Abstract

Background: Chiari malformation type 1 (CM-1) with syringomyelia is a common craniocervical abnormality and in symptomatic patients, there is ongoing debate regarding the optimum surgical strategy for decompressing the foramen magnum. The placement of a fourth ventricular-subarachnoid stent is a novel approach intended to increase symptom response rates and decrease the need for revision surgery, particularly in complex cases. The aim of this study was to present a single-center experience on the safety and efficacy of this technique.

Methods: A retrospective review was conducted of all CM-1 patients who underwent Foramen Magnum Decompression (FMD) + fourth ventricular stent between January 01, 2012, and September 20, 2022, at a single UK neurosurgical center. Patients were identified using a keyword search of the hospital’s electronic medical records. Primary outcomes included syrinx size and neurological symptoms. Secondary outcomes included operative duration, length of stay, and number of revision procedures. Syrinx size was measured on axial T2 magnetic resonance imaging sequences.

Results: 17 patients received a stent as part of their FMD. The use of a stent improved or resolved the radiological appearance of the syrinx in 16 (87.5%) patients with an average AP diameter reduction of 57% (−4.86 mm standard deviation: 3.32). Clinically, 8 (62%) patients reported complete or partial resolution of limb symptoms. Following stent-assisted FMD only, 2 patients (11.7%) required further decompressive surgery.

Conclusion: This case series evaluates the use of a fourth ventricular stent as part of FMD for CM-1. The study demonstrates the efficacy of a stent with satisfactory radiological and clinical outcomes. The results support the use of fourth ventricular stenting as a useful adjunct in patients with complex obstruction of fourth ventricle outflow.

Keywords: Chiari malformation, Foramen magnum decompression, Syringomyelia, Syrinx

INTRODUCTION

Chiari malformation type 1 (CM-1) is the most commonly diagnosed craniocervical malformation.[ 9 , 15 , 27 , 30 ] The resulting cerebellar tonsillar herniation can obstruct the normal flow of cerebrospinal fluid (CSF) at the level of the foramen magnum with subsequent dissociation of cranial–spinal CSF pressure.[ 9 , 15 , 27 , 30 ] Syringomyelia formation is one sequelae of this disordered CSF flow with several proposed theories, although no consensus, on its pathogenesis.[ 20 , 29 , 47 ]

The most widely accepted theory is Gardner’s hydrodynamic theory.[ 19 , 21 ] Gardner attributed the pathogenesis of syringomyelia to CSF moving from the fourth ventricle through the spinal cord central canal due to craniospinal pressure differentials in the presence of fourth ventricular outlet obstruction. William’s theory[ 54 ] builds on Gardner’s hydrodynamic phenomena and demonstrates these craniospinal pressure differentials in patients with hindbrain anomalies through manometric pressure measurements.[ 54 ] Alternatively, Ball and Dayan[ 4 ] used cadaveric data to propose that CSF enters the spinal cord to create a syrinx through the subarachnoid space along Virchow–Robin spaces. Finally, in more recent years, amalgamations of these theories such as Pillay et al.’s universal revised hydrodynamic theory have been proposed and incorporate magnetic resonance imaging (MRI)-based data.[ 45 ]

Foramen magnum decompression (FMD) is effective in providing both anatomical decompression and symptom alleviation by restoring CSF flow across the craniocervical junction.[ 26 , 40 ] It is also effective in reducing the pressure exerted by syringomyelia on the spinal cord.[ 17 , 30 , 41 , 56 ] A previous systematic review showed that FMD (and variations of this approach) improves signs and symptoms of syrinx-associated CM-1 in 79.95% of 1,242 patients.[ 56 ] Other studies have demonstrated favorable clinical outcomes post-FMD in up to 90% of patients.[ 10 ] It is thought that this is due to the normalizing of pulsatile and static increased intracranial pressure and the normalization of craniospinal pressure dissociation.[ 17 ]

However, despite FMD being an accepted surgical strategy, there is an ongoing debate over optimum techniques including variations such as bone-only decompression, duraplasty, and tonsillar resection.[ 30 , 40 , 35 , 43 ] Additional salvage methods for addressing the syrinx include syringopleural shunting,[ 2 ] syringostomy,[ 36 ] obexostomy,[ 37 ] syringo-subarachnoid,[ 3 ] and fourth ventriculosubarachnoid shunting.[ 26 ]

The re-intervention rate following FMD for CM-1 with syrinx is between 7% and 11%.[ 7 , 31 , 34 , 49 ] However, this rate may vary based on the technique used: bone-only decompression (18%), durotomy (5%), or duraplasty (6%).[ 22 ] An emerging approach for refractory syringomyelia following previous FMD surgery involves the placement of a stent through the foramen of Magendie to ensure the patent flow of CSF between the fourth ventricle and the spinal subarachnoid space.[ 46 ] A previous case series of 14 patients with recurrent or expanding syringomyelia following a CM-1 FMD found that placing a stent resulted in >90% of patients achieving a meaningful reduction in syrinx size.[ 46 ] The aim of this study was to present our center’s experience of fourth ventricular stenting in FMD and further contribute to this growing evidence base.

