25 - Lesions I Flashcards
What is a syndrome?
A disorder characterized by a set or pattern of symptoms
A “symptom complex”
When referring to a lesion, what does “ipsilateral deficits” mean?
The deficits appear ipsilateral (on the same side) as the lesion
When referring to a lesion, what does “contralateral deficits” mean?
Deficits that appear contralateral (on the opposite side) as the lesion
Paresis
Weakness (partial paralysis)
Hemiparesis
Weakness of one side of the body (face, arm, leg)
Palsy
Weakness or no movement
Paralysis
No movement
Hemiplegia
No movement on one side of the body (face, arm, leg)
What is Weber Syndrome?
A medial midbrain syndrome that occurs due to a lesion in the rostral (upper) midbrain (1) basis
What are the two main effects of Weber Syndrome?
- Ipsilateral oculomotor nerve palsy
- Contralateral hemiparesis
This means that in a patient with Weber Syndrome, you will see a weakness or inability to move the oculomotor nerve (little to no eye movement) on the same side as the lesion and a weakness of the skeletal muscles of the face, arm and leg on the opposite side of the body (contralateral to the lesion)
If the lesion was on the left, what would be the effect on the oculomotor nerve?
Oculomotor nerve palsy on the LEFT
If the lesion was on the left, what would be the effect on the lateral pterygoid?
A muscle of mastication
Weak lateral pterygoid on the RIGHT
If the lesion was on the left, what would be the effect on the facial muscles?
Weak facial muscles on the LOWER RIGHT (upper muscles have “back up” innervation
If the lesion was on the left, what would be the effect on the musculus uvulae?
The musculus uvulae, which lies entirely within the uvula, shortens and broadens the uvula
Remember that the musculus uvulae pulls the uvula towards itself
Weak musculus uvulae on the RIGHT
This means the uvula would deviate towards the left side
If the lesion was on the left, what would be the effect on the genioglossus?
Muscle that functions in sticking out the tongue
Weak genioglossus on the RIGHT side
Since the genioglossus pushes the tongue toward the midline to protrude from the mouth, a weakness on the right side means the left genioglossus will overpower and the tongue will deviate to the right
If the lesion was on the left, what would be the effect on the extremities?
Weak extremities on the RIGHT side
We know that Weber Syndrome (medial midbrain syndrome) is due to a lesion in the rostral (upper) midbrain (1), but what would specifically cause this lesion?
Occlusion of vessels supplying the medial portions of the midbrain
Which vessels supply the medial portions of the midbrain?
- Branches of the posterior cerebral artery (PCA)
- Top of the basilar artery
A vascular lesion involving the above vessels or their branches that infiltrate the rostral (upper) midbrain basis may result in lack of oxygen to major nerve fibers
Which three sets of nerve fibers are affected due to an occlusion of the PCA or top part of the basilar artery?
- Exiting root of the oculomotor nerve
- Corticonuclear fibers
- Corticospinal fibers
What type of fibers are found in the exiting root of the oculomotor nerve?
GSE and GVE fibers
GSE - general somatic efferent (skeletal muscle innervation)
GVE - general visceral efferent (autonomic fibers to smooth muscle)
What does the oculomotor nerve innervate?
The IPSILATERAL eye
What will occur if the oculomotor nerve is damaged as it exits the midbrain?
- Ipsilateral paralysis of the levator palpebrae superioris (LPS) resulting in ptosis
- Ipsilateral paralysis of all other extraocular muscles except LR6SO4
- Eye cannot move medially or vertically
- Eye is deviated down and out (lateral strabismus)
- Patient will experience diplopia
- Ipsilateral dilation of the pupil (mydriasis) which remains in this fixed, dilated position
- Lens is flat
What do we call the paralysis of the ipsilateral eye muscles innervated by the oculomotor nerve?
Ipsilateral oculomotor nerve palsy
Which corticonuclear fibers will be affected in Weber syndrome?
The fibers that lie in the basis pedunculi (cerebral peduncles) prior to their distribution
A lesion that damages teh corticonuclear (UMN) tract in the rostral (upper) midbrain (1) will damage what four nuclei?
