6th NP Flashcards
what is the pathway of the 6th nerve LEARN
Abducens nucleus in the pons
Exits the brainstem at the junction between the pons and medulla
Enters the subarachnoid space and runs along dorello’s canal
Passes above the tip of the petrous temporal bone
Enters the cavernous sinus where it runs along side the internal carotid artery
Enters the lateral aspect of the superior orbital fissure and passes anteriorly to innervate the lateral rectus
aetiology of 6th NERVE PALSY in over 50s
Most Common Aetiology in over 50’s is a Microvascular Incident due to:
* Diabetes
* Hypertension
* High Cholesterol
Other aetiologies include:
* Trauma
* Giant cell arthritis- emergency !!
* Stroke
Aetiology of 6th NP - UNDER 50s
Multiple Sclerosis - causes 6th NP to come and go due to demyelination and regeneration
Raised Intracranial pressure due to space-occupying lesions
Increased Idiopathic intracranial Hypertension (IIH) - benign condition, raised ICP with no tumour, due to obesity usually, VF loss due to papilledema
Trauma
Cavernous sinus mass - Fistula due to rush of blood
Viral infection
Aetiology of 6th NP - UNDER 16s
Congenital VI Palsy - can be lesion at nucleus that hasn’t developed
Space-occupying lesions -
tumour *** - main cause
Trauma
Idiopathic
Viral Infection affecting ears,
nose or throat
Hydrocephalus
Clinical Features of 6th NP
Esotropia in primary position greater on distance fixation - wont have diplopia at near
Esotropia increasing in size on attempted abduction of affected eye
Limited abduction of affected eye
Patient complaining of uncrossed diplopia (more so on distance fixation)
Patient may have face turn to affected side
Field of BSV moved towards unaffected eye
Differential diagnosis of 6th NP
Myasthenia Gravis - can mimic anything, weakness of a muscle
Duane’s Retraction Syndrome – Type 1, congenital cant abduct
Infantile Esotropia
Mobeius Syndrome – combined 6th and 7th nerve palsy - congenital
Medial Wall Fracture
investigations of 6th NP
Start with VA - difference in each eye
Assess Far Distance (cover test and measurements)
Lateral Version measurements to compare varying sizes of esotropia
Smooth Pursuits will show limitation of abduction of the affected eye
Saccades may show hypometria of the affected eye
Lee’s screen will support the smooth pursuit findings and allow comparison of palsy at future visits
Unless patient has high risks factors indicating microvascular incident then patient most likely requires neuro-imaging to determine cause of palsy
Important to establish aetiology of palsy to rule out anything sinister such as space occupying lesion or multiple sclerosis
Case History of 6th NP
Presenting usually with Horizontal Diplopia that is worse in the distance
· May be aware of using a face-turn to achieve single vision (BSV)
· Questions on headaches/vascular causes/visual changes
When did this begin?
Management of 6th
Orthoptic
Prisms to join diplopia and restore binocular single vision
If deviation too large to control with prisms then occluding one eye will alleviate patients symptoms of diplopia
Allow 6 month for recovery
If only partial recovery then Botox or surgery can be used to regain BSV in primary position
types of 6th syndromes
Moebius syndrome
* Congenital
* Bilateral 6th and 7th Nerve palsy
* No known genetic cause
* Insufficient eyelid closure
* Volitional Eye Lid Closure
* Amblyopia
* DVD
Gradenigo’s Syndrome
Involvement of VI N in combination with:
VII ( facial palsy)
V ( facial or eye pain)
VIII ( loss of hearing)
Cause: inflammation of the petrous bone secondary to middle-ear infections
Most likely in children