MATERIALS AND METHODS

A retrospective review was conducted of all patients who underwent an FMD with a fourth ventricular stent between January 01, 2012, and September 20, 2022, at a single UK tertiary neurosurgical center (University Hospital Southampton NHS Foundation Trust). Patients were identified using a keyword search of the hospital’s electronic record database using the search: “(FMD OR Decompression OR Foramen Magnum Decompression) AND (stent OR stenting).” Those patients identified as receiving a stent as part of a primary or revision FMD were eligible for inclusion in the study. There was no age restriction set on eligibility. No further inclusion criteria were set to capture the center’s entire experience. All identified patients underwent case note review including operation notes, discharge summaries, clinic letters, and radiology reports.

Syrinx size was measured on axial T2 MRI sequences by recording the widest AP diameter of the syrinx. Measurements were obtained from the radiology reports provided by consultant neuroradiologists. Postoperative clinical outcomes were categorized as resolved, improved, unchanged, or worse, with reference to their preoperative severity. All clinical and radiological outcomes were measured 12-month postsurgery or immediately before a revision surgery, whichever was sooner.

Statistical analysis was performed using descriptive methods with the Statistical Package for the Social Sciences version 1.0. 0.1275. The data that support the findings of this study are available from the senior author (AC) upon reasonable request. The data that support the findings of this study are available from the corresponding author, CT, upon reasonable request. The requirement for ethical approval was waived by the local ethical committee owing to the retrospective secondary nature of the data collection.

Standard procedure for CM-1

Standard procedure for patients with CM-1 has historically been an area of controversy due to heterogeneous patient presentation and the variety of surgical techniques.[ 44 ] Some support the concept of bony decompression and duraplasty for all patients whilst others advocate for a more individualized process.[ 27 , 44 , 52 ] Locally, we implement a patient-specific approach based on radiological and clinical factors. Procedures are generally performed prone, with the head in a neutral position. A midline incision is made from the external occipital protuberance to the spinous process of C2. The suboccipital planum, foramen magnum, and posterior arch of C1 are identified. The atlantooccipital ligament is removed and a craniotomy is performed to extend the foramen magnum with or without a C1 laminectomy. The patients then undergo one of the following procedures: durasplitting (only the outer dural layer is incised or removed), duraplasty (the dura is opened and arachnoid left closed), FMD with arachnoid opening (in the case of significant arachnoid scarring/adhesions), and tonsillar resection (if deemed necessary due to significant tonsillar descent).

RESULTS

Baseline characteristics

The search of the hospital online databases across the 10-year period returned 184 patients who underwent an FMD or revision FMD within this date range of which 17 patients (9.2%) received a stent as part of their surgery [ Figure 1 ]. Thirteen (76%) of the patients were female and 6 (35%) were younger than 18 years old (pediatric) at the time of stenting. The mean age of pediatric patients was 8 (standard deviation [SD]: 5.49) years and the mean age of adult patients was 31 years (SD: 11.03). The average body mass index (BMI) at the time of surgery was 31.66 (SD: 10.81) [ Table 1 ].

Figure 1:

A flow diagram indicating patient identification and selection for inclusion. Foramen magnum decompression (FMD).

Table 1:

Patient demographics, previous surgeries, and co-morbidities.

Four patients received the stent during a primary FMD and the remaining 13 were done during a revision FMD. Of the 13 who received the stent during a revision FMD, eight had undergone one previous FMD and five had undergone two previous FMDs [ Table 1 ].

Indications

The four patients who received the stent during their primary operation did so as it was deemed intraoperatively by the surgeon that adequate CSF flow could not be achieved by standard FMD ± durotomy. Indications for the 13 stented revisions included refractory/worsening syrinx (n = 10, 76.9%), persistent neurological deficit (n = 2, 15.4%), and wound exploration for persistent CSF leak (n = 1, 7.7%) [ Table 2 ]. The type of previous FMD is shown in Table 1 .

Table 2:

Stenting operation and poststent follow-up surgery/complications.

Procedure

The mean operative duration of FMD + stent was 171 min (SD: 60). This was not significantly different from the FMDs without a stent performed previously in the same patient group (142 min, P = 0.70). The average length of stay following a stent was 6.2 days (SD: 1.64) which also was not significantly different from the nonstented FMD procedures in the same patients (6.2 days, P = 0.48). The average stent length was 5.57cm (SD: 0.98).

