Year 3 Strab > Lesions & Brainstem Function > Flashcards

Lesions & Brainstem Function Flashcards

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1
Q

What cranial nerves are above the pons?

A

CNI - CNIV

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2
Q

What cranial nerves are in the pons?

A

CNV - CNVIII

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3
Q

What cranial nerves are in the medulla?

A

CNIX - CNXII

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4
Q

What is your mnemonic for the cranial nerves?

A

Only One Of The Two Athletes Felt Very Good, Victorious and Happy

Olfactory nerve (CN I)
Optic nerve (CN II)
Oculomotor nerve (CN III)
Trochlear nerve (CN IV)
Trigeminal nerve (CN V)
Abducens nerve (CN VI)
Facial nerve (CN VII)
Vestibulocochlear nerve (CN VIII)
Glossopharyngeal nerve (CN IX)
Vagus nerve (CN X)
Accessory nerve (CN XI)
Hypoglossal nerve (CN XII)

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5
Q

What is the pyramidal tract also known as?

A

The corticospinal tract

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6
Q

What is the Pyramidal Tract?

A

Also known as the corticospinal tract, is a central pathway for voluntary movement in the brain, originating from the cerebral cortex and carrying motor signals to the brainstem and spinal cord.

Fibres originate in the cerebral cortex and carry upper motor neurons to the spinal cord (corticospinal) and to the brainstem (corticobulbar). This then goes to the lower motor neurons (synapse at the spinal cord) and to the muscle.

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7
Q

What are the cerebral peduncles?

A

The cerebral peduncles are two stalks that attach the cerebrum to the brainstem located in the anterior midbrain.

Cerebral peduncles have both ascending and descending nerve fibres between brain and brainstem

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8
Q

Where is the Red Nucleus?

A

In the midbrain

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9
Q

What does the Red Nucleus do?

A

Receives input from contralateral cerebellum and ipsilateral motor cortex

It’s involved in motor control, coordinating limb movements and maintaining muscle tone

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10
Q

What are the 3 categories of brainstem lesions?

A
  1. Nuclear
  2. Internuclear (between nuclei such as CNIII and CNVI is the MLF that co-ordinated horizontal eye movement)
  3. Infranuclear (below the level of the nuclei)

Associated with other neurological signs because of other structures in close proximity

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11
Q

What is the MLF?

A

Medial Longitudinal Fasciculus

Paired white matter tract in the brainstem that coordinates eye movements and is essential for smooth pursuit and vestibular-ocular reflexes

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12
Q

What is the action of the IO and its innervation?

A

Action: Elevate eye when eye is adducted and extortion when the eye is abducted

Innervation: Oculomotor, uncrossed

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13
Q

What is the action of the MR and its innervation?

A

Action: Adduction

Innervation: Oculomotor, uncrossed

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14
Q

What is the action of the IR and its innervation?

A

Action: Depresses eye when abducted

Innervation: Oculomotor, uncrossed

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15
Q

What is the action of the SR and its innervation?

A

Action: Elevate the eye when abducted

Innervation: Oculomotor, crossed

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16
Q

What is the action of the LPS and its innervation?

A

Action: Raise eyelids

Innervation: Oculomotor, both crossed & uncrossed

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17
Q

What is the action of the SO and its innervation?

A

Action: Depress eye when the eye is adducted and intort eye when the eye is abducted

Innervation: Trochlear, crossed

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18
Q

What is the action of the LR and its innervation?

A

Action: Abduct eye

Innervation: Abducens, uncrossed

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19
Q

How many nuclei does CNIII have & what are they?

A

Two nuclei

Oculomotor nerve nucleus - SR, IR, MR, IO and levator palpebrae superioris

Edinger-Wesphal nucleus (accessory) - sphincter pupillae and ciliary body (parasympathetic)

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20
Q

How many afferent nerve fibres does CNIII have and what do they do?

A

Two types of efferent nerve fibres
Somatic (EOMs) and visceral (sphincter and ciliary body)

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21
Q

Where does CNIII originate?

A

At the midbrain at the level of the superior colliculus

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22
Q

What do the CNIII sub-nuclei do?

