Abstract
Chiari malformation type I (CM-I) is the most common subtype of Chiari malformation which can lead to brainstem compression and alterations in cerebrospinal fluid (CSF) flow. Common complications in patients undergoing traditional surgical approach include pseudomeningocele, CSF leak, and exacerbation of symptoms. The authors present a new minimally invasive surgery technique for protection and strengthening of the myodural bridge (MDB) in order to prevent the postoperative complications. A retrospective study was performed on 55 CM-I patients undergoing surgical treatment from January 2019 to April 2024 in a center. These patients underwent the surgical procedure of either posterior fossa decompression with duraplasty and tonsillar coagulation (PFDDC) or PFDDC with protection and strengthening of the MDB (PFDDC + MDB). The clinical outcomes and complications of the two procedures. 29 patients underwent PFDDC, and 26 patients underwent PFDDC + MDB. Overall complications rates were significantly reduced in the PFDDC + MDB group (3.8% vs. 34.5%, P = 0.012). Meningitis was observed in 3 (10.3%) in the PFDDC group and 1 (3.8%) in the PFDDC + MDB group (P = 0.613). Pseudomeningocele was more frequent in the PFDDC group than in the PFDDC + MDB group (24.1% vs. 0%, P = 0.011). No patient required a revision operation. There were no statistical differences in symptom improvement between the two groups. PFDDC + MDB seems to be a safe and effective treatment for CM-I patients with or without syringomyelia. This new procedure can bring clinical improvement and lower complication rates.
Supplementary Information
The online version contains supplementary material available at 10.1038/s41598-025-92506-7.
Keywords: Chiari malformation type I, Complications, Myodural Bridge, Surgery
Subject terms: Anatomy, Neurology
Introduction
Chiari Malformation encompasses a group of neurological disorders characterized by structural abnormalities in the posterior fossa. The classification and definition of Chiari Malformation have evolved over time, and there are different subtypes of Chiari Malformation based on the specific anatomical features and associated abnormalities1. Chiari I Malformation (CM-I) is the most common subtype of Chiari Malformation characterized by the descent of the cerebellar tonsils below the foramen magnum, leading to brainstem compression and alterations in CSF flow, and potential complications such as suboccipital headache and syringomyelia2. Patients with progressively worsening symptoms or CM-I with enlarged syringomyelia usually require surgery. One common surgical approach for CM-I is posterior fossa decompression (PFD), which has been shown to be effective in treating CM-I3. However, complications such as pseudomeningocele (PMC), cerebrospinal fluid (CSF) leak, and exacerbation of symptoms or recurrence of syringomyelia requiring revision surgery are not uncommon4–7. The methods for reducing CSF leak and chronic headache after surgery are still unclear.
The suboccipital region is one of the most complex parts of the human body. It was reported that a group of dense connective fibers, named as the “myodural bridge (MDB)”, originated from the suboccipital muscles (rectus capitis posterior minor (RCPmi), rectus capitis posterior major (RCPma), and obliquus capitis inferior (OCI)) and inserted to the cervical spinal dura mater (SDM), through the posterior atlanto-axial and atlanto-occipital interspaces8–14 (Fig. 1).
Fig. 1.
Schematic presentation of the myodural bridge complex. Posterolateral illustration of the craniocervical junction. The myodural bridges are seen connecting the cervical spinal dura mater to the suboccipital muscles (red arrow). OCCI: occipital bone; C1, atlas; C2, axis; RCPmi, rectus capitis posterior minor; RCPma, rectus capitis posterior major; OCI, obliquus capitis inferior; SDM, spinal dura mater.
Regarding the functions of the MDB, it is believed by some scholars that the MDB might resist the cervical SDM infolding during head movement and serve as a proprioceptor in preventing excessive head flexion/extension15,16. In recent years, the MDB is also considered to be one of the power sources for CSF circulation17–20. Additionally, morphological studies on MDB found that the MDB contributes to the formation of the SDM21–23. Zhuang et al. found that the cerebral dura mater, the periosteum located at the brim of the foramen magnum, and the MDB composed the posterior wall of the SDM in the P45 plastinated slices23. They proposed that the three sources of fibers should be protected during cervical surgeries to prevent dura damage.