All operations used a Codman® BACTISEAL® EVD AntiMicrobial Catheter inserted through the foramen of Magendie into the fourth ventricle with the distal end lying in the spinal subarachnoid space [ Figure 2 ]. The fourth stent was sutured to the pseudomeningocele/dura to prevent migration. Additional holes were cut into the side of the catheter along its length to aid CSF flow. A full description of the technique can be found in Han et al.[ 28 ] The stent is generally inserted approximately 2 cm into the fourth ventricle, with the distal end 1–2 cm into the cervical subarachnoid space, usually at or below the level of the tonsils. A full dural opening is often performed in all patients, followed by an autologous duraplasty. This technique was not deviated from unless explicitly stated.

Figure 2:

An anatomical diagram of stent placement. (a) Stent Placed in the fourth ventricle and cervical subarachnoid space. (b) Subsequent resolution of the syrinx.

Syrinx outcomes

The preoperative syrinxes spanned a mean of 10 vertebral levels, ranging from a single level at T5 to the largest at C4– L1. Before stenting, the average syrinx AP diameter was 8.53 mm (SD: 3.22) [ Table 3 ].

Table 3:

Postoperative change in syrinx size.

Poststent, the average syrinx AP diameter was 3.73 mm (SD: 3.42). This was a mean reduction of −4.86 mm (SD: 3.32). Syrinx AP diameter pre and poststent were significantly different (8.53 mm vs. 3.73 mm, P < 0.001). The presence of the syrinx was qualitatively reported within radiological reports as improved/resolved in 14 (87.5%) of patients. Pre and postoperative imaging showing syrinx resolution and stent location is shown in Figure 3 .

Figure 3:

(a and b) Pre and postoperative magnetic resonance imaging showing syrinx resolution and stent location (red arrow) for two patients.

Clinical outcomes

Before stenting, four (23.5%) patients reported no neurological symptoms, 10 (58.8%) reported upper limb symptoms, and 10 (58.8%) reported lower-limb symptoms [ Table 4 ]. Of the 13 patients with some preoperative limb neurology, three (23%) had full resolution poststent, six (46%) were improved, and four (31%) were unchanged at the final 12-month follow-up. The four patients with no neurological symptoms received a stent due to radiological syrinx progression/failure of syrinx resolution from previous FMD attempts.

Table 4:

Limb symptoms before and after stenting.

Poststent surgery and complications

Following stent insertion 15 patients (88.3%) did not require further surgery at the foramen magnum. However, two patients (11.7%) required a revision FMD for progression of the syrinx [ Table 2 ].

Eight (47%) patients sustained a complication of which the most common (n = 6) was CSF leak. All six of these patients were at the extremes of weight, five were obesity class 3 (BMI >40.0) and one was underweight (BMI <18.5). Four were managed with CSF diversion (lumboperitoneal or ventriculoperitoneal [VP] shunts) and two underwent revision of the wound without CSF diversion. Of these two patients, both had undergone prior FMDs at other institutions with poor outcomes and one had severe platybasia with complex aberrant base of skull anatomy. Two further patients sustained a transient deterioration in neurological function. One of whom had a House Brackmann grade III facial nerve palsy from migration of the spinal component into the pseudomeningocele causing the orientation of the fourth ventricular component to abut the facial colliculus. This required relocation of the stent with complete resolution of the facial paresis. The other sustained a neurogenic bladder requiring a Mitrofanoff procedure which subsequently resolved. No patients had a permanent new neurological deficit.

This study assessed clinical and radiological outcomes at a 12-month follow-up, which provides insight into early and mid-term effectiveness of fourth ventricular stenting. However, longer-term outcomes beyond this period were not systematically evaluated. Given the potential for delayed complications such as stent migration, re-occlusion, or recurrence of syringomyelia, further studies with extended follow-up are needed to assess the durability of symptom relief and syrinx resolution over time. Future research should aim to track long-term stability of outcomes and identify any late-onset adverse effects associated with this technique. Anecdotally, at the time of submission, one patient represented 8-year postoperatively, with slight caudal migration of the stent.

The overall complication rate observed in this study (47%) is greater than the upper limit currently reported in the literature (3–40%).[ 44 ] This may be due to this study only including patients with complex pathology, multiple prior FMD attempts, and refractory syrinxes. The increased complication rate is likely influenced by preexisting scar tissue, altered CSF flow dynamics, and anatomical challenges unique to revision surgery. In addition, a disproportionate number of CSF leaks occurred in patients with extreme BMI, suggesting that patient-specific factors may also contribute. While stenting may reduce the need for further decompression surgeries, future studies should explore strategies to minimize complications, particularly CSF leaks, in this subset of patients.

