CNIII Palsy

Question 1

Where does the CNIII originate from?

Answer 1

Oculomotor Nucleus at the midbrain of the brainstem and emerges from the anterior aspect of the midbrain

Question 2

How does CNIII pass after leaving the anterior aspect of the midbrain?

Answer 2

Then passes inferiorly to the posterior cerebral artery and superiorly to the superior cerebellar artery. It pierces the dura mater and then enters the lateral aspect of the cavernous sinus.

Question 3

What is the course of CNIII from the cavernous sinus?

Answer 3

In the cavernous sinus it receives sympathetic branches from the internal carotid plexus that travel within the sheath of the oculomotor nerve. It leaves via the superior orbital fissure and divides into superior and inferior branches.

Question 4

What is involved in the superior branch of CNIII?

Answer 4

Superior – superior rectus and LPS. Sympathetic fibres run with this to innervate the superior tarsal muscle

Question 5

What fibres run with the superior branch of CNIII and what do they innervate?

Answer 5

Sympathetic fibres run with this to innervate the superior tarsal muscle

Question 6

What is included in the inferior branch of CNIII?

Answer 6

Inferior – Inferior rectus, medial rectus and inferior oblique. Supplies pre-ganglionic parasympathetic fibres to the ciliary ganglion that innervates the sphincter pupillae and ciliary muscles.

Question 7

What are the common aetiologies of CNIII palsy?

Answer 7

• Raised IOP that compressed the nerve against the temporal bone
• Posterior communicating artery aneurysm
• Cavernous sinus infection or trauma
• Diabetes, MS, myasthenia gravis and giant cell arteritis

Question 8

In what type of CNIII palsy are the majority of cases idiopathic?

Answer 8

Congenital CNIII palsies

Question 9

What is the aetiology of congenital CNIII palsy?

Answer 9

There is some evidence of a familial tendency to the condition, particularly to a partial palsy involving the superior division of the nerve with an autosomal recessive inheritance. The condition can also result from aplasia or hypoplasia of one or more of the muscles supplied by the oculomotor nerve. It can also occur as a consequence of severe birth trauma.

Isolated idiopathic, hereditary (autosomal recessive), neurological defect (involves other signs and symptoms)

Question 10

What are the common aetiologies of acquired CNIII palsies?

Answer 10

• Vascular disorders such as diabetes, heart disease, atherosclerosis and aneurysm, particularly of the posterior communicating artery
• Space occupying lesions or tumours, both malignant and non-malignant
• Inflammation and infection
• Trauma
• Demyelinating disease (multiple sclerosis)
• Autoimmune disorders such as myasthenia gravis
• Post-operatively as a complication of neurosurgery
• Cavernous sinus thrombosis

Question 11

What motor actions does the CNIII do?

Answer 11

Motor –
Innervates the majority of the extraocular muscles (levator palpebrae superioris, superior rectus, inferior rectus, medial rectus and inferior oblique).

Question 12

What parasympathetic/autonomic actions does CNIII do?

Answer 12

Parasympathetic/Autonomic – Supplies the sphincter pupillae and the ciliary muscles of the eye.

Question 13

What sympathetic actions does CNIII do?

Answer 13

No direct function, but sympathetic fibres run with the oculomotor nerve to innervate the superior tarsal muscle (helps to raise the eyelid).

Question 14

What are symptoms of CNIII palsy?

Answer 14

• Ptosis (drooping upper eyelid) – unopposed activity of the orbicularis oculi muscle as result of LPS paralysis
• ‘Down & Out’ eye position – paralysis of superior, inferior and medial rectus and the inferior oblique = unopposed activity of the lateral rectus and superior oblique
• Mydriasis – unopposed action of the dilator pupillae muscle

If due to a compression by a PCA (posterior communicating artery aneurysm) it’ll be painful and mydriasis will be present. Trauma also involves the pupil.

Vascular acquired 3rd nerve palsy usually results in a full recovery

Question 15

Which type of nerve palsy usually results in a full recovery?

Answer 15

Vascular acquired CNIII palsy

Question 16

What AHP is expected in CNIII palsy? What symptoms will they experience with an AHP?

Answer 16

• Head turn in the opposite direction to the affected eye
• Notice AHP: in those with a single muscle affected/palsy, as only one is affected they should have a larger area of BSV.
  Those with a complete 3rd nerve palsy will have a small area of BSV due to a large area of incomitancy as a result of the affected EOMs and restricted ocular motility = likely to have an AHP
• No AHP: anyone with complete 3rd nerve palsy, pupil involvement and ptosis.
  Because of the droopiness of the eyelid, it will obscure the diplopia and the px will see single

Question 17

If there is no AHP in CNIII what does this mean?

Answer 17

• No AHP: anyone with complete 3rd nerve palsy, pupil involvement and ptosis.
  Because of the droopiness of the eyelid, it will obscure the diplopia and the px will see single so don’t need an AHP

Question 18

What will CT show of CNIII palsies?

Answer 18

• Incomitant exotropia (greater on head turn to the same side)
• Hypotropia
• Intorsion
• Can be broken down between complete and incomplete 3rd nerve palsy

Question 19

How does a COMPLETE CNIII palsy look?

Answer 19

Ptosis and deviation will be out and down. Eye cannot move in, up or down. The pupil will be large and will not react to light.

Question 20

What will ones OMs look like in a COMPLETE CNIII palsy vs. an INCOMPLETE CNIII palsy?

Answer 20

Full – abduction

Limited – Elevation, depression, adduction

Question 21

How can COMPLETE CNIII palsy be classified?

Answer 21

1. Both the superior and inferior divisions are involved
2. Pupil may or may not be involved
3. Total or partial (depending on severity of motility)

Question 22

What happens in complete CNIII when there’s a complete ptosis?

