Characterizing symptom presentation in Chiari malformation type-1 in two subpopulations of pediatric patients who underwent decompression.

Background: Chiari malformation type-1 (CM1), or displacement of the cerebellar tonsils below the foramen magnum, causes symptoms through brainstem compression or obstruction of the flow of cerebrospinal fluid. Presenting symptoms have been shown to differ in children and adults. Pediatric patients at different stages of development may present differently; thus, we investigated clinical differences in symptom presentation in children younger and older than 9 years old. Methods: Pediatric patients (0-18 years old) who underwent decompression for CM1 at our institution between 2010 and 2023 were retrospectively reviewed for demographic, clinical, radiographic, surgical, and follow-up data. The Chicago Chiari Outcome Scale (CCOS) was used to quantify treatment outcome. Results: 232 pediatric patients were included in this analysis. An expectation-maximizing algorithm generated a Gaussian mixture model which identified a bimodal distribution of ages at which our patients underwent surgery, possibly representing two distinct pediatric populations with CM1. K-means analysis set to two clusters found that the trough of the distribution was 9 years old. 100 patients were <9 (median = 5.1, group A) and 132 were ≥9 (median = 14.6, group B). Significantly more males had surgery in group A (62% males, 38% females) than group B (44% males, 56% females) ( Conclusion: We found two distinct age groups of symptomatic CM1 patients who presented for surgery. Patients in the younger cohort were less likely to present with headache or syrinx and had greater improvement in their nonpain symptoms after surgery.