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Unexpected Progression of Tonsillar Herniation in Two Pediatric Cases with Chiari Malformation Type I and Review of the Literature

Background: Chiari malformation type 1 (CM-1) is a generally congenital, rarely acquired disease characterized with 5 mm or more displacement of cerebellar tonsils through foramen magnum. Methods: Here, we report about 2 patients with CM-1 progressed in the degree of tonsillar herniation from our clinic, whereas increasing in prolapse of tonsillar herniation after diagnosis is extremely uncommon. Results: The first patient aged 17 years was diagnosed with CM-1 in 2009 and was operated due to progression of 5 mm radiologically and worsening symptoms in 2014. The second 5-month-old patient initially showed just low-settled tonsillar localization at the borderline, then it descended by 2 cm when the patient reached 3 years of age, yet could not be operated because of parents’ objection. Conclusion: Due to lack of reports on increasing tonsillar descent in the literature, these case reports will contribute to natural history and management of CM-1.