 Once the suboccipital bone was exposed under the foramen magnum, the high speed drill was used to thin out the suboccipital bone and the craniectomy carried out with Leksell and insertion with Kerrison punches down to the rim of the foramen magnum as well as laterally to the edge of the sigmoid sinus and superiorly to the edge of the transverse sinus. 
Once the suboccipital bone was exposed under the foramen magnum , the high speed drill was used to thin out the suboccipital bone and the craniectomy carried out with Leksell and insertion with Kerrison punches down to the rim of the foramen magnum as well as laterally to the edge of the sigmoid sinus and superiorly to the edge of the transverse sinus .