Cranial Versus Cervical Spine Magnetic Resonance Imaging in Adult Chiari Malformation Type I Diagnostics: Is There a Difference in Tonsil Ectopia Length?

BACKGROUND: Chiari malformation type 1 (CM-1) diagnosis is based on measurement of the cerebellar tonsils on cranial or cervical spine magnetic resonance imaging (MRI). However, imaging parameters of cranial and cervical spine MRI could differ because spine MRI has greater resolution. METHODS: We conducted a retrospective chart review of 161 patients of a single neurosurgeon for adult CM-I consultation between February 2006 and March 2019. Patients were selected based on receiving both cranial and cervical spine MRI within a month of each other to determine tonsillar ectopia length for CM-1. Ectopias were measured to determine if differences in values were statistically significant. RESULTS: From the 161 total patients, 81 had cranial and cervical spine MRI for a total of 162 tonsil ectopia measurements (81 cranial and 81 spinal). Average ectopia length on a cranial MRI was 9.1 mm (±5.2 mm); average ectopia length on a spinal MRI was 8.9 mm (±5.3 mm). Average cranial and spinal MRI values were found to be <1 standard deviation apart. Two-tailed, nonequal variances t test determined that differences between the cranial and spinal ectopia measurements were insignificant (P = 0.2403). CONCLUSIONS: This study confirmed that the added resolution offered by spine MRI did not make better or more refined measurements over cranial MRI that could lead to measurement differences, which can instead be attributed to chance. Cranial and cervical spine MRI can be used to determine the degree of the tonsil ectopia.