Principles of Brainstem Disease

Question 1

What are the three main components of the brainstem (and their embryonic names)?

HINT- think STY

Answer 1

midbrain- mesencephalon
pons- metencephalon
medullar oblongata- myelencephalon

Question 2

Which nerves run through the brainstem?

Answer 2

CN III- XII
with 3 & 4 in the midbrain
5 in the pons
and 6-12 in the medulla oblongata

Question 3

Which cranial nerves have parasympathetic function?

[think slowing down, relaxing etc.]

Answer 3

CN III, VII, IX and X
(thats oculomotor, facial, glossopharyngeal and vagus)

Question 4

Is the brainstem an ipsi or contralateral system?

Answer 4

Ipsilateral

Question 5

What are some general clinical signs of Brainstem dysfunction?

Answer 5

comatose (brainstem= consciousness), decerebrate rigidity, paresis in all limbs or ipsilateral to the side of the lesion, absent postural reactions in limbs ipsilateral to the lesion, CN III-XII deficits. cardiorespiratory abnormalities (because brainstem also controls CVS)

Question 6

Why do brainstem lesions present signs of decerebrate rigidity?

Answer 6

Lesions in the midbrain - causes LMNs in the limbs, trunk, neck to be released from UMN inhibition

Question 7

What three brainstem motor tracts are responsible for gait generation?

Answer 7

Rubrospinal tract ( red nucleus in the midbrain)
Pontine (aka Medial) Reticulospinal Tract (from the pons)
Reticulospinal Tract (from the medulla oblongata)

Question 8

How would a midbrain lesion affect the motor function of the eye and why?

Answer 8

Affects CN III (Oculomotor) which innervates the extraocular muscles (movement of the globe medially) and the levator superioris muscle (elevates the eyelid)
so lesion causes lateral strabismus and ptosis (eyelid drooping)

Question 9

Does CN III contribute parasympathetically to the eye? How? And what happens to this in cases of brainstem lesions?

Answer 9

Yes- in charge of pupil constriction so brainstem lesion will cause Mydriasis & Aniscoria

Question 10

Describe the PLR and Menace responses for an animal with a brainstem lesion affecting CN III.

Answer 10

no PLR as parasympathetic function impaired
Menace response present as Optic Nerve & Facial nerve still intact

Question 11

What is the motor function of CN IV in regards to the eye?
What happens to the eye when there is a lesion on this nerve?

Answer 11

CN IV function rotates the medially so lesions can cause lateral extortion of the pupil
[like the pupil is being dragged laterally at the top]

Question 12

What is the difference in outcomes of a lesion of the trochlear nerve and the trochlear nucleus?

Answer 12

lesion at nerve causes ipsilateral extortion of the pupil
lesion at the nucleus causes contralateral extortion of the pupil
[this is because the nerve emerges from the right side to innervate the structures on the left]

Question 13

What is the role of the Abducens nerve in the motor function of the eye and what happens when there is a lesion here?

Answer 13

Abducens pulls the eye laterally so lesion causes medial strabismus and also plays a role in retracting the globe so lesion could affect the menace response

Question 14

What causes a CONGENITAL medial strabismus?

Answer 14

Genetics involving increased decussation (crossing over) at the optic chiasm and cross eyed appearance but no visual deficits

Question 15

What nerve would a lesion in the pons of the brainstem affect?

Answer 15

CN V - Trigeminal

Question 16

A lesion in the pons, affecting the sensory aspect of the Trigeminal nerve would cause…

Answer 16

reduced facial sensation
reduced palpebral and corneal reflex

Question 17

What causes Neuroparalytic Keratitis?

Answer 17

Lesion of the ophthalmic branch of the trigeminal that is responsible for reflex tearing- leads to corneal drying and ulcer formation

Question 18

What is the motor function of the Trigeminal Nerve and what happens if there is a lesion affecting this?

Answer 18

Muscles of mastication & jaw closure- lesion causes atrophy of the masticatory muscles

Question 19

Would a lesion in CN V affect the ear at all?

Answer 19

Yes- CN V is innervates the tensor tympani muscle which associates with the malleus to dampen loud noises to protect the ear- lesions in CN V may cause an increased sensitivity to noise

Question 20

What would a lesion of the facial nerve result in? (3)

Answer 20

Facial Asymmetry
Pseudo-hypersalivation
Lack of blink

Question 21

How would the clinical signs of a CN VII lesion differ in small animals and large animals?

Answer 21

SA- droopy face, subtle ptosis
LA- deviation of the nose to the unaffected side (think their nose is more cartilaginous than SA), ear droops, noticeable Ptosis

Question 22

Can ear disease affect the face? And why?

Answer 22

Facial nerve runs adjacent to tympanic bulla so disease of the middle ear is a common cause of facial paralysis

Question 23

Which nerves are affected by lesions in the Medulla Oblongata and what does this present as?

Answer 23

CN IX, X
Glossopharyngeal & Vagus
Presents as Dysphonia (voice changes) & stridor (high pitched respiratory noise), laryngeal paralysis, megaoesophagus

Question 24

What are the two most common neuromuscular diseases that present with stridor & dysphonia?

Answer 24

Geriatric onset laryngeal paralysis polyneuropathy complex (GOLPP)- this can also affect the sciatic nerve
Myasthenia Gravis

Question 25

What would a lesion in the medulla oblongata affecting CN XII present as?

Answer 25

tongue atrophy and deviation of the tongue to the affected side

Question 26

Enlarged pupils (Mydriasis) is a sign of what system damage?
What about Miosis?

Answer 26

Enlarged- sympathetic (think sympathy- dilation etc.)
Miosis- Parasympathetic

Question 27

What are the most common causes of Aniscoria?

Answer 27

Horner’s syndrome (Miosis)
Uveitis (Miosis)
Glaucoma (Mydriasis)
Topical mydriatic (drugs- atropine)

Question 28

What do we mean when we say the sympathetic innervation of the eye is a three neuron pathway?

Answer 28

Hypothalamus > 1st order neurons in spinal cord > 2nd order neurons in the thoracic trunk > 3rd order neurons in the inner ear cavity > sympathetic nerve innervation of pupils and smooth muscle