103. An Alternative Morphological Parameter for Chiari I Malformations: A Retrospective Study

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Authors: William Fuell; Reem Elwy; Gregory Albert (Conway, AR)

Introduction:

Due to the significant presence of asymptomatic patients with Chiari I malformations (CMI) seen in pediatric neurosurgery, investigation of alternative morphological parameters in relation to symptomology could lead to revision of current diagnostic criteria. It is almost universally accepted that the caudal descent of the cerebellar tonsils from the posterior fossa into the upper cervical canal, of at least 5 mm below the McRae line, is the primary indicator for CMI pathology. Although tonsillar herniation may aid in guiding diagnosis, tissue density within the foramen magnum in relation to symptomatology has not been explored from a diagnostic perspective.

Methods:

We conducted a retrospective, longitudinal chart review of 465 pediatric CMI patients seen over a 6-year period. Patients that received surgical intervention were considered symptomatic and those who were treated conservatively and did not require surgery were considered asymptotic. Tissue density within the foramen magnum and tonsillar herniation were measured to determine which is a greater indicator for surgical intervention.

Results:

Of the 465 patients, 80 patients had surgical intervention and 385 were asymptomatic. The average tissue density was significantly greater (P-value < 0.0005) in surgical than asymptomatic patients with a density of 83.3% and 78.6% respectively. The average tonsillar descent for surgical patients was 10.6 mm compared to 9.8 mm for asymptomatic patients (p-value= 0.157).

Conclusion:

It is expected that tissue density within the foramen magnum is a greater indicator for CMI symptomatology leading to surgical intervention than tonsillar herniation. With the current criterion for CMI, a considerable fraction of CMI diagnoses are incidental findings that would have previously not required follow-up due to the lack of indication for disease progression. We propose further investigation into the revision of the steadfast 5 mm rule for diagnosing CMI patients.

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