The pathogenesis of Chiari I malformation and syringomyelia.

OBJECTIVE: The pathogeneses of Chiari malformation type I and syringomyelia are incompletely understood. In this article, the authors attempt to review the current theories on the pathogeneses of Chiari I malformation and syringomyelia. METHODS: A literature review for articles pertaining to Chiari I malformation or syringomyelia before August 2010 was conducted; in addition, the author's own experience in treating Chiari I malformation and syringomyelia is included. RESULTS: Chiari I malformation has been defined radiographically as cerebellar tonsillar herniation or ectopia 5 mm or greater below the foramen magnum. By this narrow definition, Chiari I malformation (i.e. cerebellar tonsillar herniation or ectopia 5 mm or greater below the foramen magnum) likely encompasses a heterogeneous grouping of disorders caused by different mechanisms. Molecular and genetic studies have been helpful in furthering our understanding of Chiari I malformation. CONCLUSION: A review of the pathogeneses of Chiari I malformation and syringomyelia is reported.

National Institutes of Health Chiari Research Conference: state of the research and new directions.

OBJECTIVE: To establish the current Chiari knowledge base and develop recommendations for future research. METHODS: Chiari malformation: state of the research and new directions was a two-day, National Institutes of Health sponsored conference. The agenda included review presentations and working groups tasked with developing specific, achievable research recommendations. Content for both the review presentations and working groups was divided into six areas: pathophysiology, symptoms and diagnosis, engineering and imaging analysis, treatment, pediatric issues, and related conditions. RESULTS: The articles in this issue represent the knowledge base that was developed at the conference, plus subsequent literature reviews. There are significant gaps in the understanding of Chiari malformation, including a clinically relevant definition of Chiari, confusing terminology, subjective diagnostic criteria, and a well-accepted standard of care. These knowledge gaps are not surprising given the relative lack of Chiari research compared to similar neurological conditions and the preponderance of case reports in the published Chiari literature. The lack of understanding, and research, regarding Chiari translates directly into negative patient experiences and outcomes. CONCLUSIONS: Implementation of the recommendations developed at the conference would not only further expand the current understanding of the condition, but would likely have a significant, positive impact on patient experiences and outcomes.

Posterior fossa measurements in patients with and without Chiari I malformation.

PURPOSE: To determine if there is a correlation between cerebellar tonsillar descent in patients with and without Chiari I malformation and three skull morphometric measurements: clivus length, anteroposterior diameter of the foramen magnum, and Boogard's angle. METHODS: Cerebellar tonsillar descent, clivus length, anteroposterior diameter of the foramen magnum, and Boogard's angle were measured in mid-sagittal T1-weighted magnetic resonance images of 188 patients. The study included 81 patients with Chiari I malformations (CMI). Without identifiable pathology, 107 patients served as a comparison group. Two-sample t-tests were used to assess for significance. A Pearson correlation matrix was constructed to assess the strength of linear dependence between measured parameters for the study population. RESULTS: A negative correlation was found between tonsillar herniation and clivus length (r = -0.30, P < 0.001), while a positive correlation was found between tonsillar herniation and foramen magnum size (r = 0.15, P = 0.0431), and Boogard's angle (r = 0.23, P = 0.0014). Clivus length was shorter (P = 0.0009) in CMI patients (4.02 cm ± 0.45) than comparison patients (4.23 cm ± 0.42). In addition, the anteroposterior diameter of the foramen magnum was wider (P = 0.0412) (3.74 cm ± 0.40 compared to 3.63 ± 0.30) and Boogard's angle was larger (P = 0.0079) (123.58 degrees ± 8.27 compared to 120.62 degrees ± 6.79) with CMI. CONCLUSION: A greater degree of cerebellar tonsillar herniation is associated with a shorter clivus length, a wider anteroposterior diameter of foramen magnum, and a wider Boogard's angle.

Posterior fossa morphometry in symptomatic pediatric and adult Chiari I malformation.

The linear dimensions and volume of the posterior fossa, and the length of the supra-occiput and the clivus in children with Chiari I malformations (CMI) were studied. A statistical relationship between patient demographics, radiological features, posterior fossa and occipital bone morphometry in the study and control groups was investigated. The results of 21 pediatric patients was compared to those of a matched control group. The posterior fossa volume (PFV) of an adult CMI group was also studied. Linear measurements were used to calculate the length of the occipital bone, spherical PFV and intracranial volume (ICV) using pre-operative MRI and CT scans. A PFV to ICV ratio was obtained to standardize the comparison. The volumetric measurement in the pediatric study group was also compared to the adult CMI group. The antero-posterior dimension, width, and volume of the posterior fossa and the PFV to ICV ratio in pediatric CMI patients was significantly lower than in the control group (p<0.05). There was no statistical difference in the length of the clivus and the supra-occiput between the two pediatric groups. The difference in the PFV to ICV ratio between pediatric and adult CMI patients was not statistically significant. Thus, the authors provide a simple, yet accurate, and reproducible method of comparison of posterior fossa volume in patients with CMI in different age groups, based on linear measurements. There is no significant difference between the length of the occipital bone at the base of the skull in pediatric CMI patients and the normal pediatric population. Development of the clivus due to late fusion of the sphenoid and occipital synchondroses in the second decade could result in manifestation of the disease in adulthood in CMI patients who were asymptomatic as children.