CN 3 anatomy
Nucleus
- Location
- Near the midline at the level of the superior colliculus in the mid-brain.
- Anterior/ventral to sylvian aqueduct separated by periaqueductal gray
- Posterior/Dorsal to Medial longitudinal fasciculus
- Oculomotor nuclear complex
- Made of
- 1 unpaired columns
- Edinger westphal nuclei
- Most rostral
- Contain parasympathetic neurons that mediate constriction of the pupil.
- Ipsilateral innervation
- Sub nucleus of the levator palpebrae superioris (Caudal central nucleus)
- Most caudal
- Bilateral innervation.
- 4 paired columns
- Medial: superior rectus muscle
- Sends axon to contralateral eye by traveling thru the contralateral superior rectus subnucleus
- Disruptive lesion in one superior rectus subnucleus results in bilateral denervation of superior recti
- Laterally
- Dorsal: inferior rectus
- Ipsilateral innervation
- Intermediate: inferior oblique
- Ipsilateral innervation
- Ventral: medial rectus
- Ipsilateral innervation
The motor neuron pools in the nucleus are shown in frontal sections through anterior (B) and posterior (C) parts of the nucleus. The superior rectus is the only one that crosses over
Travel thorough the mid brain
- Thorough
- MLF
- Red nucleus
- Exit medial to the cerebral peduncle
- Nerve exit the midbrain and passes between
- Superior cerebellar artery and
- Posterior cerebral artery
Cisternal
- Courses forward medial (very close) to the uncus of temporal lobe
- It is related laterally to the inferior portion of the apex of the uncus;
- Just before piercing the roof of the cavernous sinus, It is located below the anterior segment of the uncus
- Pierces through the dura just lateral to posterior clinoid process
Cavernous
- Enters lateral wall of cavernous sinus
Enters superior orbital fissure and oculomotor foramen in the annular tendon
- Branches into
- Superior division:
- Superior rectus
- Levator palpebrae superioris muscles
- Inferior division
- Inferior rectus muscles
- Inferior oblique muscles
- Medial rectus muscles
- Parasympathetic fibers that mediate pupillary constriction and accommodation.
- The oculomotor nerve gives rise to the parasympathetic motor root to the ciliary ganglion that lies lateral to the optic nerve.
- The abducens nerve passes through the oculomotor foramen and enters the medial surface of the lateral rectus muscle.
CN3 Reflex
- Light reflex
- Pathway
- Light → retina → optic nerve → optic chiasm → optic tract → superior brachium → pretectal area of mid brain → posterior commissure → Edinger-Westphal nucleus → CN 3 → Ciliary ganglion → short ciliary nerves → pupil constriction
- Does not go up to the cortex
- Near far accommodation reflex
- Procedure
- Ask patient to look far and then look near
- Results
- Convergence
- Pupillary contraction
- Increased convexity of lens to increase refractive pathway
- Pathway
- Light → retina → optic nerve → optic chiasm → optic tract → Lateral geniculate nucleus → optic radiation → primary visual cortex (striate/calcarine cortex) → extra-striatal (association visual cortex) → prefrontal cortex → Edinger Westphal sub-nucleus + oculomotor nucleus → CN3 → pupillary muscle + papillary muscle + medial rectus
- Disease
- Pre-tectal area damaged causing light accomodation dissociation (light don't work)
- Argyll Robertson pupil (prostitute pupil)
- Parinauds syndrome
CN3 palsy
- Clinical features
- Ptosis
- Mydriasis
- Out and down (exotropic and hypotropic)
- CN4 and CN6 working only
CN3 Lesion localisation
Lesions affecting the third nerve nucleus
- General
- Rare.
- 3 major patterns of deficits are associated with it
- Complete third nerve palsy (including ptosis) on the ipsilateral side, plus ptosis and superior rectus palsy on and the opposite side
- The whole oculomotor nucleus complex is affected
- Bilateral ptosis with normal extraocular movements
- The caudal central nucleus is affected
- Bilateral third nerve palsy with lid sparing.
- The caudal central nucleus is not affected
- Midbrain corectopia
- Segmental innervation of the pupil by the Edinger-Westphal nucleus.
- When rostral midbrain where the Edinger-Westphal nucleus is located is infarcted or has blood can lead to paralysis of some of the dilator muscle, central inhibition of sphincter tone resulted in an oval and eccentric pupil.
- Almost impossible to have unilateral superior rectus, levator palpebral superiors and pupillary sphincter malfunction, they will have bilateral signs seeing how close they are located.
