Cranial Nerve Lesions - 62

Front 1

1. Describe the role of gaze centers?

2. Describe pontine gaze centers?

3. Where do the fibers of the pontine gaze centers cross?

1. horizontal gaze

2. pontine gaze

Back 1

1. Conjugate eye movements will be horizontal or vertical. Eye movements are controlled by the conjugate gaze centers.

2. The important gaze center for horizontal gaze is paramedian pontine reticular formation which is in the pons and that controls the horizontal gaze. The voluntary system for horizontal gaze is frontal eye field. This is area 8 aka middle frontal gyrus. Looking to the left activates the right center which in turn activates the left pontine gaze center. When the left pontine gaze center is activated, the left eye moves out so the left pontine gaze center is para abducens and when activated it will stimulate the 6th nerve on the same side so the left side will abduct.

3. The pontine gaze center have fibers that cross the median longitudinal fasciculus. The PPRF controls the contralateral medial rectus nucleus so the right eye will adduct and the left will abduct.

-Stimulating the gaze center on the left, both eyes will go to the left side. Ipsilateral gaze is when you stimulate the pontine center. There is contralateral gaze when you excite the frontal eye field.

The brainstem is your PPRF.

Front 2

1. What will happen if there is a lesion on the left CN VII?

2. What will happen if there is a sensory or afferent lesion on the 5th cranial nerve?

Back 2

1. A lesion on the left 7th nerve will not allow for blinking on the left side, but there is no absent cornea reflex because the opposite side will blink. If there is an efferent problem on the left side, the left eye will not blink but the right side will blink because there is no lesion to the 5th afferent nerve.

2. There will be an absent cornea reflex if there is a sensory or afferent lesion on the 5th so there will be an absent cornea reflex period. With just a lesion on CN 7 you will not have a blink reflex on one side.

The 7th supplies only one side of the face. The trigeminal on one side goes to both 7th nerves.

Front 3

What are some symptoms of CN VII problem?

Back 3

A peripheral 7th nerve problem gives inability to frown, no wrinkling on the forehead, and in the lower part there will be a flattening of the nasal fold, a drooping at the angle of the mouth, some drooling and difficulty puffing the cheek.

The 7th nerve has lower and upper motor weakness

Front 4

1. Describe the corticobulbar pathway supply?

2. What happens if there is a unilateral corticospinal corticobulbar lesion?

Back 4

1. The corticobulbar is the upper motor neuron pathway to CN motor nuclei. Corticobulbar supplies bilateral cranial motor nuclei and corticospinal is unilateral contralateral. 5, 7, 9, 10, 11 and 12 are important cranial motor nuclei in the corticobulbar tract. 5 and 7 are in the pons. 9, 10, 11 and 12 are in the medulla. The bulbar is made in reference to the medulla.

2. There will be no cranial motor manifestations because of the bilateral supply.

Front 5

What is the result of a lesion of the upper motor neuron pathway of the cortico-spinal/corticobulbar system?

Back 5

The lower side of the face will be weak on the contralateral side to the lesion. The upper part of the 7th is important because of eye closure. If there is a corticobulbar lesion, you can still close the eye because the upper half is still able to close the eye. However, the lower part of the face only gets unilateral contralateral supply from the corticospinal tract.

- This is an upper motor neuron type of weakness also called supranuclear or central facial weakness.

Front 6

1. What happens if there is a lesion on the right pons?

2. What happens if there is a right side lesion of the pons on the corticospinal tract?

3. Effect of lesions of the CST at the brainstem and above the brainstem?

4. Effect of lesion on the CST below its crossing?

Back 6

The right side of the face will be weak so it is an ipsilateral deficit. You will see a lower motor neuron weakness also called a peripheral or intranuclear weakness.

2. It will give you a weakness on the left side of the body. The crossing of the CST is below the pyramid at the junction of the medulla and the spinal cord.

3. Any lesion at the brainstem and above the brainstem of the CST will give you a clinical manifestation on the contralateral side of the body.

4. Any lesion on the CST below the crossing will give you weakness on the ipsilateral side of the body.

Front 7

How is the 4th cranial nerve different from the other cranial nerves?

Back 7

All CN are ipsilateral with one exception and that is the 4th nerve. It is the only one that decussates after its origin in its nucleus.

-The CN lesions will have a clinical manifestation ipsilateral to the lesion but at the level of the CST in the case of the lesion being at the brainstem or above the brainstem, the clinical manifestation will be contralateral.

Front 8

Where is this lesion if a patient presents to you with a facial weakness on the right side and a hemiparesis on the left side?

Back 8

The lesion is in the brainstem at the level where that cranial nerve is originating and at the same side where that cranial nerve is manifested at. Lesion in the brainstem means that it is a lower motor neuron weakness. This is in terms of the cortico-spinal tract.

Front 9

Where is the lesion if there is a right CN 7 and a left hemiparesis?

Back 9

this is a cross manifestation so the lesion is in the brainstem at the right side of the pons since the right CN 7 is involved and CN 7 exits the brainstem in the cerebelloPONtine angle.

NOTE:

CN 6 originates at the level of the pons. CN 3 is at the level of the midbrain. CN 12 is at the level of the medulla.

Front 10

1. Discuss why CN 7 has 2 types of weaknesses?

2. Demonstrate how a lesion in CN 7 can lead to an upper motor neuron weakness or a lower motor neuron weakness?

Back 10

The 7th has two types of weaknesses because the upper side of the face has bilateral supply but the lower side of the face has unilateral contralateral/corticobulbar supply.

