Fig. 1

Measurements of infratentorial structures. Anteroposterior diameter of the pons was measured at the level of the opening of the sella turcica (a). Transverse diameter of the pons was measured as the distance between two points perpendicular to the midline along the tangent lateral to the pons (b). Midbrain anteroposterior diameter was measured at a midline level on a sagittal section (c). Cerebellar height was defined as the distance between the apex of the anterior lobe of the cerebellum and the apex of the cerebellar flocculus (H-I line was perpendicular to the AC-PC line) (d)