Foramen Magnum Decompression with Duroplasty safe and effective for Type 1 Chiari Malformation

Foramen Magnum Decompression with Duroplasty is a simple, safe, and effective surgical procedure for adult CMI that yields significant and sustained improvement in clinical and radiological outcomes. However, clinical improvement does not always correlate with syringomyelia regression and cerebellar tonsillar shift.

Chiari malformation type I (CMI), the most common CM, is a craniocervical junction disorder characterized by caudal displacement of the cerebellar tonsils into the upper cervical canal through the foramen magnum. Typical symptoms include occipital headache, neck and shoulder pain, muscle weakness, numbness, and brainstem and cranial nerve dysfunction with broad clinical variations. It affects both children and adults and was initially reported in 1891 by Austrian pathologist Hans Chiari

CMI is a congenital disorder usually associated with syringomyelia. Numerous ideas exist regarding the pathophysiology of CM, including early hydrocephalus in the embryo, failure of the pons to fold normally, and mechanical traction of the spinal cord.Currently, the most widely accepted theory is posterior fossa congestion due to mesodermal hypoplasia. In addition, the small posterior fossa and falling hernia tonsils restrict the circulation of cerebrospinal fluid (CSF) and raise the cervical subarachnoid pulse pressure, resulting in syrinx development. Based on these theories, decompressive surgery has been widely approved for the treatment of symptomatic CMI.

Surgical decompression techniques include foramen magnum decompression with duraplasty (FMDD) or without. FMDD is one of the most common procedures for the treatment of symptomatic CMI, with the objective of relieving compression at the brainstem and restoring normal CSF flow. Despite vast surgical experience, the long-term (> 1 year) outcomes of FMDD remain variable and controversial, and there has been a lack of single large-sample investigations. Therefore, this study was conducted to evaluate the long-term prognosis of FMDD in adults with CMI in terms of symptom improvement, multiple scale scores, and imaging changes.

Based on the pathophysiology of CMI, the primary objectives of surgery are to restore normal CSF flow, eliminate and reduce the syrinx, and relieve brainstem compression. FMDD or FMD alone is the most frequently used surgical intervention to treat CMI with or without syringomyelia. As for comparing these two surgical procedures, many studies have concluded that both can result in a satisfactory prognosis with improvement rates of more than 60%. Moreover, FMDD may be more suitable for patients with CMI with a syrinx, despite a slightly higher complication rate, whereas FMD may be a preferred option in patients without syringomyelia because of its similar clinical improvement and lower complication rate.

Wang et al conducted a long term follow up study of patients operated with FMDD and found that most symptoms improved in more than 60% of patients, the overall clinical outcome improvement rate was around 63%, the syringomyelia regression rate was above 90%, and 83% of the patients had no continued cerebellar tonsil descent. In their analysis of the postoperative changes in symptoms, the most favorable long-term results were noted among the patients with cranial nerve symptoms; 80% of them improved, and none experienced late deterioration. They believe that duraplasty is an important factor that not only establishes the free flow of CSF but also provides more space to decompress the brainstem and upper cervical spinal cord. The worst symptom recovery was observed in the individuals with motor impairments, which may be attributable to the irreversible destruction of anterior horn cells by the syrinx. The overall long-term clinical outcomes were satisfactory, with marked improvement in 62.5% and stabilization in 31.8%. These results suggest that FMDD can lead to significant and sustained long-term clinical improvement.

Despite the variable incidence of postoperative radiological syrinx improvement, FMDD may be a more appropriate therapy for Chiari-associated syringomyelia. “We believe that FMDD is sufficient for the decompression and restoration of normal or near-normal CSF circulation at the craniocervical junction”, say the authors. The authors also demonstrated that the cerebellar tonsils did not continue to descend following surgery in most patients, emphasizing the significance of duraplasty for more space in the craniocervical junction.

The results of the studiy also suggest a significantly valid absence of a correlation between tonsil ascent and syringomyelia reduction.which was attributed to tonsillar herniation as the triggering factor leading to syringomyelia formation and that the extent of syrinx expansion did not correlate with the degree of tonsillar herniation. In other words, cerebellar tonsillectomy was not necessary for syringomyelia reduction.

“Our findings suggest that FMDD is a simple, safe, and effective surgical procedure for adults with CMI with or without syringomyelia. This surgical procedure significantly alleviates brainstem compression symptoms, improves or stabilizes symptoms associated with syringomyelia, and yields significant and sustained improvement in clinical and radiological outcomes. However, clinical improvement does not always correlate with syringomyelia regression and cerebellar tonsillar shift”, they conclude.

Reference

Wang, B., Wang, C., Zhang, Y., Liang, Y., Liu, W., Yang, J., Xu, Y., Wang, Y., & Jia, W. (2023). Long-term outcomes of foramen magnum decompression with duraplasty for Chiari malformation type I in adults: a series of 297 patients, Neurosurgical Focus, 54(3), E5. Retrieved Mar 28, 2023, from

Doi: https://doi.org/10.3171/2022.12.FOCUS22627