DISCUSSION

There are several surgical variations when decompressing the foramen magnum for patients with CM-1. The variations include bone-only decompression, durotomy, duraplasty, and tonsillar resection.[ 6 , 18 , 22 ] A lower revision rate has been seen following procedures incorporating a durotomy.[ 22 , 33 ] Recently, there has been a growing emergence of fourth ventricular stenting as part of the operative management in complex patients with refractory syrinxes and Magendie obstruction.[ 12 , 28 , 46 , 48 , 50 , 55 ]

It has previously been suggested that stents are only required when a webbed or scarred arachnoid is seen to block the foramen of Magendie and that intradural pathology, in particular arachnoid veils, play a vital role in the pathophysiology of CM-1-associated syringomyelia.[ 11 , 25 , 56 ] The role of the arachnoid in FMD failure is therefore of increasing interest.[ 11 , 51 ] Previous studies have suggested that the addition of arachnoid dissection/adhesionolysis reduces reoperation rates by 70% and results in a 75% less likelihood of clinical deterioration postoperatively.[ 8 ] This is supported by findings of greater clinical recurrence rates attributed to profound arachnoid pathology[ 30 ] and the observation of foraminal arachnoiditis in over half a patient cohort (n = 35) undergoing revision FMDs.[ 31 ] However, arachnoid dissection may lead to greater complication rates and re-hospitalization [ 43 ] and two systematic reviews[ 44 , 42 ] did not find a significant benefit on syrinx size following arachnoid dissection.[ 25 ]

The evidence discussing the efficacy of fourth ventricle stenting is limited to case series; however, promising results have been reported with clinical improvement rates of approximately 75%.[ 28 , 46 ] However, additional morbidity from complications that would not normally be experienced with nonstent FMD surgery, such as stent migration and improper placement, has been reported.[ 46 , 48 ]

It is worth noting that atlantoaxial instability (AAI) is a recognized cause of failed FMD.[ 23 , 24 ] In this study, patients were not individually assessed for this; however, no patients were known to have AAI. In this sub-group, the current literature suggests that patients may benefit from fixation rather than a stent as studies indicate AAI as the nodal point of Chiari pathogenesis and that atlantoaxial fixation is the most effective intervention.[ 23 ]

Patient selection is an important consideration when interpreting study outcomes.[ 38 ] The patients included in the current study were all re-operations or those with poor fourth ventricle outflow noted during the primary procedure. Potentially, the reason for failure of the primary nonstenting FMD was also poor fourth ventricle outflow which was not appreciated during the primary procedure. Thus, the addition of a stent is potentially best used for select cases with an obstructed fourth ventricular outflow which may otherwise be at a higher risk of failure due to the orientation of CSF flow from the fourth ventricle preferring to enter the obex as opposed to the foramen of Magendie. The authors suggest that this technique enables the stent to act as a physical barrier over the obex to disrupt the pulsatile waves of CSF which is maintained even if Magendie was to re-occlude. The additional perforations may provide a durable route for CSF to flow out of Magendie; however; as Luschka remains open, the authors believe that the stent over the obex is the more important mechanism by which the stent works.

Syrinx reduction

This study found that the use of a stent significantly reduced the AP diameter of the syrinx by −4.86 mm with 87.5% of patients experiencing either partial or complete resolution of the syrinx. This may be clinically significant when considering that a reduction in syrinx size may be considered a surrogate for the reduction in internal pressure exerted on the spinal cord.[ 5 , 29 ] This association has been historically evidenced by studies showing that syrinxes are associated with raised intramedullary pressures which may worsen/induce neurological symptoms due to long-tract compression and compressions of neurons and microcirculation.[ 48 ]

These findings are consistent with Riordan and Scott[ 46 ] where stenting eliminated or reduced the syrinx by ≥75% in 93% of patients. Han et al. also reported that among their 13 patients’ series, stenting resulted in a 75% reduction in syrinx area, and in 81% of patients, the syrinx reduced by at least 50%.[ 28 ] Finally, Sun et al.[ 51 ] also reported attenuation and symptom resolution in all four patients who received a stent.

Despite these favorable findings supporting the addition of a stent, these syrinx resolution rates are also similar to those of a previous meta-analysis[ 13 ] and case series of FMD ± duraplasty alone.[ 53 ] Durham and Fjeld-Olenec ,[ 13 ]Kumar et al. ,[ 33 ] Wang et al. ,[ 53 ] and Mutchnick et al. [ 40 ] report syrinx resolution rates of 71–92%. However, it is not known what the syrinx resolution rate would be in the subgroup of patients with more complex fourth ventricle outflow obstruction and the addition of the stent may be necessary in these select cases to match the resolution rates seen in uncomplicated cases.