It is worth noting that the MDB has always been neglected in various PFD procedures for CM-I surgery in the past, and its damage could be one of the main causes of postoperative CSF leak and headache24,25. Therefore, we established an MDB-protecting concept and sought a novel surgical approach to preserve the structures and functions of the MDB. The aim of this study was to analyze the outcome of a less invasive PFD using an MDB-protecting technique in CM-I.
Methods
Patients and data collection
Between January 2019 and April 2024, 55 patients with symptomatic CM-I underwent surgical treatment by the same surgeon at our hospital. Posterior fossa decompression with duraplasty and tonsillar coagulation (PFDDC) was performed in 29 patients, while 26 patients underwent PFDDC with protection and strengthening of the MDB (PFDDC + MDB). The diagnosis of CM-I was confirmed by MRI. Patients with other types of Chiari Malformation, acquired CM-I following normal or high-pressure hydrocephalus, previous spinal surgery, and craniovertebral instability requiring fusion at the time of decompression were excluded.
Relevant clinical parameters, such as age, gender, symptoms, neurologic deficits, complications, duration of operation and hospitalization, and preoperative and postoperative radiological characteristics were recorded. PMC was identified on follow-up MRI as a hyperintense fluid collection in the extradural space on sagittal T2-weighted imaging7. Postoperative outcomes in the two groups were evaluated by the following indicators: (1) The visual analog scale (VAS) for headache intensity, (2) Neck Disability Index (NDI) for neck pain-related disability, (3) the modified Japanese Orthopedic Association (mJOA) scores for neurological function, (4) Chicago Chiari Outcome Scale (CCOS) for comprehensive outcome evaluation of pain symptoms, functionality, and complications, and (5) Vaquero Index (VI) for assessing the size of syringomyelia26,27. Duration of operation and hospitalization were collected. All patients were followed up at 3 months after surgery. The retrospective study was approved by the Ethics Committee for Clinical Research in Shenyang General Hospital of Northern Theater Command (Date: 20.06.2023, Decision No: Y2023117). All methods were carried out in accordance with relevant guidelines and regulations. The informed consent was waived by the Ethics Committee for Clinical Research in Shenyang General Hospital of Northern Theater Command, as the data for this study was taken from a hospital data which is not publicly available. Patient confidentiality was protected by anonymizing all records prior to analysis. Identifiable information was replaced with unique codes, and the master list linking these codes to patient identities was securely stored with restricted access. Only authorized researchers involved in the study had access to the data, and all team members signed confidentiality agreements.
Surgical procedures
PFDDC was conducted between January 2019 and May 2022. Since June 2022, guided by the new theory of the function of the MDB, the main surgeon has decided to adopt PFDDC + MDB for all CM-I patients to avoid potential complications. Surgeries were performed in the prone position with the three-point pin head fixation, and the neck was placed in slight flexion. A 5 to 6 cm midline skin incision extending from the inion to the atlas (C1) was made in the atlanto-occipital region to expose the foramen magnum.
In the PFDDC group (Fig. 2a), a standard subperiosteal dissection of muscle from the inferior aspect of the occipital bone and the arch of the C1 was performed, followed with a 25–30 mm suboccipital craniectomy and C1 laminectomy. The posterior atlanto-occipital membrane was removed, and the dura was incised under a microscope in a Y-shaped fashion.
Fig. 2.