- Trigeminal motor nucleus
- Facial nucleus
- Nucleus ambiguus
- Hypoglossal nucleus
Describe the trigeminal motor nucleus
- Located in the midpons
- Receives bilateral UMN projections, except for the LMNs that innervate the lateral pterygoid muscle
- The lateral pterygoid muscle receives only contralateral projections
Describe the deficits that will occur with a lesion to the corticonuclear (UMN) tract on the LEFT side in relation to the trigeminal motor nucleus
- Contralateral weakness and paralysis of the lateral pterygoid muscle
- RIGHT lateral pterygoid will be affected and will be weak
The jaw will deviate to the right side (weak side) on protrusion of the jaw
Describe the facial nucleus
- The upper half of the facial nucleus receives bilateral UMN projections
- The lower half of the facial nucleus receives contralateral UMN projections
Describe the deficits that will occur with a lesion to the corticonuclear (UMN) tract on the LEFT side in relation to the facial nucleus
- Contralateral weakness and paralysis of the muscles of the lower face
- RIGHT LOWER facial muscles will be affected and will show weakness/paralysis
Describe the nucleus ambiguus
- Receives bilateral (primarily contralateral) UMN projections
Describe the deficits that will occur with a lesion to the corticonuclear (UMN) tract on the LEFT side in relation to the nucleus ambiguus
- Contralateral weakness and paralysis of the musculus uvulae will occur
- The RIGHT musculus uvulae will be affected, uvula will be “pulled” to the innervated (intact) side and will deviate to the LEFT when saying “ahhhh”
Describe the hypoglossal nucleus
- Receives bilateral UMN projections, except for the LMN’s that innervate the genioglossus, which receives only contralateral UMN projections
Describe the deficits that will occur with a lesion to the corticonuclear (UMN) tract on the LEFT side in relation to the hypoglossal nucleus
- Contralateral weakness/paralysis of genioglossus muscle will occur to the RIGHT side of tongue
- The innervated/intact side “pushes” toungue to deviate toward the weak side (to the right) upon protrusion
- The tongue will deviate to the RIGHT side
Describe the corticospinal fibers affected from Weber Syndrome
- Corticospinal fibers in the basis pedunculi (cerebral peduncles) ABOVE the pyramidal decussation (crossing) are affected by Weber Syndrome
What is the result of a lesion affecting the corticospinal fibers prior to decussation?
Contralateral weakness (hemiparesis) of the extremities
What is Claude Syndrome?
A central midbrain syndrome that occurs in the tegmentum of the midbrain
What are the overall effects of Claude syndrome?
- Ipsilateral oculomotor nerve palsy
- Contralateral ataxia and tremor of cerebellar origin
Occlusion of which vessels will result in Claude syndrome?
Occlusion of vessels supplying the central portions of the midbrain
- Branches of the posterior cerebral artery (PCA)
- Top of basilar artery
There are three structures that are affected by a Claude syndrome lesion and are responsible for the resulting deficits. What are they?
1 - Oculomotor nerve fasicles
2 - Red nucleus
3 - Cerebellothalamic fibers
Which eye do the oculomotor nerve fascicles innervate?
The oculomotor NERVE innervates the IPSILATERAL eye
What deficits result from damage to the oculomotor nerve fasicles?
- Ipsilateral paralysis of the levator palpebrae superioris (LPS) resulting in ptosis
- Ipsilateral paralysis of all extraocular muscles (ipsilateral oculomotor nerve palsy) except LR6SO4
- Eye cannot move medially or vertically
- Eye is deviated down and out (lateral strabismus)
- Diplopia is experienced by patient
- Ipsilateral dilation of the pupil (fixed mydriasis)
- Lens is flat
What is the red nucleus?
A structure in the rostral midbrain involved in motor coordination
There is nothing listed on the hand out in terms of deficits, but the red nucleus is damaged in Claude Syndrome
What are cerebellothalamic fibers?
The cerebellum gives rise to a group of OUTPUT fibers called cerebellothalamic fibers
What is the initial path of the cerebellothalamic fibers?
