Redefining the magnetic resonance imaging reference level for the cerebellar tonsil: a study of 170 adolescents with normal versus XXXX .

@entity1984 @entity1 @entity3976 @entity75 @entity1645 @entity1635 @entity2112
STUDY DESIGN: Magnetic resonance imaging (MRI) was used to compare quantitatively the position of the cerebellar tonsil in neurologically normal adolescents with that in @entity2112 ( @entity1984 ) @entity1 and age-matched healthy controls. OBJECTIVES: To redefine the normal reference level of the cerebellar tonsil in healthy adolescents and to compare the differences in tonsillar level with @entity1984 of different severities. SUMMARY OF BACKGROUND DATA: Asymptomatic @entity1645 has been reported not infrequently in @entity1 and adolescents with @entity1984 . The @entity3976 and its variations with sex, age, and curve severities have not been clarified. METHODS: Sagittal MRI of hindbrain was performed on 170 adolescents, including 117 @entity1 with @entity1984 and 53 age-matched healthy controls. RESULTS: The cerebellar tonsillar tip in healthy @entity1 was found at an average of 2.8 mm above the basion-opisthion reference line (BO line) (range, 0-10.5 mm), in contrast to the finding that 17.9% of the @entity1984 @entity1 had tonsillar tip below the BO line. The position of tonsil in the @entity1984 group was lower than that in the healthy controls (P < 0.05), and the differences also increased with the severity of the curve (P = 0.027). CONCLUSIONS: Using the current MRI reference standards, the incidence of @entity3976 could be significantly underestimated. According to our experience, any @entity75 of a tonsil below the BO line in adolescents should be regarded as abnormal. @entity1635 could be an important manifestation of @entity3976 .