Simplified representation of surgical techniques for Chiari Malformation Type I. (a) Posterior fossa decompression with duraplasty and tonsillar coagulation (PFDDC). (b and c) PFDDC with protection and strengthening of the myodural bridge (PFDDC+MDB). (b) Suboccipital craniectomy and protection of the MDB. (c) Intradural decompression and strengthening of the MDB at the lower edge of the incision. OCCI: occipital bone; C1, atlas; C2, axis; RCPmi, rectus capitis posterior minor; RCPma, rectus capitis posterior major; OCS, obliquus capitis superior; OCI, obliquus capitis inferior; red arrow, MDB; green asterisk, posterior atlanto-occipital membrane; blue asterisk, synthetic dural substitute; yellow arrow, suture point of the RCPmi and the dura at the lower edge of the incision.
The patients in the PFDDC + MDB group (Figs. 2b-c and 3) were characterized by effective protection and strengthening of the MDB. The attachment of the RCPmi on the occipital bone and the C1 was preserved. The arch of the C1, the posterior atlanto-occipital membrane (PAOM), and the MDB fibers were maximally preserved. The incision on the PAOM and the dura at the atlanto-occipital gap was strictly made along the midline. Furthermore, the dura at the lower edge of the incision was sutured with the RCPmi on both sides to strengthen the MDB and increase visual exposure.
Fig. 3.
View of the posterior occipito-cervical junction during posterior fossa decompression with duraplasty and tonsillar coagulation, with protection and strengthening of the myodural bridge (PFDDC+MDB). (a) After retracting the suboccipital muscles bilaterally, the occipital bone (triangle) and foramen magnum were exposed without removing the posterior arch of the atlas (blue arrow) and the attachment of the rectus capitis posterior minor (RCPmi). The MDB (green asterisk) was clearly visualized. (b and c) After a 25–30 mm suboccipital craniectomy, an incision was made strictly on the posterior atlanto-occipital membrane and the dura at the atlanto-occipital gap along the midline, then extended to form a Y shape. The MDB fibers were preserved at the same time. The dura at the lower edge of the incision was sutured with the RCPmi to strengthen the MDB (yellow arrow). The underlying arachnoid and the tonsils (red asterisk) could be seen. (d and e) After exploring the foramen of Magendie, tonsil coagulation or subpial resection was performed. (f) The duraplasty was performed with synthetic dural substitute (blue asterisk) and watertight sutures.
The intradural surgical procedures were same in both groups. After opening of the dura, the foramen of Magendie was explored, and any adhesions found were dissected. Tonsil coagulation or subpial resection was performed to the lowermost end of the tonsil. In the PFDDC + MDB group, the surgical field was relatively small, especially in cases with herniation of cerebellar tonsils below the posterior arch of the C1. This could be improved by adjusting microscope angle and performing gradual tonsil coagulation and subpial resection. After completing the duraplasty using synthetic dural substitute with No. 5 − 0 Prolene suture and reinforcement with fibrin sealant (Porcine Fibrin Sealant Kit, Bioseal Biotech, China), the outer layers were carefully sutured step-by-step. Patients were transferred to the neuro intensive care unit postoperatively.
Statistical analysis
All statistical analyses were performed using R software (version 4.2.2). Independent samples t-test and Wilcoxon rank-sum test were utilized for the continuous variables. For the categorical variables, comparisons between groups were performed using Chi-squared test. For indices measured both preoperatively and three months postoperatively, including VAS, NDI, mJOA score, and VI, an analysis of covariance (ANCOVA) was applied. A P value < 0.05 was considered significant. To validate the adequacy of the sample size, a post-hoc power analysis was conducted using G*Power software (version 3.1.9.7). A two-tailed z-test was performed with a significance level of 0.05. The total sample size of 55 cases provided an achieved power of 80.3% in estimating the rate of complication based on the observed rate in this cohort.