They exit the cerebellum and ascend to the midbrain via the superior cerebellar peduncle (SCP) at the level of the inferior colliculus
Where do the cerebellothalamic fibers decussate?
When they reach the caudal midbrain, these fibers decussate in the decussation of the superior cerebellar peduncle (SCP) at the level of the inferior colliculus
Where do the cerebellothalamic fibers go from here?
From here, these fibers continue their ascent to the thalamus which in turn projects to the motor cortex
What does the motor cortex control?
Movement of the opposite side of the body
With a lesion that is ROSTRAL to the superior cerebellar peduncle (SCP) decussation on the RIGHT, what will be damaged?
Cerebellothalamic fibers that are carrying information from the contralateral (LEFT) cerebellum
What deficits will result from a lesion on the right side, rostral to the SCP?
Contralateral (LEFT) ataxia and tremor of cerebellar origin
What is Benedikt Syndrome?
A medial midbrain lesion combined with a central midbrain lesion
What is the overall result of Benedikt syndrome?
- Ipsilateral oculomotor nerve palsy
- Contralateral hemiparesis
- Contralateral ataxia, tremor and involuntary movements
The occlusion of which vessels results in this damage
- Branches of the posterior cerebral artery (PCA)
- Top of basilar artery
There are six structures that are affected by these lesions
1 - Oculomotor nerve fascicles 2 - Corticonuclear fibers 3 - Corticospinal fibers 4 - Red nucleus 5 - Cerebellothalamic fibers 6 - Substantia nigra
What are the deficits that occur with damage to the oculomotor nerve fascicles?
- Ipsilateral paralysis of the levator palpebre superioris (LPS causing ptosis
- Ipsilateral paralysis of all extraocular muscles (ipsilateral oculomotor nerve palsy) except the LR6SO4
- Eyes cannot move medially or vertically
- Eye is deviated down and out (lateral strabismus)
- Patient experiences diplopia
- Ipsilateral dilation of the pupil (fixed mydriasis)
- Lens is flat
What deficits occur with damage to the corticonuclear fibers? Where in the tract does the damage occur?
The corticonuclear fibers are in the basis pedunculi (prior to their distribution)
CONTRALATERAL weakness and paralysis of the following muscles:
- Lateral pterygoid muscle
- Muscles of the lower face
- Musculus uvulae
- Genioglossus
What deficits occur with damage to the corticospinal fibers? Where in the tract does the damage occur?
The corticospinal fibers are in the basis pedunculi (cerebral peduncles) and are damaged prior to their distribution
The result is contralateral weakness (hemiparesis) of the extremities
What is the red nucleus?
A structure in the rostral midbrain involved in motor coordination
There is nothing listed on the hand out in terms of deficits, but the red nucleus is damaged in Claude Syndrome
What is the origin of the cerebellothalamic fibers?
Cerebellum
Where do the cerebellothalamic fibers exit the cerebellum?
Superior cerebellar peduncle
What is the path of the cerebellothalamic fibers?
They ascend to the caudal midbrain where they decussate in the decussation of the superior cerebellar peduncle, located at the level of the inferior colliculus
What occurs with a lesion to the cerebellothalamic fibers ROSTRAL to the superior cerebellar peduncle decussation?
Does this mean before or after the decussation? I’m guessing before because symptoms are contralateral.
Contralateral ataxia and tremor (of cerebellar origin) in the paretic (weak) limbs
Remember ataxia is lack of voluntary coordination of muscle movements
Describe the relationship that the basal ganglia (including the substantia nigra) has on movement
- Output from the RIGHT basal ganglia (including the substantia nigra) is projected to the RIGHT thalamus
- The right thalamus in turn projects to the RIGHT motor cortex
- The right motor cortex controls movement of the LEFT side of the body
So… movement of the left side of the body is influenced by the right basal ganglia (including the substantia nigra)
What is the deficit that occurs with damage to the substantia nigra?
