![]() This is why they are susceptible to compression (e.g. CN III palsy with fixed dilated pupil, it is important to recall that pupillary fibers occupy a peripheral location and receive more collateral blood supply that the main trunk of the nerve. Oculomotor nerve damage in this area can produce varied presentations. This space is defined as the area traveled by the oculomotor nerve between the ventral surfaces of the midbrain to the entrance of the cavernous sinus, also known as the interpeduncular fossa. The most common causes include ischemic, hemorrhagic, compressive, infiltrative, traumatic, and rarely, infiltrative and demyelinating process. In addition, although it is known that CN III separates into superior and inferior rami at the superior orbital fissure, sometimes lesions at the fascicles can produce isolated dysfunction of either the superior and inferior division. It is important to remember that lesions can present a combination of these findings depending on the degree of the insult. Lesions at the cerebral peduncle (Weber’s Syndrome) produces ipsilateral 3rd nerve palsy and contralateral hemiplegia. Lesions at the Red Nucleus and superior cerebellar peduncle (Claude Syndrome) presents with ipsilateral 3rd nerve palsy, contralateral ataxia, asynergy and tremor. Lesions at the Red Nucleus (Benedikt's Syndrome) are characterized by ipsilateral 3rd nerve palsy and contralateral involuntary movement. Lesions at the superior cerebellar peduncle ( Nothnagel’s Syndrome) presents with ipsilateral 3rd nerve palsy and cerebellar ataxia. When the lesion is adjacent to the CN III nucleus (midbrain) it can produce several manifestations that have been described according to other neurological manifestations. ![]() The majority of the time it cannot be differentiated from lesion outside of the midbrain. ![]() Lesions at this level can produce complete or incomplete palsies. Lesions of Oculomotor Nerve Fascicles (Leaving the 3rd nerve nucleus) often caused by ischemia, usually from embolic or thrombotic occlusion of small, dorsal perforating branches of the mesencephalic portion of the basilar artery. Patients with damage to the oculomotor nuclear complex need not have ipsilateral pupillary dilation, but when involved, it may indicate dorsal rostral damage. Both levator palpebrae superioris are innervated by one subnucleus (central caudal nucleus) therefore a central caudal nuclear lesion would produce bilateral ptosis. Each of the superior recti (SR) muscles are innervated by the contralateral CN III subnucleus therefore a nuclear CN III palsy would produce paralysis of the contralateral SR. It is divided into subnuclei according to the innervated area. This is explained by the anatomy of the nucleus. The following flowchart represents the anatomic course of cranial nerve III with a designated description of clinical manifestations To understand the pathophysiology of the oculomotor nerve palsy it is essential to know its pathway. In some cases, the precise site of the lesion is clear, whereas in others, the location of the lesion is speculative. The manifestations may depending on the location of the lesion. Risk factors may coincide with the potential underlying etiologies listed above and can include diabetes mellitus, hypertension, vasculitis, trauma, infections, tumor, aneurysm etc. There are many etiologies for oculomotor palsy including a vasculopathic process, trauma, compression (e.g. A partial third nerve palsy may be more common, and can present with variable duction limitation of the affected extraocular muscles and with variable degrees of ptosis and/or pupillary dysfunction. ![]() A complete third nerve palsy presents with complete ptosis, with the eye positioned downward and outward with the inability to adduct, infraduct, or supraduct, as well as a dilated pupil with sluggish reaction. It can be divided into a partial or complete palsy. 1.9 Lesions within the Cavernous Sinus and Superior Orbital FissureĬlinical findings of an acquired third nerve palsy depend on the affected area of the oculomotor nerve pathway.1.7 Lesions of Oculomotor Nerve Fascicles (Leaving the 3rd nerve nucleus).1.6 Lesions of Oculomotor Nucleus (Midbrain).
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