Results
Patients
A total of 55 patients satisfied the inclusion and exclusion criteria, and all completed pre- and post- operative assessment. Table 1 represents the baseline demographic and clinical features. The mean age of patients was 49.8 years (SD: 12.4 years), and 39 (70.9%) were female. Syringomyelia was present in 44 (80.0%) of them. 29 patients underwent PFDDC, and 26 patients underwent PFDDC + MDB. There were no statistically significant differences in age (P = 0.193), gender distribution (P = 0.795) and diagnosis distribution (P = 0.589) between the two groups. The most common symptoms were numbness in extremities (61.8%), frequently with motor weakness (49.1%), then suboccipital headache (43.6%) and Sensory deficits (43.6%). Among all the symptoms, only lower cranial nerve palsies showed a significant difference between the two groups (P = 0.036). The mean tonsillar descent was 9.0 mm (IQR: 7.0–12.5 mm) overall, but PFDDC + MDB group had a higher mean tonsillar descent (P = 0.045). Duration of the operation and hospitalization are shown in Table 2.
Table 1.
Baseline demographic and clinical features of the participants.
| Characteristic | Surgical regimen | P-value | ||
|---|---|---|---|---|
| Overall, N = 55 | PFDDC, N = 29 | PFDDC + MDB, N = 26 | ||
| Age (years) | 0.193 | |||
| Mean (SD) | 49.8 (12.4) | 47.7 (12.1) | 52.1 (12.3) | |
| Sex | 0.795 | |||
| Female, n (%) | 39 (70.9%) | 21 (72.4%) | 18 (69.2%) | |
| Male, n (%) | 16 (29.1%) | 8 (27.6%) | 8 (30.8%) | |
| Symptoms and Signs | ||||
| Sensory deficits, n (%) | 24 (43.6%) | 10 (34.5%) | 14 (53.8%) | 0.148 |
| Gait ataxia, n (%) | 15 (27.3%) | 4 (13.8%) | 11 (42.3%) | 0.018 |
| Numbness in extremities, n (%) | 34 (61.8%) | 20 (69.0%) | 14 (53.8%) | 0.249 |
| Suboccipital headache, n (%) | 24 (43.6%) | 14 (48.3%) | 9 (34.6%) | 0.201 |
| Neuropathic pain, n (%) | 13 (23.6%) | 9 (31.0%) | 4 (15.4%) | 0.173 |
| Motor weakness, n (%) | 27 (49.1%) | 11 (37.9%) | 16 (61.5%) | 0.080 |
| Apnea, n (%) | 7 (12.7%) | 4 (13.8%) | 3 (11.6%) | > 0.999 |
| Vertigo, n (%) | 7 (12.7%) | 2 (6.9%) | 5 (19.2%) | 0.236 |
| LCN palsies, n (%) | 11 (20.0%) | 3 (10.3%) | 8 (30.8%) | 0.059 |
| Cervical pain, n (%) | 12 (21.8%) | 4 (13.8%) | 7 (26.9%) | 0.385 |
| Spasticity, n (%) | 3 (5.5%) | 1 (3.4%) | 2 (7.7%) | 0.598 |
| Muscle atrophy, n (%) | 8 (14.5%) | 1 (3.4%) | 6 (23.1%) | 0.131 |
| Diagnosis | 0.589 | |||
| CM-I, n (%) | 11 (20.0%) | 5 (17.2%) | 6 (23.1%) | |
| CM-I /Syr, n (%) | 44 (80.0%) | 24 (82.8%) | 20 (76.9%) | |
| Tonsillar descent (mm) | 0.045 | |||
| Median (IQR) | 9.0 (7.0, 12.5) | 8.0 (6.2, 9.5) | 10.7 (7.9, 14.2) | |
| Comorbidity | ||||
| Ventriculomegaly, n (%) | 4 (7.3%) | 4 (13.8%) | 0 (0%) | 0.113 |
| Scoliosis, n (%) | 4 (7.3%) | 2 (6.9%) | 2 (7.7%) | > 0.999 |
| Arachnoid cyst, n (%) | 2 (3.6%) | 1 (3.4%) | 1 (3.8%) | > 0.999 |
PFDDC, posterior fossa decompression with duraplasty and tonsillar coagulation; PFDDC + MDB, PFDDC with protection and strengthening of the myodural bridge; LCN, lower cranial nerve; CM-I, Chiari Malformation type I; Syr, syringomyelia; IQR, interquartile range, SD, standard deviation.
