Chiari Malformation Type I and Syringomyelia: Outcomes of Arachnoid-Preserving Surgical Technique

Introduction

Chiari malformation type-I (CM-I) is a structural anomaly characterized by the downward herniation of the cerebellar tonsils through the foramen magnum [1]. This condition often leads to compression of the brainstem and cerebellum, manifesting in various neurological symptoms [2]. As a result of this, syringomyelia can develop. Syringomyelia, the formation of a fluid-filled cavity within the spinal cord, is a frequent complication associated with CM-I [3]. Chiari malformations have been classified into 4 types based on the type of herniation of brain tissue displaced into the spinal canal and the characteristics of brain or spinal developmental anomalies. This study aims to assess the treatment outcomes of CM-I [4].

The standard management of CM-I, particularly when accompanied by syringomyelia, typically involves surgical intervention. In some patient groups, particularly in those with less severe herniation or specific anatomical considerations, a less invasive approach involving only cranial decompression without dural opening has been suggested and shown to be effective [3]. However, for severe cases, the surgical procedure for this malformation is suboccipital decompression [5].

Three main surgical treatment methods have been defined: bone-only decompression, bone decompression with duraplasty, and bone decompression followed by dural opening and tonsillar resection with subsequent duraplasty. Other methods are essentially variations of these 3 techniques [4]. Traditional suboccipital decompression includes the removal of the bone at the back of the skull, resectioning the posterior arch of C1, and opening the dura [6]. However, this approach can disrupt the arachnoid membrane, potentially leading to complications, such as arachnoiditis and cerebrospinal fluid (CSF) leakage [7,8].

In response to these challenges, a modified surgical technique, known as the arachnoid-preserving suboccipital decompression, has been developed [9]. This technique aims to maintain the integrity of the arachnoid membrane while a duraplasty using graft material is performed, thereby reducing the likelihood of CSF leakage and other complications associated with traditional methods.

This studied included 89 patients who received a diagnosis of CM-I between 2016 and 2023. We present our experience with arachnoid-preserving suboccipital decompression in treating CM-I patients with syringomyelia. We focus on the clinical outcomes of this modified technique, including the incidence of postoperative complications, neurological improvement, and patient satisfaction. We subsequently compare these results with those reported for traditional suboccipital decompression. This study aims to assess the effectiveness and safety of the arachnoid-preserving suboccipital decompression in CM-I patients with syringomyelia, contributing to the growing body of evidence on surgical management strategies for this condition and potentially guiding future treatment decisions.

Material and Methods

ETHICS STATEMENT:

The Declaration of Helsinki 2013, ICJM recommendations, COPE’s International Standards for Editors and Authors, and other relevant bioethical guidelines were considered during the conduct of the study. The Health Sciences University received local ethics committee approval, numbered 03/2024-2426.

STUDY DESIGN:

This retrospective study was conducted at a tertiary referral center. The institutional review board provided the study’s approval, ensuring adherence to ethical standards. All patients provided informed consent for their inclusion in the study.

PATIENT POPULATION:

The study included 89 patients (14 to 61 years) who underwent arachnoid-preserving suboccipital decompression for CM-I with syringomyelia, and received a diagnosis of CM-I and syringomyelia via magnetic resonance imaging (MRI) between 2016 and 2023. Patients with a history of previous CM-I surgery or with a diagnosis of other neurological diseases were excluded. The minimum follow-up period postoperatively was set at 9 months.

DATA COLLECTION:

Data were collected from digital medical records, encompassing demographic information, clinical presentation, radiological findings, surgical details, postoperative complications, neurological outcomes, and patient satisfaction. Radiological evaluations included preoperative and postoperative MRI scans to assess the size and resolution of the syrinx. Clinical outcomes were assessed using the visual analog scale (VAS), which evaluates neurological symptoms such as headache, neck pain, numbness, and weakness.

