Brainstem 3: Brainstem Syndromes

Question 1

For what two reasons, broadly, should you consider the brain stem when localizing a lesion?

Answer 1

Cranial nerve deficits

Cerebellar dysfunction.

Question 2

When do you know the lesion is in the brainstem?

Answer 2

Crossed hemiparesis with CN weakness (or ataxia) on one side, and lower body weakness on the opposite side.

Question 3

Having both of which 2 signs should make you think a lesion is localized around the brainstem (in the subarachnoid space)?

Answer 3

Multiple CNs involved

No crossed motor’/sensory signs in extremities

Question 4

50 year old diabetic man, sudden onset of left arm/leg weakness and horizontal diplopia. Decreased vibration sense on left. Can’t fully abduct right eye. Where is the lesion?

Answer 4

Must be hitting near CN VI nucleus or fibers (which are in the pons), must be hitting right corticospinal tract (which are ventral). No loss of pain/temp sensation suggests spinothalamic tract not hit (which are lateral) Thus… this is a lesion to the medial ventral pons.

Question 5

How can you get CN deficits from a ventral lesion?

Answer 5

The CN fibers run out ventrally from their nuclei (except, notably, for CN IV).

Question 6

What’s the best way to tell if a brain stem lesion is ventral or not?

Answer 6

If the corticospinal tract is lesioned, it’s got to be ventral.

Question 7

What structures help with medial-lateral localization of a lesion? (name 4)

Answer 7

Medial structures: Corticospinal tract, medial lemniscus

Lateral structures: spinothalamic, sympathetic neurons

Question 8

5 broad categories of things that can lesion the brain stem?

Answer 8

Vascular (infarct or hemorrhage), inflammation/demyelination, tumors, metabolic disorders, herniation

Question 9

What blood vessels supply the medial (both ventral and dorsal) of the brainstem?

Answer 9

Paramedian arteries from the anterior spinal a.

Question 10

What blood vessels supply the ventral lateral surface of the brainstem?

Answer 10

Short circumferential arteries coming off the basilar a. (some of these are the pontine aa.)

Question 11

What blood vessels supply the dorsal lateral surface of the brainstem? (specify medulla, pons, midbrain)

Answer 11

Long circumferential arteries:
Medulla: PICA
Pons: AICA
Midbrain: SCA

Question 12

50 year old man with 1 wk progressive bilateral arm and leg ataxia (can’t walk) with diplopia. Neither eye can be adducted when looking left or right. Where is the lesion?

Answer 12

No weakness, so it’s not ventral. Patient has bilateral internuclear opthalamoplegia (INO) due to lesion of the MLFs -> bilateral dorsal pons lesion. Ataxia from hitting crossing fibers. Note that an isolated cerebellar lesion wouldn’t cause the eye symptoms.

Question 13

What is an INO? Primary symptom? Cause?

Answer 13

Internuclear opthalmoplegia - when looking to side horizontally, the far eye fails to adduct.
Presents as diplopia.
Lesion to MLF ipsilaterally to eye that won’t adduct.

Question 14

When the patient is looking left, what will you see when the patient has…
Left CN VI lesion?
Left Internuclear opthalmoplegia (INO)?
Left VI nucleus lesion?

Answer 14

CN VI lesion: Left eye won’t abduct
INO (i.e. lesion to MLF): Right eye won’t adduct.
VI nucleus: neither eye will turn to the left

Question 15

Mechanism of INO? (2 things)

Answer 15

Demyelination - when bilateral or in young patient

Infarction - in older person

Question 16

70 year old man with 2mo progressive facial weakness and horizontal diplopia. No weakness or numbness. No ataxia. Right sided Bell’s Palsy. Can’t abduct left eye. Where is the lesion?

Answer 16

Multiple CNs affected, no weakness or numbness suggests lesion is outside brainstem, probably subarachnoid. (Turns out it was focal inflammation on opposite sides… which is weird, but happens)

Question 17

43 year old man, 2 years left hearing loss, left facial weakness. Lethargy and vomiting. Deaf in left ear. Decreased pain on left face. No weakness or sensory loss in legs and face. Impaired left corneal reflex (eye doesn’t closed when touched).

Answer 17

Left CN V, VII, and VIII deficits. Because auditory innervation is bilateral once in the CNS, unilateral hearing loss suggests lesion to CN VIII. Localization: Outside brainstem on left side at the level of the pons. (it was big tumor there, pushing on brainstem)

Question 18

70 year old man with left arm and leg weakness and diplopia. Severe right ptosis and eye stuck “down and out.”

Answer 18

Crossed signs -> midbrain. Must involve ventral areas. Hitting right CN III fibers and right corticospinal tract. Localization: Right ventral midbrain.

Question 19

What causes a jaw deviated to the left when open?

Answer 19

Lesion to left CN V or its motor nucleus.

Question 20

What does a palate drooping on the left tell you?

Answer 20

Left 10th (and probably also 9th) CN deficit - unopposed activity of the right levator velli palatini.

Question 21

What does left tongue atrophy / tongue deviating to the left tell you?

Answer 21

CN XII deficit. (recall CN XII makes the tongue stick out)