Atlantoaxial fixation for failed foramen magnum decompression in patients with Chiari formation

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.

Respiratory arrest after posterior fossa decompression in patients with Chiari malformations: An overview

Background

Chiari malformation type 1 (CM1) is a structural abnormality in the skull and cerebellum, causing cerebellar tonsils to shift downward. Decompression of the posterior fossa is a common surgical method to relieve symptoms and prevent neurological deterioration. After posterior fossa decompression (PFD), individuals with CM1 were more likely to have respiratory arrest. Here, we present, for the first time, a comprehensive overview of the potential risk factors and causes of respiratory arrest following PFD.

Methods

A review of the literature highlighting the risk factors for postoperative respiratory arrest in CM1 patients was conducted in the databases of PubMed, Medline, and Google Scholar.

Results

Patients with syringomyelia and CM1 are at increased risk for respiratory arrest due to a number of factors, including impaired respiratory mechanics, central respiratory center dysfunction from edema or ischemia, intraoperative brain stem ischemia, and delayed gastric emptying from autonomic dysfunction. Occipitalization of the first cervical vertebra, basilar impression, and fusion of C2-C3 are all risk factors for respiratory arrest.

Conclusion

Implications for CM1 patient care and prospects for further investigation of postoperative respiratory arrest's causes and risk factors were discussed.

Evolving Concepts of Craniovertebral and Spinal Instability

Weakness of the muscles of the nape of the neck and back of the spine and its related instability is the nodal point of pathogenesis of a number of clinical and pathological events at the craniovertebral junction and the spine. Whilst acute instability results in sudden and relatively severe symptoms, chronic or long-standing instability is associated with a range of musculoskeletal and structural spinal alterations. Telescoping of the spinal segments results in "vertical" spinal instability in the subaxial spine and central or axial atlantoaxial instability (CAAD) at the craniovertebral junction. Instability in such cases might not be observed on dynamic radiological imaging. Chiari formation, basilar invagination, syringomyelia, and Klippel-Feil alteration are some of the secondary alterations as a result of chronic atlantoaxial instability. Radiculopathy/myelopathy related to spinal degeneration or ossification of posterior longitudinal ligament appears to have their origin from vertical spinal instability. All the secondary alterations in the craniovertebral junction and subaxial spine that are traditionally considered pathological and to have compressive and deforming role are essentially protective in nature, are indicative of instability, and are potentially reversible following atlantoaxial stabilization. Stabilization of unstable spinal segments is the basis of surgical treatment.

Is C1-C2 Reduction and Fixation A Good Choice in the Treatment of Recurrent Chiari-Like Symptoms With Syringomyelia?

BACKGROUND

Foramen magnum decompression (FMD) is the first-choice treatment for Chiari malformation (CM). However, it has been suggested that cerebellar herniation and syringomyelia occur as a natural protective event to prevent neural damage caused by atlantoaxial instability. It is argued that treating instability is the main treatment. Positive results of atlantoaxial fusion have been reported in the literature, but there are no studies including the results of atlantoaxial fusion as the second treatment in patients in whom classical decompression failed. In our study, we report the results of these patients to help in the selection of treatment and we present our treatment algorithm for CM with syringomyelia.

METHODS

Thirteen patients who had undergone FMD and duraplasty due to CM and syringomyelia in our clinics and who had recovered clinically and radiologically but had recurrent complaints during long-term follow-up were evaluated. C1-C2 distraction and fusion were performed. We evaluated these patients radiologically and clinically.

RESULTS

The mean age of the 13 patients was found to be 32.4 years. Male to female ratio was 6:7. The complaints recurred after an average of 2.1 years. Also, 3 cases were presented with their clinical characteristics and radiologic findings.

CONCLUSIONS

FMD may fail even with duraplasty, and treatment of CM in recurrent cases is still controversial. Recently, atlantoaxial instability has been reported to be the main pathology of CM, and the cure for pathology is to treat instability. Recurrent CMs with syringomyelia in which FMD has failed should be treated by atlantoaxial fixation.