Type I Chiari Malformation Without Concomitant Bony Instability: Assessment of Different Surgical Procedures and Outcomes in 73 Patients

C1-C2 Fixation for Chiari with Syringomyelia Associated with Atlantoaxial Instability, Atlantooccipital Assimilation and an Anomalous Vertebral Artery Course

Chiari malformations, characterized by the herniation of cerebellar tonsils through the foramen magnum, are complex neurosurgical conditions that pose significant diagnostic and therapeutic challenges.1 Traditional interventions, such as foramen magnum decompression, have been the mainstay of treatment but are not universally effective, especially in cases with underlying atlantoaxial instability. However, recent studies highlight the importance of atlantoaxial instability in their pathogenesis, shifting the therapeutic focus towards atlantoaxial fixation.2 Research shows that atlantoaxial fixation can effectively address the underlying instability, leading to better symptomatic relief and neurological outcomes compared to traditional decompression methods.3,4-17 The findings from these studies consistently demonstrate that atlantoaxial instability is a critical factor in the development of Chiari malformations. Atlantoaxial fixation not only resolves the mechanical instability but also leads to significant symptomatic relief and improved neurological outcomes. Comparative analysis indicates superior efficacy of atlantoaxial fixation over traditional decompression techniques, especially in patients with concurrent basilar invagination and syringomyelia. This surgical Video 1 illustrates a case of a 20-year-old male patient with tonsillar herniation, syringomyelia, atlantooccipital assimilation, atlantoaxial instability, basilar invagination and dorsolumbar scoliosis, who was successfully managed with cervical fixation using a bilateral C1 lateral mass and C2 transpedicular screw construct. This surgery was able to achieve clinical and radiologic improvement without the need for a foramen magnum decompression. The patient consented to the procedure and to the publication of his images.

Individualized Functional Decompression Options for Adult Chiari Malformation With Syringomyelia and A Novel Scale for Syringomyelia Resolution: A Single-Center Experience

OBJECTIVE

To compare outcomes of posterior fossa bony decompression alone (PFD) versus PFD with duraplasty (PFDD) versus PFDD with additional obex exploration (PFDDO) in patients with Chiari malformation type I (CMI) combining syringomyelia.

METHODS

Clinical records of adult patients who underwent decompressions from 2014 to 2022 were retrospectively analyzed. The decompression procedure was individualized based on the cerebrospinal fluid pulse in the surgical field. The Chicago Chiari Outcome Scale (CCOS) was used to assess the prognosis of the patients and a novel syringomyelia resolution scale, based on 3-dimensional volume, was introduced. The percentage change in the cervical syrinx volume was classified as follows by resolution: ≥ 70%, 30%-70%, and < 30%.

RESULTS

Seventy-eight individuals were enrolled, of which 22, 20, and 36 underwent PFD, PFDD, and PFDDO, respectively. The three decompression groups had no significant difference in the preoperative characteristics and postoperative prognosis. Multivariate analyses revealed that better CCOS was significantly correlated with younger age at surgery (p = 0.018), syrinx originated from lower cervical levels (p = 0.037), narrower preoperative cerebral aqueduct (p = 0.005), and better syrinx volume resolution (p = 0.004). Additionally, a better cervical syrinx volume resolution was significantly correlated with higher CCOS (p = 0.017), narrower cerebral aqueduct (p = 0.035), and better tonsillar descent resolution (p = 0.007).

CONCLUSION

Individualized functional decompression induced an equal effect on CCOS and syrinx volume resolution for all CMI patients with syringomyelia. Our syringomyelia resolution scale facilitates communication and prediction of CMI prognosis.

Chiari Syndrome: Advances in Epidemiology and Pathogenesis: A Systematic Review

Arnold Chiari syndrome is a rare congenital disease of unknown prevalence and whose origin is still under study. It is encompassed within the posterior cranial malformations, showing a wide spectrum of symptomatology that can range from severe headache, dizziness, and paresthesia to complete asymptomatology. It is for this reason that early diagnosis of the disease is difficult, and it is usually diagnosed in adolescence. Treatment is based on remodeling and decompression of the malformed posterior cranial fossa, although the risk of residual symptoms after surgery is high. The aim of this review is to update all the existing information on this pathology by means of an exhaustive analysis covering all the scientific literature produced in the last 5 years. In addition, it has been carried out following the PRISMA model and registered in PROSPERO with code CRD42023394490. One of the main conclusions based on the results obtained in this review is that the origin of the syndrome could have a genetic basis and that the treatment of choice is the decompression of the posterior cerebral fossa.

