Introduction: Pediatric Chiari I anomaly is a common incidental finding. There are reports of tonsillar ectopia resolving, but none which follow tonsillar position over regular follow-up intervals. We prospectively followed children with non-operatively managed Chiari I for up to seven years to elucidate the natural history of the dynamics of this condition.

Methods: All children who presented with Chiari I over twelve years were separated prospectively into operative and non-operative groups. Symptomatic patients and patients with syringomyelia underwent suboccipital decompression. Non-operative patients were followed with annual MRI. At each interval, patients were divided into changed and unchanged groups. An alteration in tonsillar descent 2mm or greater was considered a change.

Results: Fifty-two children with non-operatively managed Chiari I were included. Three patients were excluded because they later underwent surgery based on symptoms. No surgeries were performed for radiographic change. Overall, 50% remained stable, 38% reduced, and 12% increased on follow up imaging. Resolution was seen in 12%. Changes were seen during every year of follow up. On average, in any given year 24% of scans showed some form of change. No factors to predict change were identified.

Conclusions: Pediatric Chiari I is not a static entity but rather a dynamic one. Radiographic changes were seen throughout follow-up. Substantially more patients showed reduction in tonsillar descent than increase. Radiographic changes did not correlate with symptom development. Regular imaging of children with Chiari I presenting without a syrinx did not affect any treatment decisions.

Patient Care: Pediatric patients with asymptomatic Chiari I anomalies without syrinx may forgo regular MRI imaging with its associated costs as well as the multiple episodes of general anesthesia needed for younger children to obtain these images.

Learning Objectives: By the conclusion of this presentation, participants should understand that: 1) pediatric Chiari I anomaly is a dynamic condition, 2) changes in tonsillar ectopia do not correlate with symptoms, and 3) routine follow-up imaging alone does not lead to any clinical interventions.

References: 1. Aitken LA, Lindan CE, Sidney S, Gupta N, Barkovich AJ, Sorel M, et al. Chiari type I malformation in a pediatric population. Pediatr Neurol 40(6):449-54, 2009 2. Avellino AM, Britz GW, McDowell JR, Shaw DW, Ellenbogen RG, Roberts TS. Spontaneous resolution of a cervicothoracic syrinx in a child. Case report and review of the literature. Pediatr Neurosurg 30(1):43-6, 1999 3. Avellino AM, Kim DK, Weinberger E, Roberts TS. Resolution of spinal syringes and Chiari I malformation in a child. Case illustration. J Neurosurg 84(4):708, 1996 4. Benglis D Jr, Covington D, Bhatia R, Bhatia S, Elhammady MS, Ragheb J, et al. Outcomes in pediatric patients with Chiari malformation Type I followed up without surgery. J Neurosurg Pediatr 7(4):375-9, 2011 5. Castillo M, Wilson JD. Spontaneous resolution of a Chiari I malformation: MR demonstration. AJNR 16(5):1158-60, 1995 6. Guillen A, Costa JM. Spontaneous resolution of a Chiari I malformation associated syringomyelia in one child. Acta Neurochir 146(2):187-91, 2004 7. Jatavallabhula NS, Armstrong J, Sgouros S, Whitehouse W. Spontaneous resolution of isolated Chiari I malformation. Childs Nerv Syst 22(2):201-3, 2006 8. Martinot A, Hue V, Leclerc F, Vallee L, Closset M, Pruvo JP. Sudden death revealing Chiari type 1 malformation in two children. Intensive Care Med 19(2):73-4, 1993 9. Massimi L, Caldarelli M, Frassanito P, Di Rocco C. Natural history of Chiari type I malformation in children. Neurol Sci 32 Suppl 3:S275-7, 2011 10. Mikulis DJ, Diaz O, Egglin TK, Sanchez R. Variance of the position of the cerebellar tonsils with age: preliminary report. Radiology 183(3):725-8, 1992 11. Miller JH, Limbrick DD, Callen M, Smyth MD. Spontaneous resolution of Chiari malformation Type I in monozygotic twins. J Neurosurg Pediatr 2(5):317-9, 2008 12. Novegno F, Caldarelli M, Massa A, Chieffo D, Massimi L, Pettorini B, et al. The natural history of the Chiari Type I anomaly. J Neurosurg Pediatr 2(3):179-87, 2008 13. Rafia S, Pascual-Castroviejo I. Syringohydromyelia. Report of a case which resolved spontaneously. Rev Neurol 32(7):635-7, 2001 14. Strahle J, Muraszko KM, Kapurch J, Bapuraj JR, Garton HJ, Maher CO. Natural history of Chiari malformation Type I following decision for conservative treatment. J Neurosurg Pediatr 8(2):214-21, 2011 15. Sudo K, Maruo Y, Tashiro K, Terae S, Miyasaka K, Isu T. Syringomyelia with spontaneous resolution. J Neurol Neurosurg Psychiatry 53(5):437-8, 1990. 16. Sun JC, Steinbok P, Cochrane DD. Spontaneous resolution and recurrence of a Chiari I malformation and associated syringomyelia. Case report. J Neurosurg 92(2 Suppl):207-10, 2000. 17. Sun PP, Harrop J, Sutton LN, Younkin D. Complete spontaneous resolution of childhood Chiari I malformation and associated syringomyelia. Pediatrics 107(1):182-4, 2001 18. Tokunaga M, Minami S, Isobe K, Moriya H, Kitahara H, Nakata Y. Natural history of scoliosis in children with syringomyelia. J Bone Joint Surg Br 83(3):371-6, 2001