Table 2.
Profile of Surgery-related parameters: duration and hospitalization analysis.
| Characteristic | Surgical regimen | P-value | ||
|---|---|---|---|---|
| Overall, N = 55 | PFDDC, N = 29 | PFDDC + MDB, N = 26 | ||
| Duration of the Operation (min) | 0.413 | |||
| Median (IQR) | 182.0 (159.0, 205.0) | 182.0 (163.5, 221.0) | 182.5 (153.5, 200.0) | |
| Duration of Hospitalization (days) | 0.356 | |||
| Median (IQR) | 16.0 (15.0, 20.0) | 16.0 (13.5, 20.5) | 17.0 (15.0, 20.5) | |
PFDDC, posterior fossa decompression with duraplasty and tonsillar coagulation; PFDDC + MDB, PFDDC with protection and strengthening of the myodural bridge; IQR, interquartile range.
Complications
With regard to postoperative complications (Table 3), overall complications were significantly reduced in the PFDDC + MDB compared with that in the PFDDC group (3.8% vs. 34.5%, P = 0.012). Meningitis was observed in 4 (7.3%) of the overall cohort, with 3 (10.3%) in the PFDDC group and 1 (3.8%) in the PFDDC + MDB group (P = 0.613). PMC was more frequent in the PFDDC (24.1%) than in the PFDDC + MDB (0%) group (P = 0.011).
Table 3.
Clinical outcome and complications comparing treatment groups.
| Characteristic | Surgical regimen | P-value | ||
|---|---|---|---|---|
| Overall, N = 55 | PFDDC, N = 29 | PFDDC + MDB, N = 26 | ||
| Follow-up (mos) | 0.072 | |||
| Median (IQR) | 4.00 (3.00, 6.00) | 5.00 (3.00, 8.50) | 3.00 (3.00, 5.00) | |
| Postop CCOS | 0.950 | |||
| Median (IQR) | 14.00 (13.00, 15.00) | 14.00 (13.00, 15.00) | 14.00 (13.00, 14.75) | |
| Complications | ||||
| Meningitis, n (%) | 4 (7.3%) | 3 (10.3%) | 1 (3.8%) | 0.613 |
| Pseudomeningocele, n (%) | 7 (12.7%) | 7 (24.1%) | 0(0%) | 0.011 |
| Total, n (%) | 11 (20.0%) | 10 (34.5%) | 1 (3.8%) | 0.012 |
PFDDC, posterior fossa decompression with duraplasty and tonsillar coagulation; PFDDC + MDB, PFDDC with protection and strengthening of the myodural bridge; CCOS, Chicago Chiari Outcome Scale; IQR, interquartile range.
Clinical outcome
The median follow-up time for all patients was 4.00 months (IQR: 3.00–6.00). The PFDDC group had a median follow-up of 5.00 months (IQR: 3.00–8.50), and the PFDDC + MDB group had a median follow-up of 3.00 months (IQR: 3.00–5.00) (P = 0.072). The median postoperative CCOS score was identical across the entire cohort and the individual groups, standing at 14.00 (IQR: 13.00–15.00) without any statistically significant difference between two groups (P = 0.950) (Table 3). At 3months follow-up, patients showed improvements of different symptoms in the neurological scores, including VAS for headache, NDI, mJOA scores, and VI. Figure 4 demonstrates pre- and post- operative imaging of one case who underwent PFDDC + MDB. However, there were no significant betweengroup differences (Table 4).
Fig. 4.
