Cranial Nerves Flashcards
Facial Nerve - Supply
Supply - ‘face, ear, taste, tear’
face: muscles of facial expression
ear: nerve to stapedius
taste: supplies anterior two-thirds of tongue
tear: parasympathetic fibres to lacrimal glands, also salivary glands
Causes of Bilateral vs Unilateral Facial Nerve Palsy
Causes of bilateral facial nerve palsy sarcoidosis Guillain-Barre syndrome polio, Lyme disease botulism
Causes of unilateral facial nerve palsy - as above plus
Lower motor neuron Bell's palsy Ramsay-Hunt syndrome (due to herpes zoster) acoustic neuroma parotid tumours HIV multiple sclerosis* diabetes mellitus
Upper motor neuron
stroke
*may also cause an UMN palsy
Facial Nerve Lesions - UMN vs LMN
LMN vs. UMN
upper motor neuron lesion ‘spares’ upper face i.e. forehead
lower motor neuron lesion affects all facial muscles
Bilateral Facial Nerve Palsy - Diagnosis: Example Question
A 27-year-old man attends ambulatory care with a one day history of facial droop. He is a mountain bike instructor and is extremely anxious that this may be related to a fall last month. He hasn’t been riding for the last month because he has felt unwell with aches and pains and some odd bruising up his leg.
On examination he has a bilateral VII nerve weakness but no other cranial nerve lesions detected. The arms and legs show no focal neurology.
Skin is intact with no skin lesions seen. There is no evidence of any joint effusions and all joints appear to have a full range of motion
Investigations:
Haemoglobin 127 g/L (130-180)
White cell count 10.0 × 109/L (4.0-11.0)
Chest X-ray Normal
What is the most likely diagnosis?
Sarcoidosis > Lymes Disease Syphilis Bells Palsy Subdural Haemorhhage
This patient has bilateral seventh nerve palsy. The most likely diagnosis is Lymes Disease. Lymes disease is caused by Borelli bacteria that affects human from ticks that also feed from rodents.
Infected tick bites are common especially in the New Forest area of the UK. 70-80% of persons infected develop a rash (erythema migrans - target rash). Weeks after the initial bite the spirochetes spread via the bloodstream to joints, heart and nervous system.
Syphilis is on the rise but the more likely cause of the bilateral seventh nerve palsy is lymes disease especially given the rash.
Subdural haemorrhage can occur after trauma - such as bike fall. Symptoms are likely to occur within days rather than having a first presentation one month after the accident.
Third Nerve Palsy - Features!
Third nerve palsy
Features
eye is deviated ‘down and out’
ptosis
pupil may be dilated (sometimes called a ‘surgical’ third nerve palsy)
Third Nerve Palsy - Causes
Causes
diabetes mellitus
vasculitis e.g. temporal arteritis, SLE
false localizing sign* due to uncal herniation through tentorium if raised ICP
posterior communicating artery aneurysm (pupil dilated)
cavernous sinus thrombosis
Weber’s syndrome: ipsilateral third nerve palsy with contralateral hemiplegia -caused by midbrain strokes
other possible causes: amyloid, multiple sclerosis
*this term is usually associated with sixth nerve palsies but it may be used for a variety of neurological presentations
Third Nerve Palsy: Causes - Example Question
A 69 year old male presenting with a 4 month history of progressive ‘droopiness’ of his left eyelid. He reports that in the last 2 weeks, he has been unable to lift his eyelid at all, which he says is fortunate considering he gets double vision now when he lifts his eyelid with his fingers. He underwent a renal transplant in 1988, which continues to function well, and previously had a squamous cell and malignant melanoma resected 2 and 5 years ago respectively.
On examination, you note complete ptosis, loss of vertical eye movements and loss of adduction in his left eye. On head tilt to the right, he is unable to depress left eye. His right eye demonstrates full eye movements. The left pupil is unreactive and larger in diameter compared to the right. There is also loss of sensation at left nasal skin fold and left forehead with sparing of his left chin. He has no facial weakness, hearing loss or palatal asymmetry. He denies headache or retroorbital pain.
Where is the likely lesion?
