Authors :
Presenting Author: Kiefer Forseth, MD, PhD – University of California San Diego
Margaret Seaton, BA – University of California San Diego
Vijay Ravindra, MD – University of California San Diego
David Hersh, MD – Connecticut Children’s Hospital
Christopher Conner, MD, PhD – University of Connecticut
Rationale:
Magnetic resonance guided focused ultrasound (MRgFUS) is a non-invasive, localized, non-ionizing technique used clinically in adult patients with brain tumors, movement disorders, and currently under investigation for the treatment of epilepsy. Treatment effect depends on stimulation frequency: low intensity (LIFU) can be used for neuromodulation and blood-brain barrier disruption while high intensity (HIFU) leads to tissue ablation. Pre-operative evaluation includes an assessment of the patient’s skull density ratio (SDR) to determine treatment eligibility. Derived from preclinical studies, low SDR has been shown to hinder temperature rise at the treatment site leading to suboptimal treatment. Theoretical variability in skull density during development has precluded widespread adoption of MRgFUS for children; however, no studies quantify SDR ranges in a large population of pediatric patients. The aim of this study is to generate an age-based atlas of global calvarial density, volume, and SDR in patients aged 0-18 years.
Methods:
Computed tomography of the head (CTH) is routinely obtained during clinical evaluation; scans without abnormalities present an opportunity to study calvarial morphometrics in this sensitive population. We identified 500 pediatric patients with high-resolution CTH. The nasion and bilateral spines of Henle were manually denoted on each scan to define a consistent reference plane that when displaced 2cm superiorly segmented the calvarium. We then simulated 1000 ray traces from the origin to points distributed equally across a hemisphere of radius 14cm. Peaks in density representing the inner and outer cortical tables were then identified along each ray trace. We subsequently derived density, volume, and SDR across the calvarium.
Results:
This methodology robustly identifies density, volume, and SDR across the calvarium – even in very young children with open sutures (no cortical density peak) or without a discrete cancellous layer (detected as a single cortical density peak). We defined the following age categories: < 2 months, 2 months to 2 years, 2 to 7 years, 7 to 14 years, and >14 years. The population density, volume, and SDR distributions were calculated for each age range. While children under 7 had significantly higher SDR than those 14+ (t-test, p< 10-3), those aged 7 to 14 had similar SDR (mean 0.49) to those 14+ (t-test, p=0.301). Skull density reached maturity more quickly – children under 2 had significantly lower peak density (t-test, p< 10-6) while those above 7 had similar peak density (t-test, p=0.322). Open sutures comprised an average of 19.5% of the skull surface in children under 2 months, decreasing to 7.8% by the first year, and further to < 0.01% after the second year.