A middle rectal artery arising from the lateral sacral artery (MRAls) in the right pelvis of a 99-year-old male was observed. Although variations of the origin of the middle rectal artery have been reported on many occasions, there are few descriptions of the trajectory in the literature. In our case, the MRAls branched from the lateral sacral artery on the sacral surface close to the third sacral sympathetic ganglion and immediately penetrated the third sacral splanchnic nerve and the parasympathetic pelvic splanchnic nerve from the ventral ramus of the forth sacral nerve. The MRAls entered in the lateral wall of the rectal ampulla without giving off a prostatic branch. Preservation of the pelvic autonomic nerves are crucial in rectal cancer excision to preserve the autonomic functions. The close topography of the MRAls to the origin of the fine autonomic nerves should be noted.
Keywords: Arterial variation; Autonomic nerves; Lateral sacral artery; Middle rectal artery; Pelvic plexus.