The effect of posterior fossa decompression in adult Chiari malformation and basilar invagination: a systematic review and meta-analysis

Biomechanical Study of Atlanto-occipital Instability in Type II Basilar Invagination: A Finite Element Analysis

OBJECTIVE

Recent studies indicate that 3 morphological types of atlanto-occipital joint (AOJ) exist in the craniovertebral junction and are associated with type II basilar invagination (BI) and atlanto-occipital instability. However, the actual biomechanical effects remain unclear. This study aims to investigate biomechanical differences among AOJ types I, II, and III, and provide further evidence of atlanto-occipital instability in type II BI.

METHODS

Models of bilateral AOJ containing various AOJ types were created, including I-I, I-II, II-II, II-III, and III-III models, with increasing AOJ dysplasia across models. Then, 1.5 Nm torque simulated cervical motions. The range of motion (ROM), ligament and joint stress, and basion-dental interval (BDI) were analyzed.

RESULTS

The C0-1 ROM and accompanying rotational ROM increased progressively from model I-I to model III-III, with the ROM of model III-III showing increases between 27.3% and 123.8% indicating ultra-mobility and instability. In contrast, the C1-2 ROM changes were minimal. Meanwhile, the stress distribution pattern was disrupted; in particular, the C1 superior facet stress was concentrated centrally and decreased substantially across the models. The stress on the C0-1 capsule ligament decreased during cervical flexion and increased during bending and rotating loading. In addition, BDI gradually decreased across the models. Further analysis revealed that the dens showed an increase of 110.1% superiorly and 11.4% posteriorly, indicating an increased risk of spinal cord impingement.

CONCLUSION

Progressive AOJ incongruity critically disrupts supportive tissue loading, enabling incremental atlanto-occipital instability. AOJ dysplasia plays a key biomechanical role in the pathogenesis of type II BI.

Evaluating the Need for Durotomy and Duraplasty in Adults Undergoing Suboccipital Craniectomy for Chiari Decompression: A Case Series Analysis of Radiographic and Clinical Outcomes

Background Suboccipital craniectomy (SOC) in conjunction with dura opening and duraplasty for posterior fossa decompression is an effective treatment for symptomatic Chiari 1 malformations (CM1), primarily carried out in the pediatric population. However, dural opening and reconstruction are associated with an increased risk of complications, and their necessity in the adult population has not yet been robustly demonstrated. Given differences in clinical presentation and disease severity between the pediatric and adult patients, we aimed to identify if SOC alone with intraoperative ultrasound confirmation of adequate restoration of pulsatile motion of cerebellar tonsil is sufficient to treat symptomatic CM1 while mitigating surgical risks. Methods We identified a retrospective, institutional cohort of adult patients who underwent SOC for Chiari decompression between 2014 and 2023. Demographic, clinical, and radiographic features were extracted for each patient. Clinical outcomes were assessed using the Chicago Chiari Outcome Scale (CCOS) and Motor-Sensory-Sphincter signs score (Clinical Sign Score (CSS)). Radiographic outcomes assessed cerebellar ectopia and associated syrinx characteristics. Results A total of 15 patients were identified, with an average follow-up period of three years. Eight patients underwent SOC with duraplasty, whereas seven patients underwent SOC only without duraplasty. Both groups of patients were of similar age at surgery and had similar nature and duration of symptoms prior to surgery. On pre-operative radiographic evaluation, both groups of patients had similar lengths of cerebellar ectopia (9.9±11.0 mm to 11.1±5.7 mm, p=0.591), and associated syrinxes (75% vs. 42.9%, p=0.205). Intraoperatively, both groups had similar estimated blood losses, though the length of surgery was significantly shorter when durotomy was spared (202±58.3 minutes to 116.3±47.8 minutes, p=0.011). The length of ICU stay was also significantly longer in the durotomy group (1.1±0.6 days to 0.0 days, p<0.001). Neither group reported any post-operative complications. On follow-up, both groups demonstrated similar reductions in cerebellar ectopia and syrinx characteristics. Clinically, the CCOS and CSS scores were similar between the two cohorts at follow-up, with no repeat surgery required in either group. Conclusion Our cohort suggests that for adult CM1 patients, SOC decompression alone without dural reconstruction might lead to comparable clinical and radiographic outcomes to SOC decompression with durotomy/duraplasty, especially if intraoperative ultrasound confirms good cerebrospinal fluid (CSF) flow after SOC. Notably, sparing durotomy and duraplasty is also associated with decreased operative time and decreased ICU stay.