Left ocular neuromuscular junction > Left cavernous sinus Left superior orbital fissure Cerebral aqueduct Left midbrain
The patient has deficits of his oculomotor nerve with parasympathetic involvement, involvement of trochlear nerve and also the first and second branch of the trigeminal nerve, hence sparing of his left chin as supplied by the mandibular branch of the trigeminal nerve. Loss of pupilary reflexes in the left eye is a result of third nerve involvement and not necessarily retinal or optic nerve pathology. Ability to abduct the left eye suggests the abducens nerve is intact. The only anatomical location involving all these structures is the left cavernous sinus. (What is inside the Cavernous Sinus? - Learn)
The possible cause for this cavernous sinus syndrome is interesting: the insidious gradual course goes against an acute cavernous sinus thrombus. A significant, expanding internal carotid aneurysm, which runs inside the cavernous sinus with the parasympathetic nerves wrapped around it, is a possibility. However, the key is the recognition that the patient is chronically immunosuppressed due to his renal transplant, increasing his risk of opportunistic infections such as fungi and also dermatological malignancies.
PAINFUL Third Nerve Palsy = Neurosurgical Emergency
Presentation with a painful third nerve palsy is a neurosurgical emergency that normally presents to the medics as it may indicate an expanding posterior communicating artery aneurysm. Urgent CT angiogram of the cerebral vessels is required for diagnosis. Management is with surgical clipping. If this does not happen quickly, there is a risk of death from rupture or there may be permanent ptosis and eye movement deficit.
It is important to be able to differentiate between surgical causes of third nerve palsy (eg the above, or a tumour), and medical causes, eg diabetes or vasculitis. The surgical causes indicate an emergency whilst the medical causes are likely chronic conditions requiring optimisation of medical management. The parasympathetic fibres of this nerve are on the periphery of the nerve and the sympathetic fibres are in its centre. Therefore, a fixed dilated or sluggish pupil indicates that the parasympathetic fibres have been wiped out (eg by external compression from an aneurysm or tumour), leaving unopposed sympathetic tract flow within this nerve (dilating the pupil). The blood supply to the nerve is within its internal portion, meaning medical causes like diabetes or vasculitis wipe out the sympathetic portion of the nerve, leaving unopposed parasympathetic flow and consequently a constricted pupil.
The trochlear nerve sits right next to the oculomotor nerve, meaning if a structural cause is big enough, it will take the trochlear nerve out too. The trochlear nerve is responsible for intorsion of the eye (ie internal rotation in the plane of the face). So when you test for a 3rd nerve palsy, you should also test for a 4th nerve palsy by asking the patient to follow your finger as you draw a half-circle from out to in (anti-clockwise): ie your 9’oclock to 3 o’clock. If the eye fails to follow, this is a failure of intorsion.
Example Question:
A 75-year-old woman presents with a 24-hour history of gradual onset, severe 10/10, frontal headache associated with double vision. The history is otherwise unremarkable. On examination, she has a partial ptosis of the right eye and a pupil resting outwards and downwards with a dilated sluggishly reacting pupil. There is a failure of intorsion of the right eye. Neurological and physical examination are otherwise unremarkable. She has normal routine blood tests and a normal plain CT head. What is the most important next investigation?
Lumbar puncture > CT angiogram cerebral vessels. Carotid artery biopsy Indomethacin trial Single fibre EMG of the ocular muscles
Painful Third Nerve Palsy?
Think Posterior Communicating Artery Aneurysm!
Facial Nerve and Palsies
Supply = 'Face, Ear, Taste, Tear' FACE = Muscles of facial expression EAR = Nerve to Stapedius TASTE = Supplies anterior 2/3 of the tongue TEAR = Parasympathetic fibres to lacrimal glands, also salivary glands
Causes of bilateral facial palsy
- Sarcoidosis
- Guillain-Barre
- Polio
- Lyme disease
Causes of Unilateral Facial Palsy AS FOR BILATERAL PLUS - Bell's Palsy (LMN) - Ramsay-Hunt syndrome (LMN) - Acoustic neuroma (LMN) - Parotid tumour (LMN) - HIV (LMN) - MS (UMN + LMN) - DM (LMN) - Stroke (UMN)
UMN LESIONS SPARE FOREHEAD
LMN AFFECTS ALL FACIAL MUSCLES
Therefore Differential of Unilateral UMN Facial Nerve Palsy can only be either Stroke or MS!