SURGICAL TECHNIQUE:

All surgeries were performed by a single experienced neurosurgeon. A 6 to 7 cm-long skin incision was made, starting from the occipital protuberance and extending to the spinous process of C2. The subcutaneous tissue was passed, and the cervical fascia was exposed. The fascia, approximately 2×4 cm in oval shape, was harvested. Subsequently, the muscles were dissected along the midline. A craniotomy was performed, and with the help of a Kerrison Ronguer, a suboccipital craniectomy was started. Following this, a C1 laminectomy was performed. The dura was opened under the microscope, as shown in the drawings, with the arachnoid preserved in a linear manner. Duraplasty was then performed, using fascia. Afterward, Tissel was applied on top. The microscope stage was demonstrated in the video. In our cases, decompression sizes ranging from a minimum of 3×2.5 cm to a maximum of 3×3 cm were achieved.. However, in patients with extremely narrow posterior fossa, the vertical limit was calculated as 2.5 cm, so that the decompression did not extend to the transverse sinus. To prevent dead space formation and minimize tissue damage, muscle dissection was limited to bone decompression borders. Moreover, the C1 laminectomy was limited to 2 cm to the midline. The arachnoid-preserving suboccipital decompression technique involved a midline suboccipital craniectomy, followed by a dural incision with arachnoid preservation and duraplasty, using a muscle graft material. The dural incision was made linearly, differing from the current literature. The graft material used was autologous pericranium. Illustrative figures of the surgical technique (Figures 1, 2) and a surgical Video 1 are provided to demonstrate the procedure.

OUTCOME MEASURES:

The primary outcome measure was the incidence of postoperative complications, including CSF leakage, wound infection, and arachnoiditis. The secondary outcome measures included neurological improvement as assessed by the VAS scale and patient satisfaction with surgical outcomes. Preoperative and postoperative MRI scans in the third and ninth months were performed for assessment. Representative MRI images are shown in Figure 3.

STATISTICAL ANALYSIS:

Statistical analyses were performed using the MacCalc Statistical Package Program (version 20.009; Ostend, Belgium). Categorical data are defined as frequency and percent, while numerical data are presented as mean, standard deviation, median, minimum, and maximum. The chi-square test was used to compare categorical groups, and the Mann-Whitney U test was used for numerical data. The Kolmogorov-Smirnov test was used to determine the suitability of the groups for normal distribution. A significance level of P<0.05 was used.

Results

SEX, SYRINX PRESENCE, AND POSTOPERATIVE SYRINX EXISTENCE:

The patient cohort consisted predominantly of female patients, with 69 (77.5%) female and 20 (22.5%) male patients. Preoperatively, the presence of syrinx was found in 42 patients (47.2%), while 47 patients (52.8%) did not have a syrinx. Postoperatively, the syrinx disappeared in 7 patients (16.7%) and was minimal in 35 patients (83.3%), indicating a significant reduction in syrinx size following surgery (Table 1).

AGE DISTRIBUTION BY SEX:

The age range of the patients was between 14 and 61. The mean age for female patients was 39.1 years (SD=10.8), and for male patients, 36.7 years (SD=11.7). This difference in age distribution was not statistically significant (P=0.392), suggesting that age and sex did not markedly influence the outcomes of the surgical intervention (Table 2).

RELATION BETWEEN PREOPERATIVE VAS SCORE AND PATIENT SEX:

All 8 male patients with mild symptoms (VAS score 1–3) showed improvement in the preoperative phase. Among female patients, 34 (75.6%) had moderate symptoms (VAS score 4–6), and 27 (75%) had severe symptoms (VAS score 7–10). The correlation between preoperative VAS scores and patient sex was not statistically significant (P=0.279), indicating that sex did not significantly impact the severity of symptoms before surgery (Table 3).

PREOPERATIVE AND POSTOPERATIVE VAS SCORE RELATED TO SYRINX:

A syrinx was associated with higher preoperative VAS scores, indicating more severe symptoms. This difference was statistically significant (P<0.001). Postoperatively, both groups (with and without syrinx) showed significant improvement in VAS scores, suggesting reduced symptom severity. The presence of a syrinx did not correlate with postoperative VAS scores, age, ectopia, or hospitalization duration (Table 4).

We present a syrinx reduction in 83.3% of our cases and a total reduction (disappearance from all MRI sections) in 16.7%. Headache increasing with the valsalva maneuver showed regression in all patients. Non-valsalva headache frequency also decreased. Other non-valsalva headaches were directed to the Neurology Department for evaluation for headache syndromes.

