Chiari 1.5: A lesser known entity

Chiari I Deformity: Beyond 5 mm below the Foramen Magnum

Although originally described as a consecutive series of pathologic changes, Chiari syndrome represents a spectrum of disease divided into two subsets: development deformities of the paraxial mesoderm manifesting after birth (types 0-1.5) and true congenital malformations due to failure of neural tube closure present in utero (types 2-5). Heterogeneity among patients with a Chiari deformity and incomplete understanding of its pathophysiologic characteristics have led to inconsistency in radiologic reporting and difficulty in defining appropriate management strategies tailored to an individual patient's condition. The radiologist is tasked with going beyond the criteria for cerebellar tonsillar herniation to define an individual patient's disease state, determine candidacy for surgery, and assist in selecting the proper surgical approach. In addition, the radiologist must be able to identify conditions that result in cerebellar tonsillar herniation that are not related to Chiari deformity to avoid inappropriate surgery. Last, the radiologist must be able to interpret postoperative imaging examinations to assess for adequacy of treatment and complications. The authors summarize recent literature regarding the pathophysiologic basis of Chiari 1 and related deformities and detail the ideal morphologic and physiologic imaging assessment, focusing on Chiari 1 and related deformities (Chiari 0, 0.5, and 1.5). Also discussed are surgical techniques and "pearls" of postsurgical imaging, including complications that must be recognized. This review provides clarity to a commonly encountered but less understood condition to optimize outcomes for patients with Chiari 1 and related deformities. ©RSNA, 2024 Supplemental material is available for this article. See the invited commentary by Huisman in this issue.

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.