- Medial rectus lie in all three areas of the lateral column so if there is an isolated medial rectus problem it is unlikely due to a nuclear lesion
- Oculomotor nucleus:
- Presentation
- Ipsilateral complete CN III palsy;
- Contralateral ptosis and superior rectus paresis
- Oculomotor subnucleus:
- Isolated muscle palsy (e.g., inferior rectus);
- Isolated levator subnucleus
- Isolated bilateral ptosis
Lesions affecting the third nerve fasciculus
- Isolated fascicle
- Partial or complete isolated CN III palsy with or without pupil involvement;
- Paramedian mesencephalon:
- Plus–minus syndrome (ipsilateral ptosis and contralateral eyelid retraction)
- Fascicle, red nucleus, superior cerebellar peduncle:
- Ipsilateral CN III palsy with contralateral ataxia and tremor (Claude)
- Claude syndrome
- Damaged to the
- CN3 fascicle
- Red nucleus
- Sup. Cerebellar peduncle
- Presentation
- Contralateral ataxia
- Cerebellar tremor
- Fascicle /cerebral peduncle:
- Weber syndrome (more anterior injury than claude syndrome)
- Damaged to
- Cerebral peduncle
- CN3 fascicle
- Presentation
- Contralateral paresis
- (Ipsilateral cerebral peduncle (corticospinal and corticobulbar tracts) will dessucitate later).
- Ipsilateral Oculomotor palsy
- Fascicle/red nucleus/substantia nigra:
- Benedikt syndrome
- Damaged to
- CN3 fascicle
- Red nucleus + substantia nigra
- Cerebral peduncle
- Presentation
- Ipsilateral Oculomotor palsy
- Contralateral choreiform movements/tremor
- Contalateral hemiparesis
- Tectal plate/superior cerebellar peduncle:
- Nothnagel's syndrome:
- Posterior thalmoperforating arteries: a direct perforating artery occlusion
- Due to tumour and stroke
- Presentation
- Cerebellar ataxia
- Ipsilateral oculomotor nerve paresis
Lesions affecting the third nerve in the subarachnoid space
- Oculomotor nerve:
- Complete CN III palsy with or without other cranial nerve involvement; superior or inferior division palsy
- Involvement of the third nerve in the subarachnoid space results in symmetric involvement of all divisions of the third nerve
- Surgical 3rd nerve palsy
- Due to PCOM Aneurysm
- Whole nerve affected → pupil non sparing
- Painful
- Medical 3rd nerve palsy
- Due to
- Ischaemic lesioning
- Diabetes
- Blood supply of the nerve comes from out to in
- Parasympathetic nerve coats the outside of the 3rd nerve so it is spared → pupil sparing
- Motor nerves are more central so it is affected → Down and out pupil
- Painless
Lesions affecting the third nerve in the cavernous sinus
- General
- Usually the third nerve palsy is of the pupil-sparing type because compressive lesions in the cavernous sinus preferentially involve only the superior division of the oculomotor nerve, which contains no pupillomotor fibers.
- The fronto-orbital pain that is often associated with a cavernous sinus lesion may be the result of the fact that sensory fibers from the ophthalmic division of the trigeminal nerve join the oculomotor nerve within the lateral wall of the cavernous sinus.
- Cavernous sinus lesion/syndrome:
- Painful or painless CN III palsy;
- With or without palsies of CN IV, V1, and V2;
- Mixed CNIII palsy and Horner's gives a small or mid-dilated poorly reactive pupil.
- Primary aberrant CN III regeneration
- Lid malposition (ptosis or lid edema)
- Tolosa Hunt syndrome
- Cavernous sinus inflammation + orbital apex
- Like cavernous sinus syndrome but
- Always painful and V1>V2 pain
Lesions affecting the third nerve in the superior orbital fissure
- General
- Hard to differentiate vs cavernous sinus lesion
- Lesions in superior orbital fissure are more likely to be associated with proptosis.
- Superior orbital fissure lesion:
- CN III palsy with or without palsies of CN IV, VI, V1; often with proptosis
- Like Cavernous sinus syndrome
- Never have CNV3 or CNII involvement
Lesion affecting the third nerve in the orbit
- General
- Lesions that involve the third nerve in the orbit are frequently associated with other ocular motor signs as well as optic atrophy and proptosis.
- Isolated involvement of either the superior or inferior division of the oculomotor nerve is most commonly associated with lesions in the orbit.
- Oculomotor nerve; superior or inferior branch lesion:
- CN III palsy; superior or inferior CN III branch palsy
- Optic nerve; orbital structures:
- Visual loss; proptosis; swelling of lids; chemosis
- Orbital apex syndrome
- Optic nerve (RAPD/visual loss)
- CN Ill, IV, VI
- Proptosis common
- CNV1
- Hypoesthesia in ophthalmic division
- Marcus Gunn Phenomenon (Marcus Gunn Jaw winking syndrome (MGJWS)
- Seen more in CN 3 than CN7
- Regen motor fibers miss their target instead innervates new nerves
- Example of diseases associated with it
- Blinking causes Twitching of the left side of the mouth
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