The mean surgery duration was 90 min, and the mean hospitalization duration was 2.75 days.

These results demonstrate that the arachnoid-preserving suboccipital decompression technique effectively managed CM-I with syringomyelia by significantly improving symptoms and patient satisfaction. The technique showed its efficacy irrespective of the initial severity of the condition, sex, or age of the patients.

Discussion

The study included 89 patients, with 69 female (77.5%) and 20 male (22.5%) patients. A significant reduction in syrinx size was observed in 83.3% of patients, with complete resolution in 16.7%. The mean surgery duration was 90 min, and the average hospitalization duration was 2.75 days. All patients experienced significant improvements in neurological symptoms, such as headache, neck pain, numbness, and weakness. High levels of patient satisfaction were reported, with 100% of patients satisfied with their surgical outcomes. The incidence of complications, such as CSF leakage and arachnoiditis, was notably lower than that of traditional methods.

CM-I is a prevalent congenital condition in which the cerebellar tonsils herniate through the foramen magnum into the spinal canal, causing compression of the brainstem and spinal cord [1,2,3]. The primary treatment goal for CM-I is to alleviate this compression and improve or prevent the development of associated symptoms [10]. Treatment options are divided into conservative management, which includes medications for symptom management, and surgical intervention. However, conservative management alone is often insufficient in addressing the underlying anatomical abnormality [11].

Surgical intervention remains the mainstay of treatment for CM-I. The debate continues among experts regarding the optimal surgical approach. Options range from follow-up without surgical intervention to various degrees of bone decompression, with or without duraplasty, arachnoid dissection, tonsillar resection, and coagulation [12–17]. While bone decompression alone has shown unsatisfactory results, bone decompression with duraplasty generally yields more positive outcomes. However, adding tonsillar resection and coagulation to the surgical method has been associated with higher complication rates [13,14,16,17]. Conversely, some studies report better results with tonsillectomy [15], highlighting the need for more consensus on the best surgical management for patients with CM-I.

Evaluating clinical and radiological outcomes after surgery is challenging due to the variety of clinical signs, symptoms, and surgical techniques. Various outcome scores have been reported [18,19]; however, our study, similar to that of Kemerdere et al [9], did not use any scoring system. Instead, we based our findings on postoperative clinical and radiological follow-up results, showing 100% clinical improvement rates at first admission. All patients exhibited improved VAS scores; radiological improvement rates were also 100%.

Our study highlights the efficacy of the arachnoid-preserving suboccipital decompression technique. This approach aligns with the consensus that positive clinical and radiological results are higher in the duraplasty group than in the non-duraplasty group [9]. Notably, no significant difference in clinical results and syrinx reduction was observed between cases with arachnoid dissection and those with arachnoid preservation [20]. Our findings of high rates of clinical results and syrinx reduction with arachnoid-preserving duraplasty support this observation.

Complication rates related to surgical methods for CM-I vary widely, and are reported between 3% and 40% [8,9,21,22]. In the present study, we found that arachnoid-preserving techniques resulted in lower complication rates, particularly in avoiding CSF fistula and meningitis, which are more common in cases without duraplasty [23–25]. This supports the notion that preserving the arachnoid layer can reduce the incidence of symptomatic aseptic meningitis and CSF leakage.

Arachnoid-preserving suboccipital decompression is a modified surgical technique that aims to reduce the incidence of complications associated with traditional suboccipital decompression in the management of adult CM-I with syringomyelia [9]. Our study aimed to evaluate the clinical outcomes of this modified technique, including the incidence of postoperative complications, neurological improvement, and patient satisfaction. We found that the arachnoid-preserving suboccipital decompression technique was associated with a low incidence of postoperative complications. CSF fistula, meningitis, and arachnoiditis did not develop in any patients. Only 3 patients presented with superficial wound discharge, and these patients completely recovered with wound care and oral antibiotics in the early period, without the need of additional surgical intervention or hospitalization. These outcomes were associated with adipose tissue necrosis due to subcutaneous dissection during harvesting subcutaneous superficial fascia. However, this outcome is rarely encountered. Our findings show that the preservation of the arachnoid layer decreases the incidence of symptomatic aseptic meningitis and CSF leakage. These findings are consistent with those of previous studies that have reported lower rates of complications with arachnoid-preserving techniques than with traditional suboccipital decompression.