A

All sub-nuclei innervate ipsilateral muscles, except for two:
- SR sub-nucleus
- Central caudal nucleus (CCN)

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23
Q

What does the central caudal nucleus of CNIII do?

A

Controls the eyelids

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24
Q

What does the Edinger-Westphal nucleus do?

A

Involved in the parasympathetic pathway (sphincter muscle in near and light reflex)

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25
If someone has bilateral CNIII or bilateral ptosis likely indicate?
Likely nuclei or brainstem in origin
26
What happens if there's a nuclear lesion of CNIII?
Central caudal nucleus (CCN) supplies both levator muscles - Lesion results in bilateral ptosis - With / without unilateral SR limitation If bilateral limitation of elevation Lesion affecting SR subnucleus
27
What does fascicular mean?
Fascicular (still within the brainstem after exiting nucleus) then after this becomes a nerve (after exiting the brainstem)
28
What do fascicular lesions of CNIII lead to?
If unilateral limitation of elevation - Not SR subnucleus - Involvement of SR nerve fascicles (axons after leaving nucleus) Axons from 1 SR subnucleus cross and pass through contralateral, as well as ipsilateral, subnucleus
29
Where does the trochlear nerve (CNIV) originate?
Originates in the midbrain
30
Where does the CNIV exit?
It's the only one to leave via the posterior midbrain Thinnest (by number of axons) and longest intracranial nerve course
31
Which nerve are we unable to distinguish between nuclear and fascicular lesions with and why?
CNIV Unable to distinguish between nuclear and fascicular lesions due to complexity to the way it exits the brainstem and travels backwards
32
Does the trochlear cause contralateral or ipsilateral palsies?
Contralateral palsy to side of the nucleus
33
Why is CNIV prone to head injury?
Prone to head injury – shearing effect of moving the head forward and backwards and so vulnerable at the back of the brainstem
34
Where does CNVI originate?
Originates from the paramedian dorsal lower pons in the floor of the fourth ventricle lateral to the medial longitudinal fasciculus
35
Where does CNVI exit?
CNVI exits at the junction of the medulla and pons
36
What makes CNVI vulnerable?
Courses over the medial petrous apex towards the cavernous sinus making it vulnerable to brain tumours, IIH or to increases to IOP increases
37
Why is the CNVI known for 'false localising sign'?
You think that the CNVI is the cause of symptoms but there are 6 causes of a CNVI: 1. The brainstem syndrome 2. The elevated intracranial pressure syndrome 3. The petrous apex syndrome 4. The cavernous sinus syndrome 5. The orbital syndrome 6. The isolated 6th (microvascular) Azarmina and Azarmina (2013)
38
What do nuclear lesions of CNVI cause & Why??
Horizontal gaze palsy - problem could be in the brainstem Because ipsilateral LR and contralateral MR affected CNVI lies laterally to MLF so some neurons project to MLF and some neurons cross over contralaterally to innervate the contralateral MR sub-nucleus
39
What are some examples of brainstem syndromes?
Weber’s syndrome Benedikt’s syndrome Foville’s syndrome Millard-Gubler syndrome
40
What is Collier's sign?
Lid Retraction
41
What can cause Collier's Sign?
Unilateral or bilateral eyelid retraction due to midbrain lesions Characteristic feature of the dorsal midbrain syndrome (Parinaud syndrome) - Upward gaze palsy - Convergence-retraction nystagmus - Bilateral lid retraction (Collier’s sign) - Light-near dissociation
42
What is Weber's Syndrome?
Midbrain stroke syndrome A lesion affecting CNIII and cerebral peduncles in the midbrain leading to ipsilateral CNIII palsy and contralateral hemiparesis
43
What is Benedikt's Syndrome?
Paramedian midbrain syndrome Lesion affecting CNIII fascicles, red nucleus and cerebral peduncle in the midbrain Leads to ipsilateral CNIII palsy, contralateral hemiparesis, contralateral ataxia with hyperkinesis/tremor
44
What differentiates Benedikt's Syndrome and Weber's Syndrome?
Benedikt's has an associated tremor unlike Weber's (very similar)
45
What is Foville's Syndrome?