Treatment of Chiari malformations with craniovertebral junction anomalies: Where do we stand today?

Background

Chiari malformation type 1 (CM-1) is characterized by cerebellar tonsil herniation through the foramen magnum and can be associated with additional craniovertebral junction anomalies (CVJA). The pathophysiology and treatment for CM-1 with CVJA (CM-CVJA) is debated.

Objective

To evaluate the trends and outcomes of surgical interventions for patients with CM-CVJA.

Methods

A systematic review of the literature was performed to obtain articles describing surgical interventions for patients with CM-CVJA. Articles included were case series describing surgical approach; reviews were excluded. Variables evaluated included patient characteristics, approach, and postoperative outcomes.

Results

The initial query yielded 403 articles. Twelve articles, published between 1998-2020, met inclusion criteria. From these included articles, 449 patients underwent surgical interventions for CM-CVJA. The most common CVJAs included basilar invagination (BI) (338, 75.3%), atlantoaxial dislocation (68, 15.1%) odontoid process retroflexion (43, 9.6%), and medullary kink (36, 8.0%). Operations described included posterior fossa decompression (PFD), transoral (TO) decompression, and posterior arthrodesis with either occipitocervical fusion (OCF) or atlantoaxial fusion. Early studies described good results using combined ventral and posterior decompression. More recent articles described positive outcomes with PFD or posterior arthrodesis in combination or alone. Treatment failure was described in patients with PFD alone that later required posterior arthrodesis. Additionally, reports of treatment success with posterior arthrodesis without PFD was seen.

Conclusion

Patients with CM-CVJA appear to benefit from posterior arthrodesis with or without decompressive procedures. Further definition of the pathophysiology of craniocervical anomalies is warranted to identify patient selection criteria and ideal level of fixation.

Intra-articular Distraction Versus Decompression to Treat Basilar Invagination Without Atlantoaxial Dislocation: A Retrospective Cohort Study of 54 Patients

OBJECTIVE

The surgical management of basilar invagination without atlantoaxial dislocation (type B basilar invagination) remains controversial. Hence, we have reported the use of posterior intra-articular C1-2 facet distraction, fixation, and cantilever technique versus foramen magnum decompression in treating type B basilar invagination as well as the results and surgical indications for this procedure.

METHODS

This was a single-center retrospective cohort study. Fifty-four patients who underwent intra-articular distraction, fixation, and cantilever reduction (experimental group) and foramen magnum decompression (control group) were enrolled in this study. Distance from odontoid tip to Chamberlain's line, clivus-canal angle, cervicomedullary angle, craniovertebral junction (CVJ) triangle area, width of subarachnoid space and syrinx were used for radiographic assessment. Japanese Orthopedic Association (JOA) scores and 12-item Short Form health survey (SF-12) scores were used for clinical assessment.

RESULTS

All patients in the experimental group had a better reduction of basilar invagination and better relief of pressure on nerves. JOA scores and SF-12 scores also had better improvements in the experimental group postoperation. SF-12 score improvement was associated with preoperative CVJ triangle area (Pearson index, 0.515; p = 0.004), cutoff value of 2.00 cm2 indicating the surgical indication of our technique. No severe complications or infections occurred.

CONCLUSION

Posterior intra-articular C1-2 facet distraction, fixation, and cantilever reduction technique is an effective treatment for type B basilar invagination. As various factors involved, other treatment strategies should also be investigated.