Neurological symptoms

Within this study, of the 13 patients with preoperative neurological symptoms, 69% reported resolution or improvement in symptoms after receiving a stent. Symptom resolution was seen most frequently in those who also experienced syrinx resolution or improvement. Previous studies of patients with a syrinx report an improvement in neurological symptoms of 88-98% of patients following FMD.[ 28 ] The discrepancy between the statistically significant reduction in syrinx size and the lower rate of symptom resolution (69%) is likely an artifact of the study’s small sample size and retrospective design. With a limited cohort, variability in clinical outcomes may be amplified. In addition, given the reliance on clinical notes, assessing symptom improvement retrospectively is inherently limited, as documentation may lack consistency and objectivity. In contrast, radiological changes could be measured objectively, allowing for a more precise evaluation of syrinx resolution. While it is possible that some patients experienced irreversible spinal cord damage due to prolonged compression, this was not systematically assessed in our study, and it would not be appropriate to extrapolate this conclusion from the available data. Future prospective studies with standardized clinical assessments are needed to clarify the relationship between syrinx resolution and functional outcomes. While the discrepancy between radiological improvement and symptom resolution should be considered in patient selection, it remains unclear how predictive syrinx resolution is for clinical recovery.

The lower symptom resolution rate in the stent cohort likely reflects that this patient cohort represents those with more challenging pathology and more established irreversible spinal cord damage as the majority of these patients are undergoing redo FMD. This may, in keeping with current reports, suggest that stenting should be reserved for only those with complex fourth ventricular outflow or those who do not achieve resolution after primary FMD ± duraplasty alone.[ 28 ] This is in keeping with the results of Sun et al. who concluded that stenting should be reserved only as a revision procedure, especially if the foramen of Magendie is occluded by arachnoid adhesions or as a primary procedure if decompression is not sufficient and CSF flow cannot be guaranteed.[ 51 ]

The determination of a complex obstruction of fourth ventricular outflow and potential eligibility for a stent is based on a combination of clinical, radiological, and intraoperative factors rather than a single preoperative criterion. Patients with atypical clinical presentations, a history of previous FMD attempts, or challenging radiological features should alert the operating surgeon to the possibility of a complex case that may be suitable for stenting. However, intraoperative findings often provide the most definitive assessment, particularly when direct visualization reveals persistent obstruction despite decompression as described by Sun et al.[ 51 ] Future studies may benefit from standardized criteria to guide decision-making in these complex cases.

Surgical considerations

Length of operation and hospital stay vary depending on the surgical approach. For example, operation time and duration of stay are significantly reduced in patients who undergo a dura-splitting FMD compared to those who receive FMD with duraplasty.[ 8 ] Our study suggests that the addition of a stent does not cause a significant increase in operative duration compared to FMD alone, nor does it increase, the length of hospital stay.

Placement of a stent has been associated with several complications.[ 28 , 46 ] Riordan and Scott found that two (14%) patients suffered from late stent dislodgement and one (7%) had a neurological deficit (mild unilateral dorsal column deficit), which is similar to the 6% reported in the present study.[ 46 ]

It is also worth drawing comparison to the previously described Torkildsen shunt.[ 1 , 14 ] First described in 1939, the Torkildsen shunt was a pioneering technique involving the diversion of CSF from the lateral ventricle to the cisterna magna through a suboccipital craniotomy and a tract through the occipital horn of the lateral ventricle.[ 1 , 14 ] It was primarily used in cases of obstructive hydrocephalus, aiming to bypass the aqueductal blockage by restoring CSF flow from the supratentorial to the infratentorial compartments.[ 39 ] While conceptually similar in its goal of reestablishing CSF circulation, the Torkildsen shunt differs from the present approach in both anatomical targeting, technique, and surgical indication. The present method focuses on correcting dynamic flow abnormalities and pressure dissociation specific to the craniocervical junction in Chiari I malformation and syringomyelia, rather than serving as a global CSF diversion procedure. Moreover, the Torkildsen shunt fell out of favor due to its invasive nature and the advent of VP shunting, the current technique offers a somewhat more localized and potentially more physiologically compatible intervention aimed at restoring craniospinal compliance.[ 16 , 39 ] Nevertheless, the historical precedent of the Torkildsen shunt underscores the longstanding neurosurgical interest in manipulating CSF pathways to treat complex pathologies.

Before receiving a stent, 76% of patients included in this study had undergone at least one prior FMD. However, after receiving a stent, only 11.7% (n = 2) of patients required a revision FMD. This is comparable to the previously reported stent revision rate by Riordan and Scott of 14%.[ 46 ] However, this study lacks a direct comparative group, as stenting was selectively performed in complex or refractory cases where standard FMD was deemed insufficient. Given the rarity of this technique, assembling a matched cohort for statistical comparison was not feasible. It is also lower than the average nonstent FMD revision rate of 18–32%.[ 22 , 32 ] These data suggest that the use of a stent may reduce the need for further FMD surgery, particularly in those with refractory syrinx, although the numbers are too small to make definitive conclusions.

