Microsurgical anatomy of the anterior commissure with special emphasis on the anterior limb: a comparative white matter fiber microdissection and tractography study.

The anterior commissure (AC) has an anterior and posterior limb. Despite comprehensive information about the posterior limb, there is limited and conflicting information about the anterior limb in the literature. We aimed to show the anatomical relationships of the AC with neighboring structures by using white matter microdissection and magnetic resonance (MR) tractography, primarily on the anterior limb of the AC. Twenty cadaveric human brains and three sheep brains were prepared according to Klingler's method. White matter fiber microdissections were performed. MR tractography was done in 20 specimens. This study defined the body and anterior and posterior limbs of the AC. The anterior limb leaves the body from the inferior side at the level of the anterior perforated substance and olfactory tract. It then courses anteroinferolaterally, curves towards the orbital gyri, and terminates at the olfactory trigone. The posterior limb of the AC divides into rostral (anterolateral) and caudal (posterolateral) parts. The anterior limb was more prominent in sheep than in human brains. This study accurately delineates the anatomy and variations of the anterior limb of the AC in human and sheep brains for the first time in the literature to the best of our knowledge. The anterior limb of the AC is larger in sheep than in humans. An increased importance of olfaction could be the evolutionary explanation for this difference. The MR tractography results shown are unique for this delicate anatomy.