Effect of modified clivoaxial angle on surgical decision making and treatment outcomes in patients with Chiari malformation type 1

Introduction

Chiari malformation type 1 (CM1), a complex pathological developmental disorder of the craniovertebral junction, is typically characterized by herniation of the cerebellar tonsils from the foramen magnum. Treatment using posterior fossa decompression alone without taking the ventral cervico-medullary compression into consideration may lead to unsatisfactory treatment outcomes. The current study evaluated the utility of the modified clivoaxial angle (MCAA) in assessing ventral compression and also examined its effect on treatment outcomes.

Method

This retrospective study included 215 adult patients who underwent surgical treatment for CM1 at one medical center over a 10-year period. The following surgical techniques were used to decompress the posterior fossa: (a) PFD: bone removal only; (b) PFDwD: bone removal with duraplasty; and (c) CTR: cerebellar tonsil resection. The morphometric measurements of the craniovertebral junction (including MCAA) were recorded using preoperative images, and the postoperative clinical status was evaluated using the Chicago Chiari outcome scale (CCOS).

Results

MCAA was positively correlated with the CCOS score and also independently predicted treatment outcome. To enable Receiver operating characteristic (ROC) curve analysis of CCOS scores, the patients were divided into three groups based on the MCAA cut-off values, as follows: (a) severe (n = 43): MCAA ≤ 126; (b) moderate (n = 86): 126 < MCAA ≤ 138; and (c) mild (n = 86): MCAA > 138. Group a exhibited severe ventral cervico-medullary compression (VCMC), and their CCOS scores for the PFD, PFDwD, and CTR groups were 11.01 ± 1.2, 11.24 ± 1.3, and 13.01 ± 1.2, respectively (p < 0.05). The CCOS scores increased with widening of the MCAA angle in all surgical groups (p < 0.05). Furthermore, patients with mild MCAA (>138°) exhibited 78% regression of syringomyelia, and this was significantly greater than that observed in the other groups.

Discussion

MCAA can be used in the selection of appropriate surgical techniques and prediction of treatment outcomes, highlighting the importance of preoperative evaluation of ventral clivoaxial compression in patients with CM1.

Diagnosis and treatment of Chiari malformation and syringomyelia in adults: international consensus document

BACKGROUND

Syringomyelia and Chiari malformation are classified as rare diseases on Orphanet, but international guidelines on diagnostic criteria and case definition are missing.

AIM OF THE STUDY

to reach a consensus among international experts on controversial issues in diagnosis and treatment of Chiari 1 malformation and syringomyelia in adults.

METHODS

A multidisciplinary panel of the Chiari and Syringomyelia Consortium (4 neurosurgeons, 2 neurologists, 1 neuroradiologist, 1 pediatric neurologist) appointed an international Jury of experts to elaborate a consensus document. After an evidence-based review and further discussions, 63 draft statements grouped in 4 domains (definition and classification/planning/surgery/isolated syringomyelia) were formulated. A Jury of 32 experts in the field of diagnosis and treatment of Chiari and syringomyelia and patient representatives were invited to take part in a three-round Delphi process. The Jury received a structured questionnaire containing the 63 statements, each to be voted on a 4-point Likert-type scale and commented. Statements with agreement <75% were revised and entered round 2. Round 3 was face-to-face, during the Chiari Consensus Conference (Milan, November 2019).

RESULTS

Thirty-one out of 32 Jury members (6 neurologists, 4 neuroradiologists, 19 neurosurgeons, and 2 patient association representatives) participated in the consensus. After round 2, a consensus was reached on 57/63 statements (90.5%). The six difficult statements were revised and voted in round 3, and the whole set of statements was further discussed and approved.

CONCLUSIONS

The consensus document consists of 63 statements which benefited from expert discussion and fine-tuning, serving clinicians and researchers following adults with Chiari and syringomyelia.