2. . If there is an upper motor neuron weakness, the weakness will be contralateral to the lesion and this will only affect the lower part of the face. The hemiparesis in the patient will be on the same side of the CST where the facial weakness is and this will be contralateral to the lesion (QUESTION HER).

If there is a right facial weakness on the left hemiparesis IT IS A LOWER MOTOR NEURON WEAKNESS (SOUNDS CONTRADICTORY).

Front 11

Describe effect of lesion of CN 8?

Back 11

Mostly cause vertigo (dizziness, loss of balance) this is seen subjectively in the patient.
-What is seen objectively in the patient is nystagmus. Nystagmus is a jerky eye movement with a fast and a slow component. The nystagmus is always in the direction of the fast component. If nystagmus is seen to the right then the fast component is seen to the right. The fast phase is your correctional higher component.

Front 12

What will happen if there is a lesion in the innervation of the miscles of mastication?

Back 12

With the muscles of mastication, if you open the jaw the jaw will protrude to the side of the lesion. The tongue will not be able to push to the opposite side because this is a lower motor neuron weakness (ONCE AGAIN SOUNDS CONTRADICTORY). Over time with that same tongue, you will see atrophy and fasciculations. These are signs of lower motor neuron damage.

Front 13

1. What does it tell you if there is a facial weakness on the same side as the hemiparesis ?

2. What does it tell you if your facial weakness is on one side and the hemiparesis is on the other side?

Back 13

1. If there is a facial weakness on the same side as the hemiparesis the lesion has to be contralateral.

2. If your facial weakness is on one side and the hemiparesis is on the other side, that is a cross manifestation and the lesion is in the brainstem on the same side as the CN and the CN manifestation has to be lower motor neuron.

The side that will not elevate is your weakside.

Front 14

1. What is happening if a patient cannot move both eyes towards right or left?

2. Describe the 1 ½ syndrome ?

Back 14

1. This is a gaze palsy. Gaze palsy involves the PPRF. The action of the right pontine center is to pull both eyes towards the right. If both eyes are not pulling to the right, there is a problem in the right pons.

2. If a patient looks to the left and only the left side pulls out, the gaze center on the left gives the signal to the left 6th nerve but the info to the right 3rd nerve is gone because the pathway to the right Medial longitudinal fasciculus is gone. There is no lesion to the 3rd nucleus on the right side because convergence is preserved. The medial rectus can move on convergence but it cannot move on horizontal gaze. This is called the 1 ½ syndrome which means only half an eye is moving and that is the lateral rectus on the left.

- On the right side there is hardly abduction and hardly adduction. On the left side there is no adduction because the gaze center is gone. The pontine center is gone and the MLF pathway is gone on the right side which can give you paralysis of gaze to the right side which won’t allow adduction of the right eye. This is an ipsilateral gaze and ipsilateral MLF pathway.

Front 15

Name the location of motor CN 5, CN 6, CN 7, CN 8, CN 9, CN 10, and sensory V?

Back 15

5, 6 and 7 are in the pons. The descending tract of the trigeminal nucleus is in the medulla. 8th nerve is at the ponto-medullary junction. 8, 9, 10, and sensory V are all in the lateral medulla.

ASIDE:

Horner Syndrome is involves the sympathetic tract in the lateral medulla. . If you see a significant facial sensory loss, that is primarily the lateral medulla.

Front 16

1. Where are the location of the signs of cerebellar lesions?

2. What is the only contralateral deficit in PICA syndrome?

3. What is the only crossed tract in the lateral medulla?

Back 16

1. The location of the signs of cerebellar lesions are ipsilateral to the lesion.

2. The only contralateral deficit in PICA syndrome is the contralateral pain and temperature.

3.The only crossed tract in the lateral medulla is the lateral spinothalamic tract.

ASIDE:
Scanning speech involves the cerebellar.

Front 17

1. In terms of MLF and PPRF, what is the importance of the frontal lobe and ipsilateral gaze?

2. If a patient is asked to look to the left, what will the PPRF do?

Back 17

1. In terms of the MLF and PPRF, the frontal lobe is for ipsilateral gaze and the pprf is for ipsilateral gaze.

2. if a patient is asked to look to the left, the PPRF on the left side is next to CN 6 which will cause the movement of the lateral rectus causing abduction of the left eye. At the same time, the PPRF acts via the MLF to the contralateral side and the MLF acts on the medial rectus of the right eyeto look to the left. Case and point, PPRF is for ipsilateral gaze and the frontal cortex is for contralateral gaze. This is for voluntary horizontal eye movements.

Front 18

1. With the exception for CN 7, any lesion at the level of the brainstem or above the brainstem leads to what?

2. In terms of CST, a lesion above or at the brainstem, will lead to what?

3. Describe patients with pain and temperature loss?

Back 18

1. With the exception for CN 7, any lesion at the level of the brainstem or above the brainstem gives a lower motor neuron deficit.

2. . In terms of CST, a lesion above or at the brainstem, will give contralateral deficit but below the brainstem gives ipsilateral deficit.

3. For the patient with the pain and temperature loss, the loss is ipsilateral because of the first order neurons that are affected and these first order neurons have not crossed.

Front 19

Describe the jaw jerk reflex and the muscles involved? What type of motor neuron weakness is it?

Back 19

With the jaw reflex, CN V acts on the pterygoid muscles. They both push each other out so when there is a lesion lets say to the right side, the deviation will be to the right because when the jaw is pushed out, the only muscle that is pushing is the left side of the jaw but the right side cannot act back. That is why in the long run, you will see atrophy of the affected side. This is a lower motor neuron weakness.