Answer 22

Outcome of complete ptosis in a congenital 3rd nerve palsy leads to stimulus deprivation amblyopia and suppression. It prevents diplopia but, as recovery occurs the lid improves and diplopia will be appreciated again.

When it is partial ptosis they may have some binocular potential with AHP and will result in strabismic amblyopia if the eyelid obstructs the pupil.

Question 23

What should we assume an acquired CNIII palsy is caused by until proven otherwise?

Answer 23

An acquired complete 3rd nerve palsy is presumed to be a result of posterior communicating artery aneurysm in absence of trauma until proven otherwise.

Question 24

What is Incomplete/Partial CNIII palsy divided into?

Answer 24

2 Divisional Palsies
- Superior Division (SR, LPS)
- Inferior Division (MR, IO, IR and inferior branch to ciliary ganglion controlling sphincter and ciliary muscle)

& Single Muscle Palsy (IR, SR, MR)

Question 25

What is Superior Division palsy?

Answer 25

A divisional partial/incomplete CNIII palsy of SR or LPS.
Usually a result of superior orbital fissure aetiology through trauma or tumours

Question 26

What is Inferior Division palsy?

Answer 26

A divisional partial/incomplete CNIII palsy of MR, IO, IR and inferior branch to ciliary ganglion controlling sphincter and ciliary muscle

Question 27

What is Single Muscle palsy?

Answer 27

An incomplete CNIII palsy of the IR, SR or MR
= will be diagnosed as Duanes Retraction Syndrome, Thyroid Eye Disease or Browns Syndrome

Question 28

What does a single muscle palsy of the IR need to be differentiated with?

Answer 28

A singular incomplete muscle palsy of the IR needs to be differentiated with Myasthenia Gravis (IR very rare, must exclude mechanical restrictions like thyroid eye disease)

Question 29

Are complete or incomplete CNIII palsies the most common?

Answer 29

Incomplete
Partial 3rd nerve palsies are more common than complete palsies and can present with variable duction limitations of the affected extraocular muscles and varying degrees of eyelid ptosis and/or pupillary dysfunction.

Question 30

What aetiologies for CNIII palsies can lead to pupil sparing?

Answer 30

Pupil sparing can occur in ischaemia as well as inflammatory and aneurysm. It is spared in diabetes and hypertension as it’s an occlusive disease of network of small blood vessels supplying the nerve (compressed or compromised). Pupillomotor fibres travel in outer layers of nerve therefore closer to nutrient blood supply enveloping the nerve therefore pupil responses are normal.

Question 31

What are the symptoms of complete CNIII palsy?

Answer 31

Complete 3rd nerve palsies will present with a complete eyelid ptosis with the eye in a downward and outward position and the inability to adduct, infraduct, or supraduct. Patients will also have a dilated pupil with sluggish reaction to light.

Question 32

What is Aberrant Regeneration?

Answer 32

Aberrant regeneration of the third cranial nerve, or oculomotor synkinesis, refers to the abnormal response to firing of the oculomotor nerve causing paradoxical co-contraction of muscles. Following an acute onset CNP a certain amount “miswiring” can occur as the damaged nerve regenerates, resulting in bizarre eye movements which do not improve with time or can be corrected with surgery.

The axons retract when damaged and grow forward again they enter wrong myelin tube to supply inappropriate muscles
IR to LPS

Question 33

What is aberrant regeneration common in?

Answer 33

CNIII palsy when caused by aneurysms, trauma, tumour (rare) and congenital (uncommon).

Question 34

In what cases of CNIII palsy is aberrant regeneration not going to occur?

Answer 34

It will not occur in diabetic or hypertensive cases which is presumed to be due to the structural framework of the nerve remaining intact.

Question 35

When is aberrant regeneration likely to occur?

Answer 35

This occurs around 5 weeks after the 3rd nerve palsy in children and 2-3 months after acute onset in adults.

Question 36

What are examples of aberrant regeneration?

Answer 36

• Eyelid retraction / pupil constriction on adduction, upgaze and downgaze
• Paradoxical eye movements (i.e. adduction on attempted up / downgaze)

Question 37

What are 4 features of aberrant regeneration?

Answer 37

• Elevation of the upper eyelid on down-gaze or adduction (Pseudo Von-Graefe phenomenon)
• Adduction of the eye on attempted up-gaze (the eye does not move entirely up, but adducts as well)
• Pupil constriction on attempted adduction +/- down-gaze
• Retraction of globe on attempted elevation / depression
  Co-contraction of SR / IR

Question 38

How do we check that CNIV palsy is not at play in a CNIII palsy?

Answer 38

Need to check that the 4th nerve is intact:
- Main action SO depression on ADDuction

• Make patient abduct the eye and then try to look down as much as they can (even though px with 3rd nerve palsy won’t be able to depress a lot). Examiner should look for intorsion (iris landmark or conjunctival vessel) to confirm fourth nerve is intact

This is done because:
- Depression and adduction affected in 3rd nerve need to establish if 4th nerve functioning

• Establish aetiology and therefore what scan to perform

Question 39

What are the ocular movement findings in CNIII?

Answer 39

• Lift the ptotic lid except when looking for aberrant regeneration
• Limitation of movement in all directions of gaze bar laterally and down in adduction
• Limited adduction, elevation and depression. Unlikely to find a position of BSV due to degree of incomitance on ocular motility because the field of BSV will be extremely small (that’s why prisms aren’t beneficial for these patients)

Question 40

What is the field of BSV like in CNIII palsy?

Answer 40

Very small!
Unlikely to find a position of BSV due to degree of incomitance on ocular motility because the field of BSV will be extremely small (that’s why prisms aren’t beneficial for these patients) usually to the LR (abduction).

Question 41

Look at the Hess Charts!