Occipital condyle screw fixation after posterior decompression for Chiari malformation: Technical report and application

BACKGROUND

Surgical techniques for stabilization of the occipital cervical junction have traditionally consisted of screw-based techniques applied in conjunction with occipital plating and rods connected to subaxial instrumentation in the form of pars, pedicle, or lateral mass screws. In patients with type 1 Chiari malformation (CM-1) and evidence of occipital cervical junction instability who have undergone posterior decompression, the occipital condyle (OC) represents a potential alternative cranial fixation point. To date, this technique has only been described in pediatric case reports and morphometric cadaver studies.

METHODS

Patients underwent posterior fossa decompression for treatment of CM. Subsequently, patients received occipital cervical stabilization using OC screws.

RESULTS

Patients were successfully treated with no post-operative morbidity. Patient 2 was found to have pseudoarthrosis and underwent revision. Both patients continue to do well at 1-year follow-up.

CONCLUSION

Placement of the OC screw offers advantages over traditional plate-based occipital fixation in that bone removal for suboccipital decompression is not compromised by the need for hardware placement, screws are hidden underneath ample soft tissue in patients with thin skin which prevents erosion, and the OC consists of primarily cortical bone which provides for robust tricortical fixation. These cases demonstrate the novel application of the OC screw fixation technique to the treatment of occipital cervical junction instability in adult patients undergoing simultaneous posterior fossa decompression.

Foramen Magnum Angle: A New Parameter for Basilar Invagination of Type B

OBJECTIVE

To describe the foramen magnum angle (FMA) as a new parameter for basilar invagination (BI) type B.

METHODS

The FMA was performed on sagittal slice of magnetic resonance imaging (MRI) as a line from the hard palate to the opisthion (angle vertex), and another line from the opisthion to the basion. The MRIs from 31 participants with BI type B and 96 controls were used. Intraclass correlation coefficient, descriptive data, and receiver operating characteristic (ROC) curve were used for statistical analysis at the 95% confidence interval.

RESULTS

The interobserver agreement of the FMA was 0.952. Patients with BI type B had a FMA significantly greater (25.9° ± 9.3°) than control participants (11.6° ± 4.9°) (P < 0.001). The area under the ROC curve showed a diagnostic value of 0.947. The FMA showed sensitivity 0.900 and specificity 0.854 for the cutoff criterion 17° (P < 0.001).

CONCLUSIONS

The FMA had an optimal diagnostic value that provided complementary evidence to investigate BI type B.

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

BACKGROUND

The best surgical treatment for adult Chiari malformation type 1 remains widely debated.

OBJECTIVE

This study aimed to assess the efficacy of posterior fossa decompression and duraplasty with arachnoid preservation compared with arachnoid dissection for the treatment of adult Chiari malformation type 1.

METHODS

Two reviewers (M.O.-G. and M.A.) performed a PubMed, MEDLINE, and Embase literature search using the following terms: ("Chiari" OR "Chiari 1") AND ("duraplasty" OR "arachnoid preservation" OR "arachnoid spar∗" OR "posterior fossa surgery" OR "posterior fossa decompression" OR "foramen magnum decompression"). Studies assessing the efficacy of posterior fossa decompression with duraplasty for the treatment of patients aged >18 years with Chiari malformation type 1 were included. Case reports with <10 patients, editorials, and non-English studies were excluded.

RESULTS

Of 195 studies identified, 24 were included for meta-analysis. In the 1006 participants, there was no difference in postoperative clinical or radiologic improvement between the 2 techniques. Patients who underwent posterior fossa decompression with duraplasty and arachnoid dissection had a greater prevalence of total complications (0.20, 95% confidence interval [CI], 0.13-0.29 vs. 0.09, 95% CI, 0.05-0.14; Q = 6.47; P = 0.01) and cerebrospinal fluid-related complications (0.15, 95% CI, 0.10-0.22 vs. 0.05, 95% CI, 0.02-0.12; Q = 4.88; P = 0.03) compared with arachnoid preservation. Furthermore, the prevalence of reoperation in the arachnoid dissection group was 25 times greater than in the arachnoid preservation group (0.08, 95% CI, 0.06-0.10 vs. 0.003, 95% CI, 0.00-0.02; Q = 10.73; P > 0.001).