Pre- (a) and post-operative (b) T2-weighted sagittal MRI of the occipito-cervical junction in a 65-year-old male who underwent posterior fossa decompression with duraplasty and tonsillar coagulation, with protection and strengthening of the myodural bridge (PFDDC+MDB) for pain and weakness in left upper limb. The MRI images revealed an obvious decrease in syrinx size. Postoperative 3D reconstruction CT (c) showed the adequate decompression range of posterior cranial fossa and the preservation of the posterior arch of the atlas.
Table 4.
Neurological scores at 3 months comparing treatment groups.
| Change from baseline | Mean difference (95% CI) | P-value | ||
|---|---|---|---|---|
| PFDDC, N = 29 | PFDDC + MDB, N = 26 | |||
| VAS for headache | −19.52 (−21.88, −17.15) | −16.85 (−19.36, −14.34) | 2.67 (−0.78, 6.12) | 0.136 |
| Neck Disability Index | −0.11 (−1.32, 1.10) | 0.86 (−0.42, 2.14) | 0.97 (−0.76, 2.70) | 0.278 |
| mJOA score | 0.73 (0.48, 0.97) | 0.61 (0.36, 0.87) | −0.11 (−0.47, 0.25) | 0.546 |
| Vaquero index | −0.15 (−0.20, −0.10) | −0.11 (−0.16, −0.06) | 0.04 (−0.03, 0.11) | 0.273 |
Based on an ANCOVA model after adjusting P value. PFDDC, posterior fossa decompression with duraplasty and tonsillar coagulation; PFDDC + MDB, PFDDC with protection and strengthening of the myodural bridge; ANCOVA, Analysis of Covariance; CI, Confidence Interval; VAS, Visual Analog Scale; mJOA, modified Japanese Orthopedic Association.
Discussion
This study described a novel surgical approach (PFDDC + MDB) for CM-I, and showed the early outcome of a retrospective cohort study comparing PFDDC + MDB with regular PFDDC surgery. This new procedure significantly reduced the postoperative complications. All patients in the PFDDC + MDB group achieved good outcome in short-term follow-up, and no patient experienced CSF leak, PMC or revision surgery.
CSF-related events constitute the most common complications in patients undergoing posterior fossa decompression with duraplasty for CM-I28–31. Several factors contribute to the occurrence of PMC and CSF leak after CM-I surgery7,32. The choice of graft material for duraplasty, the technique used for dural closure and the skill of the surgeon could influence the risk of complications32,33. These complications can lead to symptoms such as persistent headache, neck pain, or the recurrence of neurological symptoms33. The most common complications observed in our study among the PFDDC group were PMC (24.1%) and meningitis (10.3%). The rate of PMC can vary greatly in different studies, which is probably due to its definition7,33,34. PMCs were classified as symptomatic complications requiring surgical intervention in early studies, while recent studies defined it as the radiological findings of abnormal CSF collection visible on MRI, which led to a higher incidence of PMC in patients receiving PFD. It shows that PMC is relatively common in radiological evaluation, although its clinical significance is uncertain. However, PMC and CSF leak did not happen in surgery with MDB preserving technique. MDB fibers originated from the suboccipital muscles pass through the posterior atlanto-axial and atlanto-occipital interspaces and merge into the SDM21. The MDB, the periosteum located at the brim of the foramen magnum and the cerebral dura mater contribute to the formation of the cervical SDM23. In our opinion, direct connections between MDB, PAOM, and SDM will structurally aid in force transmission. Traditional PFD procedures often lead to MDB damage and impair its ability to relieve tensile stress concentration on the dura, which result in PMC or CSF leak after surgery. Moreover, removing the posterior arch of the C1 and the attachment of RCPmi on the C1 can expand the volume of the postoperative epidural space, increasing the risk of PMC. Thus, meticulous surgical approach for MDB preservation is required so as to avoid CSF leak.