Limitations

This study is limited by its retrospective nature and a small cohort size. Given that it represents 10 years of practice on an uncommonly required technique, it would be impractical to prospectively collect a large enough cohort to conclude on. The group is a heterogeneous mixture of adults and pediatrics and primary and revision surgeries. The study cohort includes primary and revision procedures. Of the 17 patients, 13 underwent stent placement as part of a revision FMD, primarily due to persistent or worsening syringomyelia or neurological symptoms following an initial decompression. This selection inherently favors cases with more complex pathology or refractory CSF flow obstruction, which may bias the cohort toward more severe cases. As a result, the outcomes observed – both in terms of clinical response and syrinx resolution – may not be directly generalizable to patients undergoing a first-time FMD. However, the numbers are too small to separate into subgroups and need to be combined to make general conclusions about the outcomes. A further limitation of this study is the inability to determine the total number of CM-1 patients with failed prior decompression surgeries treated at our center during the study period.

CONCLUSION

This study demonstrates that fourth ventricular stenting as part of FMD for CM-1 produces satisfactory radiological and clinical outcomes. The use of fourth ventricular stenting may thus be a useful adjunct in patients with complex obstruction of the fourth ventricle outflow. This operative technique may be best suited for those with complex obstruction of the fourth ventricle, arachnoid adhesions, a re-occluding foramen of Magendie, or if primary standard approaches are deemed insufficient to ensure adequate CSF dynamics.

Ethical approval:

Institutional Review Board approval is not required. The requirement for ethical approval was waived by the local ethical committee owing to the retrospective secondary nature of the data collection.

Declaration of patient consent:

Patient’s consent is not required as there are no patients in this study.

Financial support and sponsorship:

Publication of this article was made possible by the James I. and Carolyn R. Ausman Educational Foundation.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

References

1. Aarli JA. Arne thorkildsen and thorkildsen’s surgery [Arne Thorkildsen and Thorkildsen’s surgery]. Tidsskr Nor Laegeforen. 2000. 120: 3726-7

2. Akakın A, Yılmaz B, Ekşi MŞ Kılıç T. Treatment of syringomyelia due to Chiari type I malformation with syringosubarachnoid-peritoneal shunt. J Korean Neurosurg Soc. 2015. 57: 311-3

3. Arnautovic A, Pojskić M, Arnautović KI. Adult Chiari malformation type I: Surgical anatomy, microsurgical technique, and patient outcomes. Neurosurg Clin N Am. 2023. 34: 91-104

4. Ball MJ, Dayan AD. Pathogenesis of syringomyelia. Lancet. 1972. 2: 799-801

5. Bateman GA, Bateman AR. Syringomyelia is associated with a reduction in spinal canal compliance, venous outflow dilatation and glymphatic fluid obstruction. J Clin Med. 2023. 12: 6646

6. Batzdorf U, McArthur DL, Bentson JR. Surgical treatment of Chiari malformation with and without syringomyelia: Experience with 177 adult patients: Clinical article. J Neurosurg. 2013. 118: 232-42

7. Bhimani AD, Esfahani DR, Denyer S, Chiu RG, Rosenberg D, Barks AL. Adult Chiari I malformations: An analysis of surgical risk factors and complications using an international database. World Neurosurg. 2018. 115: e490-500

8. Chang TW, Zhang X, Maoliti W, Yuan Q, Yang XP, Wang JC. Outcomes of dura splitting decompression versus posterior fossa decompression with duraplasty in the treatment of Chiari I malformation: A systematic review and meta-analysis. World Neurosurg. 2021. 147: 105-14

9. Chiari H. Concerning alterations in the cerebellum resulting from cerebral hydrocephalus 1891. Pediatr Neurosci. 1987. 13: 3-8

10. Chotai S, Kshettry VR, Lamki T, Ammirati M. Surgical outcomes using wide suboccipital decompression for adult Chiari I malformation with and without syringomyelia. Clin Neurol Neurosurg. 2014. 120: 129-35

11. Dlouhy BJ, Dawson JD, Menezes AH. Intradural pathology and pathophysiology associated with Chiari I malformation in children and adults with and without syringomyelia. J Neurosurg Pediatr. 2017. 20: 526-41

12. Duddy JC, Allcutt D, Crimmins D, O’Brien D, O’Brien DF, Rawluk D. Foramen magnum decompression for Chiari I malformation: A procedure not to be underestimated. Br J Neurosurg. 2014. 28: 330-4

13. Durham SR, Fjeld-Olenec K. Comparison of posterior fossa decompression with and without duraplasty for the surgical treatment of Chiari malformation Type I in pediatric patients: A meta-analysis. J Neurosurg Pediatr. 2008. 2: 42-9

14. Eide PK, Lundar T. Arne Torkildsen and the ventriculocisternal shunt: The first clinically successful shunt for hydrocephalus. J Neurosurg. 2016. 124: 1421-8

15. Erdogan E, Cansever T, Secer HI, Temiz C, Sirin S, Kabatas S. The evaluation of surgical treatment options in the Chiari Malformation Type I. Turk Neurosurg. 2010. 20: 303-13

