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FIG 9. Four components constituting the BVR and the drainage pathways (1–5). The components develop as the telencephalic vein, diencephalic vein, and mesencephalic vein in the 14- to 18-mm embryonic stage and differentiate to the deep telencephalic vein (A), the ventral diencephalic vein (B), and the dorsal diencephalic vein (C). The BVR is formed by the anastomoses between these components and the mesencephalic vein (D) during the 60- to 80- mm embryonic stage (Padget). Each primitive vein (four vessels) has one or more drainage pathways (five routes). The extent of the anastomoses and the drainage pathways result in a huge number of variations.FIG 10. Longitudinal anastomoses of the primitive veins and the drainage routes of the BVR. Five drainage pathways to be considered when the BVR is evaluated. 1: to great vein of Galen, 2: to cavernous sinus or sphenoparietal sinus, 3: to superior petrosal sinus via lateral mesencephalic vein, 4: to superior petrosal sinus via the peduncular vein, 5: to transverse sinus or straight sinus via the tentorium
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