Headache is a common symptom experienced by individuals with CM-I both before and after PFD35,36. The exact underlying mechanism is unclear, but it is believed to be related to the obstruction of CSF flow and increased intracranial pressure35. After PFD, headaches may persist or even worsen in some patients. Dyste et al. reported that 20% of patients remained asymptomatic after PFD, while 66% experienced improvement in their symptoms36. One common reason for postoperative headache in CM-I patients is the presence of residual tonsillar herniation or inadequate decompression of the posterior fossa37. On the other hand, previous research considered that the MDB was an important driving force for CSF circulation and was correlated with chronic cervical headaches17–20. We believe that MDB dysfunction is one of the causes of headache in CM-I patients.
In order to reduce the incidence of CSF-related events caused by traditional PFD procedures, we propose a novel surgical approach. Protection and strengthening of the MDB protection are carried out with regular PFDDC in the study. Key techniques for protection and strengthening of the MDB include (1) preserving the origin and insertion points of the RCPmi and the posterior arch of C1, (2) protecting the PAOM and the MDB fibers, (3) midline incision of the PAOM and the dura at the atlanto-occipital gap, and (4) suturing the dura at the lower edge of the incision with the RCPmi. Overall complication rates of the PFDDC + MDB group significantly decreased compared with that of the PFDDC group (3.8% vs. 34.5%, P = 0.012). Notably, there was no CSF leak, PMC, or revision surgeries in patients underwent PFDDC + MDB. In addition, similar outcomes were presented in the two groups.
In this study, the MDB fibers can be identified and carefully protected under microscope to minimize the damage in patients underwent PFDDC + MDB. Due to the protection of the PAOM and the MDB, as well as strengthening of the MDB at the edge of the incision, CSF leak caused by high tension in the suture edges could be effectively avoided. Compared with the extradural decompression, PFDDC + MDB provided more sufficient decompression and no patients required a second operation38,39. Furthermore, syringomyelia reduction was observed in all patients after surgery in the PFDDC + MDB group. Techniques in the management of CSF obstruction and MDB preservation used in this study may help restore the normal flow of CSF and reduce the size of syrinx cavity. Abnormal development of the posterior fossa and downward movement of the cerebellar tonsils result in obstruction of CSF flow in the subarachnoid space at the foramen magnum, and a pressure differential ensues with fluid flowing from the fourth ventricle to the central canal, which may be the pathogenesis of syringomyelia40. Recent studies proposed that during head movement, the suboccipital muscles might pull the spinal dura capsule via the MDB producing changes in the volume and pressure of CSF at the occipito-cervical junction (OCJ), consequently promoting the circulation of the CSF11,17–19. Xu et al. noticed that the velocity and direction of CSF flow at the OCJ were significantly affected after head movements using the PC-MRI17,18. Moreover, the new approach minimized the extent of the procedure and reduced the volume of the postoperative epidural space.
Generally, the present results showed that PFDDC + MDB was a useful surgical approach for CM-I with or without syringomyelia. Clinical improvement and lower rate of CSF leak could be achieved through protection and strengthening of the MDB. Preserving the roles of the MDB in CSF circulation and reducing the amount of suture edge tension, as well as providing adequate intradural decompression, might be the potential mechanism.
Moreover, a recent investigation described an enlarged subarachnoid space dorsal to both the medulla oblongata and the upper portion of the cervical spinal cord, spanning from the foramen magnum to the upper border of the axis41. Li et al. named this space as the “occipito-atlantal cistern (OAC)”. They supposed that the OAC and the cisterna magna may act as a buffer zone for CSF dynamics stability in both cranial cavity and spinal canal at the OCJ. The main pathological lesions and surgical area of CM-I occurred at the OAC. We considered that PFDDC + MDB provided a wide decompression space at the OCJ, composed of the OAC and the cisterna magna. Based on Bernoulli’s principle, the MDB promotes the CSF flow in the space and decreases pressure on the dura, which can reduce the occurrence of CSF leakage and chronic headache.
