CSF stroke volume measured in pediatric Chiari type 1 Malformation subjects before and after posterior fossa decompression surgery compared with healthy subjects.

Abstract

Background: Chiari Malformation Type 1 (CM-1) is characterized radiologically by > 5 mm herniation of the cerebellar tonsils below the foramen magnum (FM). Tonsillar descent below the FM does not correlate well with symptom severity nor does it predict outcomes following posterior-fossa-decompression surgery. Using 2D phase-contrast magnetic resonance imaging (MRI) it is possible to measure cerebrospinal fluid (CSF) hydrodynamics non-invasively in CM-1 patients. The volume of fluid moved each heartbeat, or stroke volume, has shown promise as a new metric to characterize CM-1 malformation in adults, but has been relatively underexplored in the pediatric population. We measured CSF stroke volume in a pediatric CM-1 cohort before and after posterior fossa decompression surgery and in age-matched controls.

Materials and methods: 24 pediatric CM-1 patients (age 9.3 ± 4.5, 7 M, 17 F) underwent posterior fossa decompression surgery to treat CM-1 symptoms and received an MRI pre-operatively and 6 months post-operatively. 8 additional healthy volunteers (age 7.8 ± 5.7, 5 F) were used as control subjects. ECG-gated 2D phase-contrast magnetic resonance (PCMR) scans were acquired in the axial orientation at the foramen magnum (FM). CSF stroke volume was calculated from flow by separately integrating positive and negative flow, then averaging the absolute values.

Results: The CSF stroke volumes in the pre-surgical CM-1 subjects (0.26 ml ± 0.21) were lower than control subjects (0.55 ± 0.2, p < 0.01). Post-surgical stroke volumes in CM-1 subjects (0.44 ± 0.3) were not different than controls (p = 0.18). Pre-surgical stroke volumes were lower than post-surgical stroke volumes across all patients (p = 0.03), and in paired patients who had both pre- and post-surgical scans (p = 0.03). There was no difference in peak velocity pre-surgical and control (p = 0.7) or pre- and post-surgical subjects (p = 0.2). Pre-surgical patients with syrinx (10/15) showed no difference in stroke volume to patients without syrinx (p = 0.6).

Conclusion: Healthy pediatric control subjects had higher CSF stroke flow volume than CM-1 patients. Surgery increased CSF stroke volume in CM-1 patients to values equal to healthy control subjects, and post-surgical stroke volumes were significantly greater than pre-surgical volumes. CSF stroke volume shows potential for use as a flow metric in assessing pediatric CM-1 patients.