Cranial Nerve Palsy - III : Oculomotor Nerve

Question 1

Anatomical Course of Oculomotor Nerve.

Answer 1

1. Anterior Aspect of Midbrain.
2. Inferior to PCA and Superior to SCA.
3. Pierces Dura Mater and Enters Lateral Cavernous Sinus.
4. Travel with Sympathetic Branches from Internal Carotid Plexus in Sheath.
5. Leave Cranial Cavity via Superior Orbital Fissure.

Question 2

Motor Functions of Superior Branch of Oculomotor Nerve.

Answer 2

SL (Sri Lanka = Superior) :
1. Superior Rectus (elevate eyeball).
2. Levator Palpabrae Superioris (raise upper eyelid).
2* is elevated with Superior Tarsal Muscle innervated by Sympathetic fibres that travel with the Nerve.

Question 3

Motor Functions of Inferior Branch of Oculomotor Nerve (3).

Answer 3

IMI :

1. Inferior Rectus (depress eyeball).
2. Medial Rectus (adduct eyeball).
3. Inferior Oblique (elevate, abduct and laterally rotate eyeball).

Question 4

Parasympathetic Functions of Oculomotor Nerve.

Answer 4

1. Sphincter Pupillae (Constriction).

2. Ciliary Muscles (Contract to Cause Lens to Become Spherical : Short Range Vision).

Question 5

Ciliary Ganglion and Oculomotor Nerve (3).

Answer 5

1. Pre-Ganglionic Parasympathetic Fibres travel with Inferior Branch of Oculomotor Nerve.
2. Branch off and synapse in the Ciliary Ganglion.
3. Post-Ganglionic Fibres carried to eye by Short Ciliary Nerves.

Question 6

Origin of Oculomotor Nerve.

Answer 6

Midbrain-Pontine Junction in Brainstem.

Question 7

Commonest Structural Causes of Oculomotor Nerve Palsy (3).

Answer 7

1. Raised ICP - Compression against Temporal Bone.
2. Posterior Communicating Artery Aneurysm (with associated pain) - commonest.
3. Cavernous Sinus Infection/Trauma.
4. Weber’s Syndrome.

Question 8

Pathological Causes of Oculomotor Nerve Palsy (4).

Answer 8

1. Diabetes.
2. MS.
3. Myasthenia Gravis.
4. GCA.

Question 9

Clinical Features of Oculomotor Nerve Palsy (3).

Answer 9

1. Ptosis (paralysis of Levator Palpabrae Superioris).
2. Down and Out at Rest (Paralysis of Superior, Inferior and Medial Rectus and Inferior Oblique).
3. Dilated Pupil (Unopposed Action of Dilator Pupillae).
4. DOUBLE VISION.

Question 10

Which Clinical Feature is also known as Surgical Third Nerve Palsy?

Answer 10

Dilated Pupil (Mydriasis) = the parasympathetic fibres run external to the nerve.

Question 11

What is a False Localising Sign?

Answer 11

Uncal. Herniation through Tentorium if Raised ICP.

Question 12

What is Weber’s Syndrome?

Answer 12

Ipsilateral Cranial Nerve III Palsy with Contralateral Hemiplegia - caused by Midbrain Strokes.

Question 13

Differential Diagnoses of Mydriasis (Large Pupil). (6).

Answer 13

1. Third Nerve Palsy.
2. Holmes-Adie Pupil.
3. Traumatic Iridoplegia.
4. Phaeochromocytoma.
5. Congenital.
6. Drugs e.g. Anticholinergics, TCAs, Amphetamine, Cocaine.