiopathic syringomyelia: case report and review of the literature. Acta Neurochir Suppl 2006;99:117-20.
- 4. Klekamp J. Treatment of syringomyelia related to nontraumatic arachnoid pathologies of the spinal canal. Neurosurgery 2013;72:376-89. discussion 389.
- 5. Brickell KL, Anderson NE, Charleston AJ, et al. Ethnic differences in syringomyelia in New Zealand. J Neurol Neurosurg Psychiatry 2006;77:989-91.
- 6. Sakushima K, Tsuboi S, Yabe I, et al. Nationwide survey on the epidemiology of syringomyelia in Japan. J Neurol Sci 2012;313:147-52.
- 7. Roy AK, Slimack NP, Ganju A. Idiopathic syringomyelia: retrospective case series, comprehensive review, and update on management. Neurosurg Focus 2011;31:9.
- 8. Agha RA, Sohrabi C, Mathew G, et al. The PROCESS 2020 Guideline: updating consensus Preferred Reporting Of Cas-ESeries in Surgery (PROCESS) Guidelines. Int J Surg 2020;84:231-5.
- 9. Reardon MA, Raghavan P, Carpenter-Bailey K, et al. Dorsal thoracic arachnoid web and the “scalpel sign”: a distinct clinical-radiologic entity. Am J Neuroradiol 2013;34:1104-10.
- 10. Voglis S, Romagna A, Germans MR, et al. Spinal arachnoid web-a distinct entity of focal arachnopathy with favorable long-term outcome after surgical resection: analysis of a multicenter patient population. Spine J 2022;22:126-35.
- 11. Delgardo M, Higgins D, McCormick KL, et al. Clinical characteristics, outcomes, and pathology analysis in patients with dorsal arachnoid web. Neurosurgery 2022;90:581-7.
- 12. Sayal PP, Zafar A, Carroll TA. Syringomyelia secondary to “occult” dorsal arachnoid webs: report of two cases with review of literature. J Craniovertebr Junction Spine 2016;7:101-4.
- 13. Mallucci CL, Stacey RJ, Miles JB, et al. Idiopathic syringomyelia and the importance of occult arachnoid webs, pouches and cysts. Br J Neurosurg 1997;11:306-9.
- 14. Nakamura M, Ishii K, Watanabe K, et al. Clinical significance and prognosis of idiopathic syringomyelia. J Spinal Disord Tech 2009;22:372-5.
- 15. Brodbelt AR, Stoodley MA. Syringomyelia and the arachnoid web. Acta Neurochir (Wien) 2003;145:707-11. discussion 711.
- 16. Aubin ML, Baleriaux D, Cosnard G, et al. MRI in syringomyelia of congenital, infectious, traumatic or idiopathic origin. A study of 142 cases. J Neuroradiol 1987;14:313-36.
- 17. Scotti G, Scialfa G, Landoni L, et al. Nuclear magnetic resonance in the diagnosis of syringomyelia. J Neuroradiol 1984;11:239-48.
- 18. Gallo P, Kaliaperumal C. The management of idiopathic and refractory syringomyelia. Adv Tech Stand Neurosurg 2022;45:317-38.
- 19. Olsson L, Antepohl W, Ravn SL. Active conservative management of primary spinal syringomyelia: a scoping review and perspectives for an activity-based clinical approach. J Rehabil Med 2022;54:jrm00322.
- 20. Naito K, Yamagata T, Ohata K, et al. Safety and efficacy of syringoperitoneal shunting with a programmable shunt valve for syringomyelia associated with extensive spinal adhesive arachnoiditis: technical note. World Neurosurg 2019;132:14-20.
- 21. Ghobrial GM, Dalyai RT, Maltenfort MG, et al. Arachnolysis or cerebrospinal fluid diversion for adult-onset syringomyelia? A systematic review of the literature. World Neurosurg 2015;83:829-35.
- 22. Klekamp J, Batzdorf U, Samii M, et al. Treatment of syringomyelia associated with arachnoid scarring caused by arachnoiditis or trauma. J Neurosurg 1997;86:233-40.
- 23. Guillaumet G, Aghakhani N, Morar S, et al. Reintervention rate of arachnolysis versus shunting for nonforaminal syringomyelia. J Neurosurg Spine 2021;34:673-9.
- 24. Taylor DG, Chatrath A, Mastorakos P, et al. Cerebrospinal fluid area and syringogenesis in Chiari malformation type I. J Neurosurg 2020;134:825-30.
- 25. Shields CB, Zhang YP, Shields LB. Post-traumatic syringomyelia: CSF hydrodynamic changes following spinal cord injury are the driving force in the development of PTSM. Handb Clin Neurol 2012;109:355-67.
- 26. Pang D, Altschuler E. Low-pressure hydrocephalic state and viscoelastic alterations in the brain. Neurosurgery 1994;35:643-55. discussion 655-6.
- 27. Burman R, Alperin N, Lee SH, et al. Patient-specific craniospinal compliance distribution using lumped-parameter model: its relation with ICP over a wide age range. Fluids Barriers CNS 2018;15:29.
- 28. Brasil S, Solla DJF, Nogueira RC, et al. Intracranial Compliance assessed by intracranial pressure pulse waveform. Brain Sci 2021;11:971.
- 29. Lu C, Wu X, Wang X, et al. Single-cell transcriptomics reveals ependymal subtypes related to cytoskeleton dynamics as the core driver of syringomyelia pathological development. iScience 2023;26:106850.