CONCLUSIONS

Posterior fossa decompression and duraplasty with arachnoid preservation is a beneficial technique to treat Chiari malformation type 1 and reduces the risk of complications, particularly cerebrospinal fluid-related complications and the rate of reoperation.

Natural History and Conservative Treatment Options in Chiari Malformation Type I in Adults: A Literature Update

Over the years, knowledge regarding the natural history of Chiari malformation type I (CM-I) has improved. However, there are still uncertainties in the literature regarding asymptomatic and oligosymptomatic patients with CM-I. We performed a literature review in order to determine the natural history of CM-I in symptomatic patients who were not operated and in asymptomatic adult patients. Among symptomatic patients, the most frequent symptom was headache (77%). Cough-related headache alone (34%), migraine-related headache alone (21.4%), and both cough- and migraine-related headaches (21.8%) were the most prevalent forms of headache. Some symptoms improved more effectively with surgical treatment options; cough-related headaches improved by 95% following surgery and by 40% following conservative treatment. Other headache types improved by 93% and 61.5% following conservative and surgical treatments, respectively. Patients diagnosed with asymptomatic or oligosymptomatic CM-I may improve over time or stabilize with conservative treatment. There is great heterogeneity in the literature regarding the diagnostic criteria for CM-I. Owing to the heterogeneity among the articles identified for this review, there is no consensus regarding the precise indications for surgery in asymptomatic patients. The natural CM-I history in asymptomatic patients reveals a favorable evolution.

Chiari malformation type I and basilar invagination originating from atlantoaxial instability: a literature review and critical analysis

Introduction

Recently, a novel hypothesis has been proposed concerning the origin of craniovertebral junction (CVJ) abnormalities. Commonly found in patients with these entities, atlantoaxial instability has been suspected to cause both Chiari malformation type I and basilar invagination, which renders the tried and tested surgical decompression strategy ineffective. In turn, C1-2 fusion is proposed as a single solution for all CVJ abnormalities, and a revised definition of atlantoaxial instability sees patients both with and without radiographic evidence of instability undergo fusion, instead relying on the intraoperative assessment of the atlantoaxial joints to confirm instability.

Methods

The authors conducted a comprehensive narrative review of literature and evidence covering this recently emerged hypothesis. The proposed pathomechanisms are discussed and contextualized with published literature.

Conclusion

The existing evidence is evaluated for supporting or opposing sole posterior C1-2 fusion in patients with CVJ abnormalities and compared with reported outcomes for conventional surgical strategies such as posterior fossa decompression, occipitocervical fusion, and anterior decompression. At present, there is insufficient evidence supporting the hypothesis of atlantoaxial instability being the common progenitor for CVJ abnormalities. Abolishing tried and tested surgical procedures in favor of a single universal approach would thus be unwarranted.

Comparison of surgical outcomes in patients with Chiari Type I malformation receiving posterior fossa decompression with and without duraplasty

PURPOSE

The goals of this study were to compare clinical outcomes in patients with Chiari Malformation Type I (CMI) receiving posterior fossa decompression with (PFDD) or without duraplasty (PFD).

METHODS

We conducted a retrospective analysis of 178 consecutive cases of 157 patients undergoing PFDD or PFD for CMI at Cohen Children's Medical Center between 2007 and 2017. Clinical improvement was defined as a clear reduction of preoperative symptoms after surgery as reported by patients and parents. An improvement of syrinx was derived from radiologic comparison of pre- and postoperative MR imaging. Chi-square analysis was performed to analyze the association between duraplasty and clinical parameters (alpha = 0.05).

RESULTS

The primary presenting complaint was headache (142/178; 80%), followed by neck, back, and upper extremity pain, and numbness or tingling (49/178; 28%). Seventy patients (78/178; 44%) underwent PFD, and 100 patients (100/178; 56%) underwent PFDD. Overall, 143 patients (143/178; 80%) experienced subjective improvement with no statistically significant difference between the two surgical techniques (p = 0.705). The number of patients receiving PFDD with syrinx improvement or stabilization (55/59; 93%) was statistically larger than those that received PFD (8/13; 62%) (p = 0.008). PFDD was associated with greater complications than PFD alone. There were 35 cases of reoperation overall (35/178; 19%), and there was no statistically significant difference in reoperation rate between PFD and PFDD (p = 0.255).

