Variations of the position of the cerebellar tonsil in idiopathic scoliotic adolescents with a cobb angle >40 degrees: a magnetic resonance imaging study.

STUDY
DESIGN: A retrospective study was performed through measurements on MRI images in adolescent idiopathic scoliosis (AIS) patients and age-matched adolescents.
OBJECTIVES: To investigate the position of the cerebellar tonsil in AIS patients with a Cobb angle >40 degrees in comparison with age-matched healthy adolescents and to determine the relationships of the tonsil position with age, sex, curve severity, and curve patterns. SUMMARY OF BACKGROUND DATA: There have been increasing evidences implying that AIS patients may present with subtle or subclinical neurologic dysfunction and a higher incidence of tonsillar ectopia was documented in AIS patients. However, the tonsil position has not been clearly addressed in AIS patients with a severe curve.
METHODS: According to the method described by Aboulezz et al, measurements of the tonsil position relative to the magnum foramen on magnetic resonance images were performed in 203 AIS patients with a Cobb angle >40 degrees and 86 age-matched healthy adolescents. The inferior displacement of the cerebellar tonsil with an extent within 5 mm was defined as tonsillar ectopia when it located below the magnum foramen. On the basis of measurement results, the incidence of tonsillar ectopia was determined in both AIS and control groups. The associations of tonsillar ectopia with curve severity and curve patterns for AIS patients and the relationships of the tonsil positions with age and gender in all subjects were analyzed.
RESULTS: In AIS patients and healthy controls, the median position of the cerebellar tonsil was 0.8 and 2.9 mm above the magnum foramen, respectively. The incidence of tonsillar ectopia (0-4.8 mm below the magnum foramen) in AIS was found to be significantly higher than healthy adolescents (range 0-1.8 mm vs. 0-4.8 mm below the magnum foramen; ratio 34.5% vs. 5.8%; P < 0.01). No significant correlations were found between the position of the cerebellar tonsil with age or gender in AIS and control subjects. It was shown the position of the cerebellar tonsil was not significantly different among AIS patients with different curve severity. However, it was noted that there was a highest incidence (62.5%) of tonsillar ectopia in atypical scoliotic cases with a double thoracic curve. Additionally, a significantly higher incidence of tonsillar ectopia was found in patients with thoracic or thoracolumbar curves when compared with those with lumbar curves (37.4% vs. 21.6%, P = 0.049).
CONCLUSION: Tonsillar ectopia with the extent >2 mm in AIS patients should be regarded as abnormal. AIS patients had a lower tonsil position and a higher prevalence of tonsillar ectopia than controls, and tonsillar ectopia was found to be associated with curve patterns. It is suggested that a lower position of the cerebellar tonsil might be associated with the etiopathogenesis of AIS and might contribute to subclinical neurologic dysfunction in AIS patients.