fig 2.

A and B, Axial MR source images through the midbrain of a 27-year-old male volunteer obtained using the 3D-CISS sequence (12.3/5.9/1) with a distance of 1.32 mm between slices and displayed from caudal (A) to cranial (B). The PComA and AChA can be identified bilaterally. The right AChA (B, straight arrow) is visible where it originates from the posterior wall of the internal carotid artery distal to the origin of the PComA (A, curved arrow). On the left side, the PComA and the cisternal segment of the AChA can be seen (straight arrow, A and B). The AChA is located lateral to the PComA and has a slightly smaller diameter