CONCLUSIONS

There appears to be a role for PFDD in patients with severe syringomyelia, but overall, PFD alone may be safely offered as the initial surgical intervention for symptomatic CMI patients.

Failed Foramen Magnum Decompression in Chiari I Malformation Is Associated With Failure to Restore Normal Intracranial Compliance: An Observational Cohort Study

BACKGROUND

The standard treatment for symptomatic Chiari malformation (CM) I is foramen magnum decompression (FMD) to facilitate cerebral spinal fluid flow through the foramen magnum, improve intracranial compliance, and alleviate symptoms (commonly headache). This procedure has a variable success rate, with a significant proportion of patients having persistent symptoms after surgery.

OBJECTIVE

To investigate intracranial pressure (ICP) hydrodynamics in symptomatic surgery-naïve patients with CM I and symptomatic patients who have had prior FMD.

METHODS

We undertook a retrospective, observational cohort study, extracting data from our departmental ICP database. Patients with untreated ("Virgin") Chiari malformations (VCM), patients with previous "failed" FMD (ie, with persistent classical Chiari symptoms) (fFMD) and a normal control group, all with existing continuous ICP monitoring date were included. Median ICP (mICP) and median pulse amplitude (mPA) were compared between the groups.

RESULTS

A total of 33 CM patients (22 VCM and 11 fFMD) and 42 normal controls were included for analysis. mICP did not differ significantly between the normal control, VCM, and fFMD groups. mPA in the VCM and fFMD groups was significantly higher than the control group (P < .01 and P < .05, respectively).

CONCLUSION

In this cohort, patients with persistent symptoms after FMD have persistently impaired intracranial compliance, similar to patients who have not undergone surgery at all when compared with a control group. The reasons for this are not clear, and further research is required to establish the causation and optimum management for failed FMD.

Posterior Fossa Dimensions of Chiari Malformation Patients Compared with Normal Subjects: Systematic Review and Meta-Analysis

BACKGROUND

Chiari malformation (CM) is defined as a herniation of cerebellar tonsils below the foramen magnum and is considered to be due to underdevelopment of posterior fossa (PF) bone components. There is overcrowding of neural structures, and normal cerebrospinal fluid circulation is frequently blocked. Although several publications exist of measurements of dimensions and volumes from bone components of PF in CM, there is no systematic review evaluating quantitatively these dimensions. The aim of this study was to evaluate PF dimensions and volumes in a meta-analysis.

METHODS

An electronic search using PubMed and Google Scholar was done. Study eligibility criteria were defined by the PICO strategy, which selected patients and interventions. Studies comparing PF dimensions between patients with CM and normal subjects were selected. A meta-analysis of pooled data was done using statistical software.

RESULTS

Data for pooled analysis were obtained from 12 studies. Data synthesis was based on small published sample sizes in the majority of studies. Key findings included smaller measurements of clivus, supraoccipital bone, and PF area dimensions in patients with CM compared with normal subjects. Brainstem and cerebellar length was not different between groups.

CONCLUSIONS

This review provides evidence of smaller measurements of clivus, supraoccipital bone, and PF area dimensions in patients with CM compared with normal subjects. An implication of the key findings is that surgical treatment of CMs should consider the smaller dimensions of PF in planning.

