Fig. 14.2 Coronal CISS image: cisternal segment of CN III lies in the “oculomotor triangle” defined superiorly by the posterior cerebral artery and inferiorly by the superior cerebellar artery
14.2 Function
Motor function (GSE): controls the superior rectus, medial rectus, inferior rectus, levator palpebrae, and inferior oblique muscles. The medial rectus muscle allows for adduction of the eye, the inferior rectus muscle moves the eyeball downward, the superior rectus moves the eyeball upward, the inferior oblique moves it upward and outward, and levator palpebrae moves the eyelid upward.
Parasympathetic function (GVE): activation leads to pupillary constriction and lens accommodation.
14.3 Pathology
Individual symptoms: Damage to the oculomotor nerve results in the following symptoms depending on location:
Nuclear lesion: Isolated nuclear lesions are extremely rare. Ipsilateral lesion will cause ipsilateral oculomotor palsy and bilateral paralysis of the superior recti and the levator palpebrae (both have a bilateral innervation), resulting in incomplete ptosis bilaterally.
Cisternal lesions: Lesions to the cisternal segment will cause only ipsilateral symptoms (Figs. 14.3 and 14.4). Uncal herniation or compression by a PCOM or SCA aneurysm will inhibit pupillary constriction in the ipsilateral eye (mydriasis) without necessarily affecting ocular movement:
Anisocoria: asymmetry of pupils (fixed mydriatic pupil on the affected side).
Extraocular muscle palsy: unopposed muscle tension by the superior oblique and lateral rectus results in down- and outpositioning of the globe.
Cavernous sinus lesions: Due to lateral extension of a pituitary mass into the cavernous sinus, skull base meningioma, epidermoid cyst, arachnoid cyst, schwannoma, or neurofibroma that compresses CN III in its cisternal or intradural segment. Other lesions include carotid-cavernous sinus fistula, cavernous sinus thrombosis, carotid artery aneurysm, and meningitis [5].
Superior orbital fissure lesions: Most pathology results in similar deficits as lesions in the cavernous sinus. These include hypertrophic idiopathic inflammatory lesions (pseudotumor); bony lesions such as fibrous dysplasia, trauma, and osseous metastasis may also affect contents of the superior orbital fissure (CN III, IV, V1, and VI and superior ophthalmic vein).Related posts:
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