CN 4 palsy

Question 1

what are the causes of isolated CN 4 palsy?

Answer 1

• Idiopathic (common)
• Trauma (frequently cause bilateral)
• Microvascular lesions (relatively common)
• Aneurysms, tumours (extremely rare)

Question 2

where is CN4 nucleus located

Answer 2

Nucleus is located at level of inferior collicul

Question 3

what is the main function of superior oblique?

Answer 3

intorsion, and depression in adducted position

Question 4

what are the signs of left CN4 palsy?

Answer 4

Peripheral lesions cause ipsilateral CN4 palsy, nuclear lesions cause contralateral palsy

• Left hypertropia in the primary position, increasing on right gaze
• Limitation of left depression, most marked in adduction
• Left extorsion, greatest in abduction

Weak intorsion 🡪 contralateral head tilt (to right)
Weak depression 🡪 chin slightly depressed

Question 5

What is the management of CN4 palsy

Answer 5

Congenital decompensated and presumed microvascular palsies commonly resolve spontaneously –> Assess for ischaemic risk factors; if due to ischaemia, CN4 palsy typically resolves in 3 months

For diplopia

• Monitor with Hess chart & binocular single vision test
• Occlusion
• Fresnel prism
• Surgical correction

Strabismus surgery, is not infrequently required in:

• Trauma: to correct troublesome diplopia
• Childhood cases: to correct substantial compensatory head posture