Is there a relationship between the extent of tonsillar ectopia and the severity of the clinical Chiari syndrome?

Abstract

Chiari 1 malformation is diagnosed if the cerebellar tonsils extend at least 5mm below the opisthion-basion line. To examine the correlation of the extent of tonsillar ectopia with the prevalence and severity of the symptoms associated with the Chiari malformation. Patients (N = 428) were grouped according to the extent of tonsillar ectopia on the mid-sagittal MRI image (group 1, 0-< 3mm; group 2, 3-5mm; group 3, > 5mm). Groups were compared regarding demographics, symptoms, neurological signs, pain score, and response to HADS and sf-36 questionnaires. Results were analyzed using one-way ANOVA, chi-square, and two sample Z test, and Student's t test for pairwise comparison, (statistical significance p < 0.05). A logistic regression analysis was performed to determine the relationship between tonsillar ectopia and the probability of a patient reporting any particular symptom. There were 97,148 and 183 patients in groups 1, 2, and 3 respectively. Groups did not differ with regard to antecedent trauma or female preponderance. Patients in group 1 were more symptomatic than those in groups 2 and 3 with regard to some symptoms, (p = 0.04-p = 0.000). Regression analysis confirmed an inverse relationship between the extent of tonsillar ectopia and the likelihood of many symptoms. The pain score was greatest in group 1, (p = 0.006). Prevalence of objective signs of myelopathy did not differ between groups except for Hoffmann sign which was more prevalent in group 1, (p = 0.034). HADS and sf-36 scores did not differ between groups. The severity of the symptoms associated with the Chiari malformation does not correlate directly with the extent of tonsillar ectopia. The extent of tonsillar ectopia should be re-evaluated as the threshold for diagnosis of Chiari 1 malformation.