ObjectiveTo investigate the effects of gender and age on the posterior cranial fossa linear volume and cerebellar tonsil position in normal populations.MethodsA total of 180 normal adults who underwent cervical MRI examination at the physical examination center were selected, including 90 males and 90 females; the age ranged from 20 to 79 years, with an average of 50.4 years. The posterior cranial fossa linear volume and cerebellar tonsil position were measured by two spine surgeons on the mid-sagittal plane of the cervical MRI T2-weighted image. The posterior cranial fossa linear volume included the length of clivus (AB), anteroposterior diameter of foramen magnum (BC), length of supraocciput (CD), anteroposterior diameter of posterior fossa (DA), posterior fossa height (BE), and clivus angle (∠α). The index of the cerebellar tonsil position was the distance from the lower edge of the cerebellar tonsil to the baseline (MN). The differences of each indicators between males and females were compared, and the correlations between age and each indicators were analyzed.ResultsThe posterior fossa cranial linear volume AB, BC, CD, BE, and ∠α in males were significantly larger than those in females (P<0.05); DA in males was larger than that in females, but showing no significant difference (t=1.978, P=0.050). The cerebellar tonsil position (MN) in females was higher than that in males, but showing no significant difference (t=0.526, P=0.600). Correlation analysis showed that age was negatively correlated with AB, BC, CD, DA, BE, ∠α, and MN (r=−0.375, P=0.001; r=−0.417, P=0.001; r=−0.046, P=0.001; r=−0.244, P=0.001; r=−0.326, P=0.001; r=−0.320, P=0.001; r=−0.334, P=0.001).ConclusionThe posterior cranial fossa linear volume of normal adults is significantly larger in males than in females; the posterior cranial fossa linear volume and the cerebellar tonsil position may have a decreasing process of age-related degeneration.