16. Frassanito P, Tamburrini G, Di Rocco C, editors. Surgical treatment of hydrocephalus based on CSF shunt devices. Textbook of pediatric neurosurgery. Berlin, Germany: Springer; 2020. p. 567-74

17. Frič R, Eide PK. Perioperative monitoring of pulsatile and static intracranial pressure in patients with Chiari malformation type 1 undergoing foramen magnum decompression. Acta Neurochir (Wien). 2016. 158: 341-7

18. Fuentes AM, Chiu RG, Nie J, Mehta AI. Inpatient outcomes of posterior fossa decompression with or without duraplasty for Chiari malformation type I. Clin Neurol Neurosurg. 2021. 207: 106757

19. Gardner WJ, Abdullah AF, Mccormack LJ. The varying expressions of embryonal atresia of the fourth ventricle in adults: Arnold-Chiari malformation, Dandy-Walker syndrome, arachnoid cyst of the cerebellum, and syringomyelia. J Neurosurg. 1957. 14: 591-605

20. Gardner WJ, Angel J. The cause of syringomyelia and its surgical treatment. Cleve Clin Q. 1958. 25: 4-8

21. Gardner WJ, Goodall RJ. The surgical treatment of Arnold-Chiari malformation in adults; an explanation of its mechanism and importance of encephalography in diagnosis. J Neurosurg. 1950. 7: 199-206

22. Giannakaki V, Wildman J, Thejasvin K, Pexas G, Nissen J, Ross N. Foramen magnum decompression for chiari malformation type 1: Is there a superior surgical technique?. World Neurosurg. 2023. 170: e784-90

23. Goel A, Vutha R, Shah A, Ranjan S, Jadhav N, Jadhav D. Atlantoaxial fixation for failed foramen magnum decompression in patients with Chiari formation. J Craniovertebr Junction Spine. 2020. 11: 186-92

24. Goel A. Is atlantoaxial instability the cause of Chiari malformation? Outcome analysis of 65 patients treated by atlantoaxial fixation. J Neurosurg Spine. 2015. 22: 116-27

25. Guan J, Yuan C, Zhang C, Ma L, Yao Q, Cheng L. Intradural pathology causing cerebrospinal fluid obstruction in syringomyelia and effectiveness of foramen magnum and foramen of magendie dredging treatment. World Neurosurg. 2020. 144: e178-88

26. Guyotat J, Bret P, Jouanneau E, Ricci AC, Lapras C. Syringomyelia associated with type I Chiari malformation. A 21-year retrospective study on 75 cases treated by foramen magnum decompression with a special emphasis on the value of tonsils resection. Acta Neurochir (Wien). 1998. 140: 745-54

27. Gürbüz MS, Berkman MZ, Ünal E, Akpınar E, Gök Ş, Orakdöğen M. Foramen magnum decompression and duraplasty is superior to only foramen magnum decompression in chiari malformation type 1 associated with syringomyelia in adults. Asian Spine J. 2015. 9: 721-7

28. Han RK, Medina MP, Giantini-Larsen AM, Chae JK, Cruz A, Garton ALA. Fourth ventricular subarachnoid stent for Chiari malformation type I-associated persistent syringomyelia. Neurosurg Focus. 2023. 54: E10

29. Heiss JD, Snyder K, Peterson MM, Patronas NJ, Butman JA, Smith RK. Pathophysiology of primary spinal syringomyelia. J Neurosurg Spine. 2012. 17: 367-80

30. Klekamp J. Surgical treatment of Chiari I malformation--analysis of intraoperative findings, complications, and outcome for 371 foramen magnum decompressions. Neurosurgery. 2012. 71: 365-80

31. Knafo S, Malcoci M, Morar S, Parker F, Aghakhani N. Surgical management after Chiari decompression failure: Craniovertebral junction revision versus shunting strategies. J Clin Med. 2022. 11: 3334

32. Krishna V, McLawhorn M, Kosnik-Infinger L, Patel S. High long-term symptomatic recurrence rates after Chiari-1 decompression without dural opening: A single center experience. Clin Neurol Neurosurg. 2014. 118: 53-8

33. Kumar A, Pruthi N, Devi BI, Gupta AK. Response of syrinx associated with Chiari I malformation to posterior fossa decompression with or without duraplasty and correlation with functional outcome: A prospective study of 22 patients. J Neurosci Rural Pract. 2018. 9: 587-92

34. Langridge B, Phillips E, Choi D. Chiari malformation type 1: A systematic review of natural history and conservative management. World Neurosurg. 2017. 104: 213-9

35. Lin W, Duan G, Xie J, Shao J, Wang Z, Jiao B. Comparison of results between posterior fossa decompression with and without duraplasty for the surgical treatment of chiari malformation type I: A systematic review and meta-analysis. World Neurosurg. 2018. 110: 460-74.e5

