Multi-Dimensional Morphometric and Volumetric Analysis of the Posterior Cranial Fossa to Study Type I Chiari Malformation.

Background: Chiari malformation type I (CM-1) is a complex disorder in which tonsillar herniation through the foramen magnum (FM) manifests with a spectrum of clinical symptoms. This work analyzes morphometric and volumetric characteristics of CM-1 patients.

Methods: With institutional review board approval, we retrospectively reviewed a total of 72 adult CM-1 patients and 26 healthy adult volunteers who underwent volumetric magnetic resonance brain imaging. Clinical data were retrospectively extracted from the electronic medical record. We analyzed multidimensional morphometric and volumetric features within the posterior cranial fossa and correlated these features with syrinx formation and the decision to undergo surgical decompression.

Results: In our study, CM-1 patients had decreased cerebellar (CBL), brainstem, and fourth ventricular volumes but larger tonsillar volume with increased total tonsillar length. CM-1 patients who underwent surgery had significantly more neural tissue within the cross-sectional area of the cisterna magna. Logistic regression demonstrated that combining neural tissue at the FM with CBL and fourth ventricular volumes led to a great degree of correlation with syrinx formation (area under the curve: 0.911).

Conclusions: Our findings suggest that the amount of tissue at the FM correlates with CM-1 patients who underwent decompressive surgery, more so than tonsillar length. Additionally, the combination of neural tissue at the FM, CBL, and fourth ventricular volumes led to a great degree of correlation with syrinx formation. Together, these findings suggest that a global compressive phenomenon within the posterior fossa leads to CM-1 symptomatology and syrinx formation.