No significant difference between chiari malformation type 1.5 and type I

- The clinical and imaging difference between CM 1.5 and CMI is unclear.
- 27 CM 1.5 and 115 CM I adult patients who underwent posterior fossa decompression were evaluated.
- Age at diagnosis was significantly younger in CM 1.5 group than CMI group.
- The degree of tonsillar herniation was more severe in CM 1.5 group than CMI group.
- Other clinical and imaging features and surgical outcomes were similar.

ObjectiveChiari malformation Type 1.5 (CM 1.5) was defined as the association of Chiari malformation Type I (CM I) and brainstem herniation. The objective was to demonstrate the difference of clinical features and surgical outcomes between CM 1.5 and CM I.Patients and methodsAll CM 1.5 and CM I adult patients who underwent posterior fossa decompression with duraplasty at our institution between 2006 and 2010 were retrospectively reviewed. Clinical characteristics, imaging features, and long-term outcomes were compared between CM 1.5 and CM I patients.ResultsA total of 142 adult patients were enrolled, including 27 CM 1.5 and 115 CM I patients. The average follow-up period was 102 months. Age at diagnosis was significantly younger in CM 1.5 group than CM I group (p = 0.039). And the degree of tonsillar herniation was significantly more severe in CM 1.5 group than CM I group (p < 0.001). There was no significant difference in other clinical and imaging characteristics. Moreover, improvement of symptoms was observed in 21 CM 1.5 patients (77.8%) and 94 CM I patients (81.7%), and no significant difference was detected (p = 0.637). There was no significant difference in the resolution of syringomyelia between CM 1.5 (72.7%) and CM I (76.5%) patients, either (p = 0. 710).ConclusionsAlthough CM 1.5 patients presented with brainstem herniation and more severe tonsillar herniation, other clinical and imaging features and surgical outcomes were similar with CM I patients. We think CM 1.5 is just a subtype of CM I, rather than a unique type of Chiari malformations.