Contralateral involuntary movements occur (damaged substantia nigra)
Compare the motor cortex, basal ganglia and cerebellum in terms of whether they control movement on the opposite side or ipsilateral side of the body
Motor cortex - opposite side of body
Basal ganglia - opposite side of body
Cerebellum - ipsilateral side of body
Other than an arterial occlusion, what else can cause a midbrain lesion?
Demyelinating disease
What’s an example of a demyelinating disease?
Multiple sclerosis
If there is a demyelinating lesion in the caudal (lower) midbrain at the level of the inferior colliculus, where will this be in relation to the decussation of the superior cerebellar peduncle (SCP)?
ROSTRAL to the decussation
A demyelinating lesion of the caudal midbrain at the level of the inferior colliculus, rostral to the decussation of the SCP will cause damage to which structures?
- Cerebellothalamic fibers
- Trochlear nucleus
- Medial longitudinal fasiculus
If there is a demyelinating lesion of the caudal midbrain at the level of the inferior colliculus, rostral to the decussation of the SCP on the LEFT side, what will be the effect on the cerebellothalamic fibers?
The cerebellothalamic fibers (from the superior cerebellar peduncle) will cause deficits in the RIGHT limbs
- Intention tremor
- Dysmetria
- Dysdiadochokinesia
Intention tremor
- A tremor that increases in amplitude as the individual approaches the endpoint of deliberate and visually guided movement
- An intention tremor is usually perpendicular to the direction of movement
So pretty much, you reach for something and when your hand gets close to the object you’re reaching for, the tremor gets stronger and jerks your hand back away from the object you’re reaching for.
Dysmetria
A lack of coordination of movement typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye
AKA “past pointing”
Dysdiadochokinesia
Inability to perform rapid alternating movements such as rapid pronation and supination of the forearm (SPAL test)
If there is a demyelinating lesion of the caudal midbrain at the level of the inferior colliculus, rostral to the decussation of the SCP on the LEFT side, what will be the effect on the trochlear nucleus?
The LEFT trochlear nucleus will be affected, but the left trochlear nucleus innervates the RIGHT SO4
The RIGHT eye will be deviated upward (hypertropic) and slightly outward (extorted)
If there is a demyelinating lesion of the caudal midbrain at the level of the inferior colliculus, rostral to the decussation of the SCP on the LEFT side, what will be the effect on the medial longitudinal fasciculus (MLF)
LEFT internuclear ophthalmoplegia (INO) will occur
THe LEFT eye does not turn medially to gaze to the right
Larger infarcts that involve the midbrain reticular formation will cause…
Impaired consciousness
What are some examples of impaired consciousness that results from an infart involving the midbrain reticular fomation?
- Somnolence
- Delirium
- Hallucinations
What is Perinaud Syndrome?
Vertical gaze paralysis that occurs with a lesion in the dorsal rostral midbrain
(the back of the upper part of the midbrain (1))
What structures are involved in Perinaud syndrome?
- Vergence center
- Oculomotor nucleus
- EW-N
What is the resulting deficit for damage to the vergence center in Perinaud syndrome?
The vergence center is located in a pretectal area just rostral to the superior colliculus
A deficit that results from damage to the vergence center is the inability to move the eyes vertically (up and down)
What is the resulting deficit for damage to the oculomotor nucleus in Perinaud syndrome?
We’ve been through this many times… But here you go:
- Ipsilateral paralysis of the levator palpebre superioris (LPS causing ptosis
- Ipsilateral paralysis of all extraocular muscles (ipsilateral oculomotor nerve palsy) except the LR6SO4
- Eyes cannot move medially or vertically
- Eye is deviated down and out (lateral strabismus)
- Patient experiences diplopia
- Ipsilateral dilation of the pupil (fixed mydriasis)
- Lens is flat
What is EW-N?
Edinger–Westphal nucleus
AKA accessory oculomotor nucleus
What is the Edinger–Westphal nucleus responsible for?
The Edinger–Westphal nucleus (accessory oculomotor nucleus) are the parasympathetic pre-ganglionic neurons that originate the oculomotor nerve. It supplies the iris sphincter muscle and the ciliary muscle.