Trochlear Nerve Lesion
NYSTAGMUS on looking DOWN and OUT
Bell’s Palsy
Acute, unilateral, idiopathic, facial nerve paralysis
Peak incidence = 20-40s
More common in pregnant women
Features:
- LMN facial nerve palsy - FOREHEAD AFFECTED
- Patients may also notice post-auricular pain, seen in 50%
- Altered taste
- Dry eyes
- Hyperacusis
Mx:
Prednisolone 1mg/kg for 10d within 72 of onset
Prescription of artificial tears and eye lubricant for eye care
Prognosis:
- if left untreated, around 15% of patients have permanent moderate to severe weakness
Acoustic Neuroma
NB Loss of Corneal reflex, think Acoustic Neuroma
Also called Vestibular Schwannomas
Account for 5% Intracranial tumours, 90% of Cerebellopontine angle lesions
Features = predicted by affected CNs (5,7,8)
CN VIII: Hearing loss, Vertigo, Tinnitus
CN V: Absent corneal reflex
CN VII: Facial Palsy
NB: Bilateral acoustic neuromas are seen in NF2
Ix of Choice = MRI of Cerebellopontine angle
Bitemporal Hemianopia
= Lesion of optic chasm
Upper Quadrants affected = Inferior chiasmal compression
> Pituitary Tumour
Lower Quadrants affected = Superior chiasmal compression
> Craniopharyngioma
Visual Field Defect - Example Question
A 59 year old male presents with 4 day history of sudden onset visual disturbance in his right eye. He reports it to be his first episode with no previous history of visual problems. His past medical history includes type 2 diabetes mellitus, hypertension and raised BMI. He is an active smoker of 40 pack years.
On examination, a right relative afferent papillary defect is detected. Pupils were equal in size. A visual field defect is demonstrated in the inferior nasal field of the right eye without a precise quadraniopic or altitudinal pattern. Temporal arteries are non-tender and not thickened. Visual acuity on Snellen chart in left eye was 6/6, 6/18 in right. Colour vision on Ishihara plates were 17/17 on left, 5/17 on right. Fundoscopy is unremarkable. Examination of the upper and lower limbs are unremarkable, no language deficits are noted. Auscultation revealed normal heart sounds and no bruits.
His blood tests are as follows:
Hb 15.4 g/dl
Platelets 190 * 109/l
WBC 7.8 * 109/l
ESR 5 mm/hr
Na+ 141 mmol/l
K+ 3.9 mmol/l
Urea 5.6 mmol/l
Creatinine 80 µmol/l
What is the most likely diagnosis?
Right retinal infarct Right temporal arteritis > Right non-arteritic ischaemic optic neuropathy Left middle cerebral artery ischaemic stroke Left occipital ischaemic stroke
Visual field defects are common presentation in clinical practice and MRCP part 2. The first feature to notice here is the monocular presentation, which indicates the lesion must be anterior to the optic chiasm. Next, fundoscopy is unremarkable, which would be unusual for a retinal infarct, most likely secondary to central or branch retinal artery occlusion.
Typically, an acute retinal infarct should reveal a classic cherry red spot, pale fundus and possible visualisation of the embolus. On locating the lesion to be at the optic nerve, the cause must be established: typically is this optic neuritis, arteritic or non-arteritic anterior ischaemic optic neuropathy. Optic neuropathy typically produces a correlated deficit in visual acuity with colour vision, allowing differentiation from optic neuritis, where colour vision is frequently better preserved.
Lastly, this patient has a normal ESR, is under 60 and has no local or systemic features of vasculitis, particularly temporal arteritis. In addition, he has multiple vascular risk factors, making a non-arteritic ischaemic anterior optic neuropathy most likely. Management involves optimisation of vascular risk factors and there is limited evidence for a tapering dose of oral prednisolone. Most patients can expect to improve by 3 lines of a Snellen chart by 6 months.
