Table 1. Comparison of the Three Routes Mentioned.

	Supracerebellar Infratentorial	Occipital Transtentorial	Parietal Interhemispheric
Average distance	53.31 mm	80.13 mm	103.77 mm
Standard deviation	21.46 mm	3.82 mm	10.98 mm
Exposure length	Aqueduct to superior part of the fourth ventricle	Aqueduct to facial colliculus	Aqueduct to foramen Magendie
Splenium cut	No	No	Yes
Tentorial cut	No	Yes	No

Calculated in terms of distance from the surface to the fourth ventricle, the standard deviation of these distances, the amount of exposure gained, with every route, the need to cut the splenium part of the corpus callosum and whether there is a need for a tentorial cut.