36. Logue V, Edwards MR. Syringomyelia and its surgical treatment--an analysis of 75 patients. J Neurol Neurosurg Psychiatry. 1981. 44: 273-84

37. Mandel M, Ferreira da Silva IA, Paiva W, Li Y, Steinberg GK, Teixeira MJ. Minimally invasive foramen magnum durectomy and obexostomy for treatment of craniocervical junction-related syringomyelia in adults: Case series and midterm follow-up. J Neurosurg Spine. 2020. 33: 148-57

38. Mazerand E, Benichi S, Taverne M, Paternoster G, Rolland A, Antherieu P. Chiari malformation type I surgery in children: French multicenter 10-year cohort. J Neurosurg Pediatr. 2022. 30: 210-6

39. Morota N, Ihara S, Araki T. Torkildsen shunt: Re-evaluation of the historical procedure. Childs Nerv Syst. 2010. 26: 1705-10

40. Mutchnick IS, Janjua RM, Moeller K, Moriarty TM. Decompression of Chiari malformation with and without duraplasty: Morbidity versus recurrence. J Neurosurg Pediatr. 2010. 5: 474-8

41. Ohnishi Y, Fujiwara S, Takenaka T, Kawamoto S, Iwatsuki K, Kishima H. An increase in the posterior subarachnoid space accelerates the timing of syrinx resolution after foramen magnum decompression of type I Chiari malformation. Sci Rep. 2021. 11: 19152

42. Osborne-Grinter M, Arora M, Kaliaperumal C, Gallo P. Posterior fossa decompression and duraplasty with and without arachnoid preservation for the treatment of adult Chiari malformation type 1: A systematic review and meta-analysis. World Neurosurg. 2021. 151: e579-98

43. Özlen F, Kucukyuruk B, Alizada O, Guler H, Akgun MY, Kafadar AM. Comparison of two surgical techniques in Chiari Malformation Type 1 patients: Duraplasty alone vs duraplasty with arachnoid dissection. Clin Neurol Neurosurg. 2021. 206: 106686

44. Perrini P, Anania Y, Cagnazzo F, Benedetto N, Morganti R, Di Carlo DT. Radiological outcome after surgical treatment of syringomyelia-Chiari I complex in adults: A systematic review and meta-analysis. Neurosurg Rev. 2021. 44: 177-87

45. Pillay PK, Awad IA, Hahn JF. Gardner’s hydrodynamic theory of syringomyelia revisited. Cleve Clin J Med. 1992. 59: 373-80

46. Riordan CP, Scott RM. Fourth ventricle stent placement for treatment of recurrent syringomyelia in patients with type I Chiari malformations. J Neurosurg Pediatr. 2019. 23: 164-70

47. Rizk EB, editors. Syringomyelia; An update on clinicopathological studies, diagnosis, and management. Cerebrospinal fluid and subarachnoid space. Netherlands: Elsevier; 2023. p. 7-30

48. Sacco D, Scott RM. Reoperation for Chiari malformations. Pediatr Neurosurg. 2003. 39: 171-8

49. Schuster JM, Zhang F, Norvell DC, Hermsmeyer JT. Persistent/Recurrent syringomyelia after Chiari decompression-natural history and management strategies: A systematic review. Evid Based Spine Care J. 2013. 4: 116-25

50. Siasios J, Kapsalaki EZ, Fountas KN. Surgical management of patients with Chiari I malformation. Int J Pediatr. 2012. 2012: 640127

51. Sun P, Zhou M, Liu Y, Du J, Zeng G. Fourth ventricle stent placement for treatment of type I Chiari malformation in children. Childs Nerv Syst. 2023. 39: 671-6

52. Venanzi MS, Pavanello M, Pacetti M, Secci F, Rossi A, Consales A. Surgical management of Chiari malformation Type I in the pediatric population: A single-center experience. J Clin Med. 2024. 13: 3430

53. Wang B, Wang C, Zhang YW, Liang YC, Liu WH, Yang J. Long-term outcomes of foramen magnum decompression with duraplasty for Chiari malformation type I in adults: A series of 297 patients. Neurosurg Focus. 2023. 54: E5

54. Williams B. Simultaneous cerebral and spinal fluid pressure recordings 2 Cerebrospinal dissociation with lesions at the foramen magnum. Acta Neurochir (Wien). 1981. 59: 123-42

55. Zakaria R, Kandasamy J, Khan Y, Jenkinson MD, Hall SR, Brodbelt A. Raised intracranial pressure and hydrocephalus following hindbrain decompression for Chiari I malformation: A case series and review of the literature. Br J Neurosurg. 2012. 26: 476-81

56. Zhao JL, Li MH, Wang CL, Meng W. A Systematic review of Chiari I malformation: Techniques and outcomes. World Neurosurg. 2016. 88: 7-14