he oculomotor nerve is frequently involved with neoplasms involving the petroclival area and the tentorial T notch, as well as by aneurysms involving the internal carotid artery (at the origin of the posterior communicating artery) or the upper basilar artery (especially large or giant aneurysms, and basilar arteryesuperior cerebellar aneurysms). Because of its location in the tentorial notch, oculomotor paralysis is seen in brain herniation syndromes, or after direct trauma. Anatomically, the nerve has 3 distinct areas that it occupies, namely the cisternal segment, the cavernous segment (in the lateral wall of the cavernous sinus), and the orbital segment (in the apex of the orbit). The nerve mainly contains fibers to many of the orbital muscles, but also carries parasympathetic fibers to the pupillary muscle. It is important to note that similar to the facial nerve, many of the muscles controlled by the oculomotor nerve have antagonistic effects (the superior and inferior rectus, for example). This becomes important when one considers the outcome of oculomotor nerve reconstruction.