Central (Nuclear) 3rd Nerve Palsies

Shown here are two patients with left sided midbrain pathology (hemorrhage and ischemia) which caused damage to the 3rd nucleus. Both of the patients have ipsilateral mydriasis, adduction, supra- and infraduction paresis. Ipsilateral>contralateral ptosis is also present, and localizes to the central caudal nucleus. Additionally, both patients have supraduction paresis in the contralateral right eye as well. This is because the fascicles destined for the right superior rectus (SR) muscle originates in the opposite left SR subnucleus - i.e., along with the 4th nerve, the SR fascicles are the only other cranial nerve to decussate. Interesting, in both of these patients there's also infraduction paresis in the contralesional (right) eye, and because there's no clear right 3rd nerve palsy, this is probably suggestive of additional interstitial nucleus of Cajal and/or rostral interstitial MLF damage (and INC or riMLF damage could also be contributing to supraduction deficits as well). In the second patient, there was also mainly torsional nystagmus (beating towards the right ear, not seen in the left eye likely due to significant ophthalmoparesis in this eye) seen in the right eye. A unilateral riMLF lesion can cause contralesional torsional nystagmus while a unilateral INC lesion can cause ipsilesional torsional nystagmus - in her case, given the left sided midbrain stroke, the assumption was that her torsional nystagmus (towards the right ear) was related to additional damage involving the left riMLF.