A lesion that affects CNVI, the ventral (anterior) pons and the pyramidal tract Leads to ipsilateral CNVI palsy, ipsilateral horizontal gaze palsy, ipsilateral facial palsy and contralateral hemiparesis
46
What is Millard-Gubler Syndrome?
A lesion at the base of the pons, antero-medially that affects the CNVI and CNVII fascicles and the pyramidal tracts Leads to ipsilateral CNVI palsy, ipsilateral facial nerve palsy (CNVII) and contralateral hemiplegia
47
What causes Divergence Paralysis?
Poorly understood, thought to be either that there's a divergence centre in brainstem around CNVI nucleus or a lesion of cerebellum or Arnold-Chiari malformation
48
What can cause Divergence Paralysis?
Raised ICP, MS, encephalitis, trauma, Miller-Fisher syndrome
49
What are the signs of Divergence Paralysis?
Signs: - Convergent deviation - Homonymous diplopia - Normal OM – full abduction either eye - Absent negative fusion amplitude
50
What do we need to differentiate divergence paralysis from?
- 6th nerve palsy - Concomitant ET - Convergence spasm
51
What is the treatment for divergence paralysis?
Treatment - May resolve – observation - Occlude/ Base out prisms - LR resections Large convergence deviation with homonymous diplopia. Not an OM issue (appears full) and difference from a convergence spasm. Rule out something sinister having happened and manage conservatively originally before considering surgery.
52
What are some examples of diseases that affect brainstem or OM function?
Parkinson’s disease Huntingdon’s disease Wernicke’s encephalopathy Whipple’s disease Arnold-Chiari malformation
53
What is Parkinson's Disease?
Degenerative condition of CNS due to insufficient production of dopamine - mainly affects substantia nigra in BS Causes: idiopathic (main), viral, inherited, trauma, drug induced Rigidity, tremor, slow movements (cognition, mood and sleep can also be affected) Medication can help in short term but effect reduces over time and no cure
54
What are the ocular features of Parkinson's Disease?
- Limited upgaze - Downgaze might be affected later - Hypometric saccades - Convergence insufficiency - Nystagmus - Reduced control of phoria – diplopia - Impaired smooth pursuit - Blepharospasm - Lid lag
55
What is Huntington's Disease?
Hereditary disorder of CNS Substantia nigra in BS may be involved or pre-nuclear (e.g. Frontal eye fields or superior colliculus) Loss of mobility, difficulty with speech and swallowing Ocular features - Difficulty initiating saccades (don’t track well) - Slow saccades - Impaired smooth pursuit
56
What is Wernicke-Korsakoff encephalopathy?
Spectrum of disorder caused by thiamine (B1) deficiency (B12) Common in alcoholics but can also occur in gastric disorders e.g. Crohn’s disease Gait ataxia, confusion, impaired short term memory Treat with thiamine injections but can progress to Korsakoff’s syndrome
57
What are the ocular features of Wernicke (acute, reversible) - Korsakoff (chronic, irreversible)?
Ocular features: - Weakness of abduction - Gaze-evoked nystagmus - INO - Vertical nystagmus - Horizontal/vertical gaze palsies - May progress to complete ophthalmoplegia
58
What is Whipple's Disease?
Caused by Tropheryma whippelii bacteria Systemic disorder: Weight loss, diarrhoea, gastro-intestinal bleeding, painful joints, arthritis, fever, fatigue, anaemia Treated with antibiotics, although bacteria can remain in CSF Can be fatal if left untreated Ocular features - Reduced vertical saccades - Vertical and horizontal gaze palsies - Pendular oscillations
59
What is Arnold-Chiari Malformation?
Anomaly in which cerebellar tonsils are displaced downwards towards foramen magnum and may herniate Congenital or acquired Headaches, neck pain, tinnitus, nausea, facial pain, muscle weakness, sleep apnea, difficulty swallowing, impaired co-ordination, rapid heart beat, dizziness, fainting, thirst, chronic fatigue, paralysis in severe cases = increased pressure in brain because they can’t circulate the CSF through the brain causing significant impairment of brain function.
60
What are the ocular features of Arnold-Chiari Malformation?
Ocular features: - Various types of nystagmus but typically downbeat - Impaired pursuit - Impaired OKN - Concomitant ET - Divergence paralysis - Skew deviation - INO
Year 3 Strab
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