Low versus High Intracranial Compliance in Adult Patients with Chiari Malformation Type 1-Comparison of Long-Term Outcome After Tailored Treatment

BACKGROUND

In patients with Chiari malformation type 1 (CMI) presenting with low intracranial compliance (ICC), foramen magnum decompression (FMD) often fails and the complication rate may be higher. We therefore routinely perform a preoperative assessment of ICC from intracranial pressure measurement. Patients with low ICC are treated with ventriculoperitoneal shunt (VPS) before FMD. In this study, we assess the outcome of patients with low ICC, compared with patients with high ICC treated with FMD alone.

METHODS

We reviewed the clinical and radiologic data of all consecutive patients with CMI treated between April 2008 and June 2021. ICC was assessed by overnight measurement of the pulsatile intracranial pressure: mean wave amplitude (MWA) above a previously defined threshold for abnormality was considered a surrogate marker for low ICC. The outcome was scored by Chicago Chiari Outcome Scale.

RESULTS

Of 73 patients, 23 with low ICC (average MWA 6.8 ± 1.2 mm Hg) received VPS before FMD, whereas 50 with high ICC (average MWA 4.4 ± 1.0 mm Hg) received only FMD. After a mean follow-up of 78.7 ± 41.4 months, 96% of all patients subjectively improved. The mean Chicago Chiari Outcome Scale score was 13.1 ± 2.2. Enlargement of cerebrospinal fluid space in the foramen magnum was achieved in 95% and regression of syringomyelia in 74% of cases. We found no significant difference in outcome between the patients with low and high ICC.

CONCLUSIONS

By identifying patients with CMI associated with low ICC and tailoring their treatment by VPS before FMD, we achieved favorable clinical and radiologic outcomes comparable to those with high ICC.

Relationship Between Syrinx Resolution and Cervical Sagittal Realignment Following Decompression Surgery for Chiari I Malformation Related Syringomyelia Based on Configuration Phenotypes

OBJECTIVE

Combined with different configuration types of syringomyelia, to analyze the correlation between syrinx resolution and changes in cervical sagittal alignment following Foramen magnum and Magendie dredging (FMMD) for syringomyelia associated with Chiari I malformation (CM-I), and to further explore the respective relationship with clinical outcome.

METHODS

A consecutive series of 127 patients with CM-I and syringomyelia who underwent FMMD in our center met the inclusion criteria of this study. Their clinical records and radiologic data were retrospectively reviewed. The Japanese Orthopedic Association (JOA) scoring system and the Chicago Chiari Outcome Scale (CCOS) were used to evaluate the surgical efficacy. The phenotypes of syringomyelia and the clinical characteristics of the patients were analyzed according to grouping by cervical curvature at baseline.

RESULTS

The preoperative straight or kyphotic cervical alignment is more common in the moniliform syrinx. After surgery, the syrinx resolution and cervical sagittal realignment in the moniliform group are more obvious, and the corresponding prognosis is relatively better. Spearman correlation analysis showed that the ΔS/C ratio (the change ratio of syrinx/cord) was positively correlated with the CCOS (p = 0.001, r = 0.897) and ΔC2-7A (the change of lower cervical angle) (p = 0.002, r = 0.560). There was also a correlation between the ΔJOA score (the change rate of the JOA score) and ΔC2-7A (p = 0.012, r = 0.467).

CONCLUSION

After decompression surgery, syrinx resolution may coexist with the changes in the subaxial lordosis angle, especially for syrinx in moniliform type, and the relationship between syrinx resolution and cervical sagittal realignment might be valuable for evaluating the surgical outcome.

Role of Atlas Assimilation in the Context of Craniocervical Junction Anomalies

Atlas assimilation (AA) may be associated with atlantoaxial dislocation, Chiari malformation (CM), and basilar invagination. The importance of AA in the context of craniocervical junction (CVJ) anomalies is unclear. Considering this context, this study's objective is to discuss the role of AA in the management of CVJ anomalies, especially in CM. A comprehensive literature review was performed. In addition, some illustrative cases were discussed on the basis of our review. Finally, we propose a theoretic algorithm to evaluate patients with AA and CM. AA is a proatlas segmentation anomaly that may be complete or incomplete. It may be totally asymptomatic or symptomatic as the result of transferred shifted forces onto the C1-2 joints, leading to clear instability (atlantoaxial dislocation) or mild C1-2 instability. Cautious surgical planning may be required due to associated vertebral artery anomalies. AA with concomitant C2-C3 segmentation failure is highly associated with late C1-C2 instability. CVJ decompression failure was reported in patients with CM and a low clivus canal angle (<130-135 degrees). Patients with assimilated anterior C1 arches usually have evident AAD. CM patients with AA generally have type 1 BI or type 2 BI and are reported with higher rates of CVJ instabilities when compared with those "pure" CM. Dynamic examinations may provide additional evidence of atlantoaxial instability. Although AA per se is not considered an unstable configuration, further and detailed evaluations of patients with CM associated with AA are necessary. Some associated unstable configurations required concomitant CVJ fixation.