Currently, there is no generally accepted guideline for the surgical management of CM-I with or without syringomyelia. Surgeons utilize various techniques, such as suboccipital craniotomy combined with resection of the posterior arch of C1 and the atlanto-occipital ligament, outer dural splitting with preservation of the inner layer, expansile duraplasty with or without arachnoid opening, and intradural decompression with or without tonsillar reduction and obex exploration42. A new approach of atlantoaxial fixation has also been introduced to restore craniocervical stability in certain CM-I cases43. Each of these techniques has its advantages and limitations, leading to debates about the optimal surgical strategy. Intradural decompression can effectively relieve symptoms, but the incidence of CSF-related complications is relatively high44. Posterior fossa decompression without duraplasty is less invasive, but the risk of recurrence is higher due to epidural scarring or inadequate decompression45. The PFDDC + MDB approach emphasizes the protection of MDB, balancing the reduction of complications and obtaining sufficient decompression. It restores CSF circulation at the OCJ, reduces the amount of suture edge tension, and reduces the volume of the postoperative epidural space, providing a new option for CM-I with syringomyelia. Additionally, the principles of MDB protection described in this study may extend to other procedures at the OCJ, such as surgeries for basilar invagination or atlantoaxial instability. In these cases, the integrity of the dura mater and CSF dynamics also need to be carefully considered, which indicates that the concept of MDB protection can be more widely used.
This study also has some limitations. The small sample size limits the generalizability of the results. Therefore, a post-hoc power analysis was performed to confirm sufficient statistical power to detect significant differences in complication rates. As a single-center retrospective study, there are potential selection and reporting biases, particularly due to the shift in surgical technique during the study period. Patient selection and one experienced doctor may amplify the effectiveness of the new surgical procedure. To minimize the bias, the study included a diverse patient group, applied standardized surgical techniques, and employed validated outcome measures and statistical adjustments. In addition, the short follow-up period was limited, but the early postoperative outcomes showed the advantage of PFDDC + MDB and reported our preliminary achievements in CM-I surgery. Subsequent multicenter prospective studies with large sample size and longer follow-up periods are needed to validate these findings and evaluate long-term outcomes.
Conclusion
In the current retrospective study, we introduce a novel surgical approach for CM-I with or without syringomyelia. Given that traditional surgical methods can lead to complications such as CSF leak and postoperative headache due to MDB damage, PFDDC + MDB seems to be an effective treatment. This new procedure can bring clinical improvement and lower complication rates.
Electronic supplementary material
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Acknowledgements
The authors acknowledge Wei-kai Zhu and Song Tao for wonderful suggestions in designing the present study, and An-ying Wang for assistance in data collection.
Author contributions
Hong-Jin Sui, Sheng-Bo Yu, and Dong-Sheng Pan contributed to conceived and designed the experiments. Dong-Sheng Pan, Jin-Jiang Li, and Zhen Wang contributed to performing the experiments. Dong-Sheng Pan and Kai-Qi contributed to analyzing the data and the drafting of the manuscript. Hong-Jin Sui, Sheng-Bo Yu, and Xiao-Ying Yuan contributed to funding acquisition. Jian-Fei Zhang, Zheng Nan, and Xiao-Ying Yuan contributed to the critical revision of the manuscript. All authors reviewed the manuscript.
Funding
This study was supported by National Natural Science Foundation of China (NSFC 32100928 awarded to Xiao-Ying Yuan), Innovation Support Project for Science and Technology Talent of Dalian (2023RG003 awarded to Hong-Jin Sui) and Key R&D Project of Liaoning Province (2020JH/1050004 awarded to Sheng-Bo Yu).
Data availability
Data is provided within the manuscript.
Declarations
Competing interests
The authors declare no competing interests.
Ethics declarations
The informed consent was waived by the Ethics Committee for Clinical Research in Shenyang General Hospital of Northern Theater Command, as the data for this study was taken from a hospital data which is not publicly available.
Footnotes
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Dong-Sheng Pan and Kai-Qi Yang contributed equally to this work.
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