Introduction: The aim of this study was to determine the peak cerebrospinal fluid (CSF) flow velocity at the foramen magnum level in adult patients with Chiari type 1 malformation (CM1) and to determine the changes in velocity after posterior fossa decompression. An attempt was also made to determine whether or not CSF flow velocity can be a significant predictor in patients who need surgical intervention.
Materials and methods: A prospective longitudinal study was conducted in 32 symptomatic patients of CM1 treated with craniocervical decompression. Only adult patients with age ≥18 years and tonsillar herniation ≥5 mm were included in this study. Clinical and radiological assessment of patients with reference to their CSF flow characteristics was done both preoperatively and after suboccipital decompression.
Results: Out of the 32 patients, 30 patients underwent a suboccipital decompression and two patients were treated with a venriculoperitoneal shunt procedure due to gross hydrocephalus. The preoperative mean tonsillar herniation was 10.4 ± 4.64 mm that reduced to 7.35 ± 3.10 mm in the follow up period. Postoperatively, there was also a substantial decrease in the peak CSF velocity at the foramen magnum along with reduction in the extent and size of the syrinx. These changes in CSF velocity correlated with a more normal appearing foramen magnum and an improvement in symptoms.
Conclusion: Although the selection criteria for surgery are based mainly on the degree of tonsillar ectopia and presenting symptoms, the degree of CSF flow obstruction rather than the degree of tonsillar herniation can better select patients who are most responsive to surgery. An improved CSF velocity profile following surgery in such patients is a useful guide to anticipate a symptomatic improvement.
Keywords: Chiari 1 malformation; foramen magnum decompression; posterior fossa decompression; syringomyelia.