Age-related changes in the relative growth of the posterior fossa.

We have established a normative data set for the relative size of the structures of the midline posterior fossa from birth to 90 years old. Data were obtained from morphometric analysis of midsagittal magnetic resonance imaging scans of the brain utilizing a simple image analysis system. There are several significant changes in the size of these structures with an increase in chronologic age. The relative size of the cisterna magna decreases with age. Anterior cerebellar vermal lobules (I through V) appear to grow more rapidly than the rest of the cerebellum. Other, less significant, trends include a decrease in the overall size of the cerebellum, superior posterior vermal lobules (VI and VII) and inferior posterior lobule (VIII) with an increase in age. It is, therefore, necessary to use age-standardized normative data when making morphometric correlations with clinical disorders.