Cerebral venous variations in the region of the third ventricle on PSI. Abbreviations are the same as in Fig 1. A, Type IA: the ASV-ICV junction is located at the venous angle, which lies adjacent to the posterior margin of the foramen of Monro. B, Type IIA (left): the ASV joined the false venous angle, which lies beyond the foramen of Monro. Type IB (right): the ASV joined the mainstem of the ICV posteriorly beyond both the foramen of Monro and the venous angle. C, Type IA (left), type IIB (right): the ASV joined the mainstem of the ICV far beyond both the foramen of Monro and the false venous angle. D, Type III (left): the ASV joined the medial atrial vein and the venous angle is formed. Type IA (right).