Statistical Shape Analysis of Cerebellum in Patients With Chiari Malformation I

The surgical procedure is viewed as a typical treatment choice for patients with Chiari malformation (CM). Decompression is the preferred method for surgery, but it is not always possible to understand whether decompression has been successful especially in an early period. The present study focuses on investigating the shape differences in the cerebellums of Chiari patients compared with healthy controls, and to assess the clinical application of this situation whether if present. The MRI scans were reviewed retrospectively. Cerebellar data were obtained from the digital images and 9 anthropometric landmarks were marked on each image. Shape difference was assessed by performing Generalized Procrustes analysis. The cerebellar shape deformation from control to the patient was evaluated performing the Thin Plate Spline approach. There is a statistically significant cerebellar shape difference between groups. Highest deformation was determined at the cerebellar tonsillar inferior area, posterior of the uvula, and anterior of inferior medullary velum. The present study demonstrated cerebellar shape differences in CM I patients using a landmark-based geometric morphometric approach, considering the topographic distribution of cerebellum for the first time.

Significance of Modified Clivoaxial Angles in the Treatment of Adult Chiari Malformation Type I

OBJECTIVE

To investigate the influence of modified clivoaxial angle (MCAA) on the surgical planning and outcome in adult patients with Chiari malformation type I.

METHODS

Clinical data of 268 adult patients undergoing posterior fossa decompression without (PFD) or with duraplasty (PFDD) or with resection of tonsils (RT) for Chiari malformation type I over 10 years were reviewed retrospectively, with outcome evaluated by Chicago Chiari Outcome Scale (CCOS) score. By means of receiver operating characteristic curve, the threshold of MCAA was calculated to stratify the patients.

RESULTS

MCAA was positively correlated with CCOS score. In the MCAA ≤ 127° group (n = 57) with severe ventral cervicomedullary compression (VCMC), CCOS score of PFD, PFDD, and RT was 11.00, 11.06, and 12.42 (P < 0.05), respectively. In the 127° < MCAA ≤ 138° group (n = 87) with moderate VCMC, CCOS score of PFD, PFDD, and RT was 11.71, 12.72, and 13.00 (P < 0.01), respectively. In the MCAA > 138° group (n = 124) with mild or no VCMC, CCOS score of PFD, PFDD, and RT was 13.19, 13.90, and 13.67 (P < 0.05), respectively. The mean MCAA increased by 4.4° postoperatively (P < 0.05), which was positively associated with syringomyelia shrinkage.

CONCLUSIONS

MCAA may play a role in guiding the surgical treatment and predicting the prognosis in adult CMI patients. The larger the MCAA, the less invasive surgery is preferred with higher CCOS. PFDD should be the first choice in patients with mild or no VCMC (MCAA >138°) and RT in patients with moderate VCMC (127° < MCAA ≤ 138°). For patients with severe VCMC (MCAA ≤ 127°), RT could be considered as the primary surgery with awareness of the possible insufficiency of posterior decompression alone.

Sequential Enlargement of Posterior Fossa After Duraplasty for Chiari Malformation Type 1

Objective

There are several material options for duraplasty in surgery for foramen magnum decompression (FMD). We retrospectively analyzed surgical results and the impact of sequential alteration of posterior fossa (PF) size in patients with Chiari malformation type 1 after duraplasty using local fascia.

Methods

The patients with Chiari malformation type 1 who underwent FMD with duraplasty using local fascia at our institution between 2004 and 2015 were included in the study. Some pediatric patients who underwent FMD without duraplasty and patients with insufficient follow-up data were excluded. Improvement of clinical signs, regression of syrinx, and temporal alteration of PF size were analyzed with perioperative magnetic resonance imaging. Postoperative clinical outcomes were evaluated at the final follow-up using the Chicago Chiari Outcome Scale. Correlations between the PF size alteration and size of dural patch or Chicago Chiari Outcome Scale were statistically analyzed.

Results

Twelve patients were included in this study. The mean age of the patients was 31.9 (range, 18–48) years. Syrinx was incorporated in 11 patients and regressed postoperatively in all patients. The PF was significantly enlarged sequentially over time (P < 0.05). The degree of enlargement was positively correlated with size of the fascial patch (r = 0.540). Postoperative clinical outcomes at final follow-up were positively correlated with the degree of PF enlargement (r = 0.678).

Conclusions

The PF was enlarged sequentially over time after duraplasty using local fascia. The degree of enlargement was positively correlated with the size of the fascial patch and the likelihood of a favorable postoperative outcome.