Pericranial grafts, cervical fascia, and allografts from different localizations were previously suggested as autologous grafts. Nevertheless, they do not have any clear superiority over one another [8,26,27]. In the present case series, grafts from the superficial cervical fascia just under the incision line were used, and there were no other complications, other than the small number of cases with superficial wound discharge. This method avoids possible surgical site complications that can arise from additional incisions and unnecessary incision enlargements, as well as the extra costs of using synthetic grafts.

In our cases, arachnoid layers were carefully preserved, and no related complications were seen. This result is compatible with the recent large research study suggesting that opening of the arachnoid layer exposes the subarachnoid space to cellular debris and blood supplies [28]. As the literature suggests, duraplasty is closely related to risks of CSF fistula and meningitis. Nevertheless, the reported CSF fistula and associated meningitis rates in the literature due to duraplasty decrease with arachnoid-preserving duraplasty, compared with that of arachnoid procedures. Arachnoid-preserving duraplasty is important to prevent the leakage of blood and the development of arachnoidal adhesions secondary to surgery. It is also important to point out that this surgical method shortens the duration of surgery. Therefore, as some authors suggest, arachnoid scaring is related to long-term negative results, and we agree with the recent studies asserting avoidance of the opening and extensive dissection of the layer [9,25,29,30].

Syrinx reduction or total resolution rates reach up to 90% in the limited number of studies that previously reported duraplasty without arachnoid dissection and suboccipital craniectomy [20,25,30]. In their series, Kemerdere et al presented the success of the arachnoid-preserving technique, with syrinx reduction in 76.1% of cases and total syrinx reduction in 23.8% [9]. We present a syrinx reduction in 83.3% of our cases and a total reduction (disappearance from all MRI sections) in 16.7%.

In the meta-analysis study conducted by Tavallaii et al, in which duraplasty and dura-splitting technique methods were compared, it was reported that syringomyelia disappeared in 21.4% of the cases, decreased in size in 61.5%, remained constant in 27%, and progressed in some; there was no significant difference in terms of clinical and radiological results [16]. On the contrary, in our series, all patients with syringomyelia presented with disappearance or significant reduction in size on their postoperative third-month follow-up. No cases showed progression.

One of the most important points that should be emphasized in our study is that the dural opening technique is linear – from the C1 dural level to the right or left cerebellar tonsil dura. This technique has been mentioned in limited numbers in the literature. Our series is the second largest after the publication of Kemerdere et al [9]. As seen in our series, the linear incision is quite safe, with low rates of complication and high rates of healing.

In addition to these results, the usage of no synthetic grafts or harvesting grafts from a different incision was important in reducing surgical duration and preventing complications. In terms of neurological improvement, our study showed that all included patients experienced significant improvement in their neurological symptoms after surgery. Specifically, we observed improvements in symptoms such as headache, neck pain, numbness, and weakness. This is consistent with previous studies that have reported good neurological outcomes with arachnoid-preserving suboccipital decompression.

Additionally, we found that patient satisfaction was high following surgery, with 100% of patients reporting satisfaction with the outcomes of their surgery. This suggests that arachnoid-preserving suboccipital decompression is a well-tolerated and effective surgical technique for the management of adult CMI with syringomyelia.

Despite the promising results, this study has limitations. The retrospective nature and the limited sample size can affect the generalizability of the findings. Additionally, the follow-up period, while adequate, could be extended in future studies to assess long-term outcomes more comprehensively. Further research with a larger cohort and a prospective study design would provide more robust evidence.

Conclusions

This study demonstrates that the linear, arachnoid-preserving suboccipital decompression technique is a safe, effective, and rapid alternative for treating adult patients with CM-I and syringomyelia. It offers significant improvements in neurological symptoms and high patient satisfaction. Compared to traditional methods, this technique notably reduces postoperative complications, particularly CSF leakage and arachnoiditis. Additionally, the absence of synthetic graft usage in this technique makes it more cost-effective, further enhancing its viability as a treatment option.