Introduction: Prior attempts to define normal cerebellar tonsillar position have been limited to a diverse population including adults. There have been no studies targeting the pediatric population, especially Indian children. The aim of this study is to quantify the position of caudal-most location of tip of cerebellar tonsils.

Materials and Methods: MRI studies of 210 consecutive patients ages 0 to 16 years were analysed for location of tonsillar position. Patients with anomalies or mass lesions of the posterior fossa were excluded. The lowest tonsillar position in relation to the basion-ophisthion line was measured. Patients with imaging findings of posterior fossa abnormalities or mass lesions were excluded. A second radiologist independently evaluated 30% of the MRI studies (n = 64) for correlation.

Results: Of the 210 patients, 85 were females. The mean tonsillar height measures 2.76 mm above the basion- ophisthion line with a range from 7.5 mm above to 3.9 mm below the line. The mean values among males was 2.74 mm above and females was 2.8 mms above base line. The correlation coefficient of the two radiologists was 0.88 (strong positive linear correlation). Scatter plots and histograms were created.

Conclusions: Cerebellar tonsillar position follows an essential normal distribution in the pediatric population with values as described above.