A, The A1, A2, and AComA are exposed above the optic chiasm. The left recurrent arteries arise from the ACA at the level of the AComA and travel laterally above the carotid bifurcation and below the anterior perforated substance. A small frontal branch arises at the same level on the right side. The stump of the right carotid artery has been folded upward and the left downward. B, the chiasm has been reflected downward and the ACA gently elevated to expose the perforating branches that arise from the AComA and pass backward to enter the diencephalon through the region of the lamina terminalis. The AChAs pass around the medial aspect of the uncus. C, The A1s have been removed to expose the recurrent arteries passing laterally below the anterior perforated substance. The left recurrent artery is larger than the right. D, The anterior communicating complex has been folded downward to expose the perforating branches that pass upward and enter the brain through the region of the lamina terminalis. (Images courtesy of AL Rhoton, Jr.)