Lecture 13 6th nerve palsy Flashcards
What is the 6th nerve called?
Where is its nucleus found?
What muscles does it innervate?
What pathway does the nerve take?
Why is is susceptible to lesions?
*Abducens nerve
*6th nerve nucleus is located at the base of the 4th ventricle in the pons portion of the brainstem
*Contains 2 types of cells:
-motor neurones: innervate the lateral rectus
-inter-nuclear neurones: innervate the contralateral medial rectus via the MLF
*Nerve does not cross so Right 6th nerve nucleus innervates right lateral rectus etc.
-6th nerve leaves brainstem anteriorly and travels forward where is ascends the clivus.
-it passes over the apex of the Petrous temporal bone
-it enters the cavernous sinus and then enters the bony orbit via the superior orbital fissure.
-it terminates at the lateral rectus muscle.
6th nerve has a long course
Where can you get lesions affecting the 6th nerve?
When 6th nerve passes through cavernous sinus, lesions can occur.
Close proximity to major vessels and other nerves, you can get multiple nerve palsies.
What is the primary action of the LR
what is its contralateral synergist?
abduction
medial rectus
How can you classify a 6th nerve palsy?
acquired-nuclear
-infranuclear
congenital
What is the aetiology of a acquired 6th nerve palsy in adults?
*Microvascular (most common) DM, HTN, HBP
*Vascular changes
*Neoplasm
*Trauma- carotid cavernous fistula
*Neurological disorder- migraine, MS, raised ICP
*Iatrogenic
*Idiopathic
*Inflammatory
What is the aetiology of congenital 6th nerve palsy?
What is the aetiology of acquired 6th nerve palsy in children ?
-traumatic birth
-not associated with other abnormalties
-often resolves
*Intracranial tumours (most common) pons gliomas, brainstem gliomas
*Raised intracranial hypertension
*Idiopathic (resolve in 8 to 12 weeks)
*Trauma
*Inflammation
*Post viral
*Secondary to middle ear disease, cerebral venous sinus thrombosis or drugs (tetracycline, steroids)
What are the clinical features of a unilateral 6th nerve palsy?
*Esotropia greater in the distance (px may be binocular for near with esophoria)
*Limitation of abduction on the affected side
*Adoption of AHP-face turn to the affected side to achieve binocularity.
*Field of BSV displaced to the unaffected side
What orthoptic tests should you do to investigate 6th nerve palsy?
CT distance and near with and without specs, with and without AHP
OM ductions and versions
Lateral gaze incomitance
Hess chart
Field of BSV
What is the muscle sequelae for LR under action?
- LR under action of affected eye
- MR over action of unaffected eye
- MR over action of affected eye
- LR under action of unaffected eye
What are the features of bilateral 6th nerve palsy?
*Affects both LR
*Results in bilateral abduction deficit
*Can be symmetrical or asymmetric.
*May adopt AHP to fix with one eye or the other to gain BSV
What is the management in children?
*RARE in children
*Must establish cause: MRI and referral to a neurologist
*May have spontaneous recovery (seen in viral and idiopathic cases)
*Important that BSV is not lost and we want to prevent amblyopia
*Encourage adoption of AHP
*Fresnel prisms if indicated
*BTXA to MR (botulinum toxin)
*Occlusion therapy for amblyopia
What is the management in adults?
*New onset palsies are to be followed up regularly to monitor spontaneous recovery
*Most microvascular nerve palsies fully resolve within 12 months
*Some do not fully recover.
*Natural progression of microvascular palsies get worse before they improve
What is the differential diagnosis of 6th nerve palsy?
*Duane’s retraction syndrome
*High myopia
*Graves Orbitopathy (TED)
*Orbital Trauma
*Decompensating distance esophoria
*Age related distance esotropia
*Spasm of the near reflex
*Myasthenia Gravis
What are options for conservative management?
Occlusion
-Indicated in patients with recent onset and large angle esotropia.
-Patch or Bangerter foil
- Fresnel prisms
Used in patients with smaller deviations (may require changing)
-Use of plano glasses
Prism incorporation after a period of stability (often 6 months)
What surgical management can you do for a unilateral 6th nerve palsy?
Small deviations and reasonable abduction
* MR recession and LR resection of affected eye
Complete absence of abduction
* BTXA to ipsilateral MR to assess abduction (Limitation may be partially due to contracture of MR)
No Lateral rectus function
*Transposition procedure (many different techniques)
*SR and IR transposed and sutured to LR
*BTXA may be given to MR of affected eye at time of surgery
