Exam #3: Lesions I Flashcards
What three structures are part of the cerebral peduncle in the rostral midbrain?
1) Tegmentum
2) SN
3) Basis Pedunculi
What does the MLF connect?
CN III, IV, VI in the caudal midbrain
What is the only CN to cross in the midbrain?
Trochlear nerve
Where is the decussation of the SCP?
Caudal midbrain
What artery supplies the corticospinal & corticonuclear tracts in the midbain basis pedunculi?
PCA
What arteries supply the midbrain?
Branches of the PCA
Superior Basilar a.
What specific artery supplies the corpora quadrigemi?
Quadrageminal a. which is a branch of the PCA
What is the eponym for Medial Midbrain Syndrome?
Weber Syndrome
What is the eponym for Central Midbrain Syndrome?
Claude Syndrome
What is the eponym for Medial Midbrain + Central Midbrain Syndrome?
Benedict Syndrome
What is the general pattern of midbrain lesions?
- Oculomotor nerve palsy IPSILATEAL
- All of the other deficits (hemiparesis) are CONTRALATEARAL
Where is the lesion in Medial Midbrain Syndrome (Weber)?
Rostral Midbrain Basis i.e. the base (ventral) portion of the rostral midbrain
What structure are involved in Medial Midbrain Syndrome?
Oculomotor n.
Corticospinal
Corticonuclear
What is the presentation of Medial Midbrain Syndrome in relation to the eye? Explain the presentation to the associated muscles that are paralyzed b/c of the lesion.
IPSILATERAl CN III palsy=
- Ptosis (levator palpebrae superioris)
- Lateral strabismus/ horizontal diplopia (medial rectus + LR & SO)
- Vertical diplopia (superior & inferior rectus)
- Mydriasis (PNS sphincter pupillae)
- No accomodation of the lens (PNS ciliary muscle)
With a CN III lesion on the LEFT, which eye will constrict with light shined in the RIGHT eye? What about left?
Afferent= CN II Efferent= CN III (PNS)
RIGHT eye only
What type of corticonuclear projections does the trigeminal nucleus generally receive? What is the exception?
Generally, CN V motor nucleus receives BILATERAL UMN projections
- EXCEPTION= lateral pterygoid m. that receives CONTRALATERAL UMN projections only
What is a presentation of a lesion to the trigeminal nucleus e.g. if there is a lesion to the midbrain, what will the presentation be?
Corticonuclear tracts to the RIGHT lateral pterygoid m. (muscle of mastication) come from the LEFT. The manifestation of a lesion is mandible deviation.
Thus, LEFT midbrain lesion= mandible deviation to the RIGHT (weak side)
What type of projections does the facial nucleus receive?
Upper Facial Nucleus= bilateral UMN
Lower Facial Nucleus= contralateral UMN ONLY
What type of projections does the nucleus ambiguus receive?
Primarily CONTRALATERAL projections
What muscle is controlled by the nucleus ambiguious? What structure does this muscle control? If there were a lesion in the LEFT midbrain, what would the expected presentation be?
- Musculous uvulae m. controls the uvula
- Receives CONTRALATERAL UMN projections
Thus, LEFT midbrain lesion will effect the RIGHT nucleus ambiguous. However, with a weak RIGHT musculous uvulae m. the uvula will deviate to the LEFT.
What type of projections does the hypoglossus nucleus receive? What is the exception? If there is a LEFT midbrain lesion, what would the expected presentation be?
Hypoglossal nucleus receives BILATERAL UMN projections
- EXCEPTION is genioglossus, which receives CONTRALATERAL UMN projections
Thus, LEFT midbrain lesion will effect the RIGHT hypoglossal nucleus; specifically, the genioglossus m. will be effect. Protrusion of the tongue will be to the RIGHT, the weak side.
Where do corticospinal tracts decussate?
Caudal medulla
Describe the presentation Medial Midbrain Syndrome (Weber) with a lesion to the LEFT rostral midbrain.
LEFT oculomotor palsy
RIGHT
- CN V= RIGHT deviation of jaw
- CN VII= RIGHT weakness of lower face
- CN X= uvula deviation to the LEFT
- CN XII= tongue protrusion to the RIGHT
- Corticospinal tracts= hemiparesis
Where is the lesion associated with Central Midbrain Syndrome (Claude Syndrome)?
Branches of the PCA & Superior Basilar Artery
What structures are effected in Central Midbrain Syndrome (Claude Syndrome)?
- CN III fasicules as they course ventrally (ipsilateral CN III palsy)
- Red Nucleus
- Cerebellothalamic fibers
Where is the CN III Palsy associated with Central Midbrain Syndrome?
IPSILATERAL
What is the function of the Red Nucleus?
Control of the distal muscles of the upper limb via RUBROSPINAL tract
**However, NOT clinically significant b/c of corticospinal tract (humans)
What structures are connected by the cerebellothalamic fibers? Where do cerebellothalamic fibers cross-over?
Cerebellothalamic fibers connect the cerebellum to the CONTRALATERAL thalamus
- After exiting the cerebellum, these fibers ascend the SCP
- SCP decussates in the caudal midbrain (Mickey Mouse)
What is the function of the cerebrothalamic fibers? What is the manifestation of a lesion to the cerebellothalamic fibers?
Cerebellothalmic fibers are sensory fibers sending information to the cortex; the cortex then sends impulses back down to the cerebellum to alter movement on the CONTRALATERAL side of the body
Thus, a lesion will cause ataxia and intention tremor on the CONTRALATERAL side of the body
Where Benedikt Syndrome the eponym for?
Medial + Central Midbrain Syndromes
Describe the presentation of Benedikt Syndrome.
BOTH= IPSILATERAL CN III Palsy
Medial=
- Contralateral mandible deviation
- Contralateral lower facial weakness
- IPSILATERAL uvula deviation (even though it effects the CONTRALATERAL nucleus ambiguous)
- Contralateral hemiparesis (corticospinal tracts)
Central=
- Contralateral ataxia & intention tremor
What is the additional manifestation of Benedikt Syndrome compared to just the medial & central midbrain syndromes alone??
SN lesion= CONTRALATERAL tremor/ involuntary movement at REST
What does MS have the most impact on?
Heavily myelinated tracts of the CNS
Describe the presentation a demyelination lesion to the caudal midbrain caused by MS. What structures will be effected? What will the presentation be?
Trochlear nucleus= paralysis of CONTRALATERAL superior oblique–>hypertropia (up & out)
Medial Longitudinal Fasiculus (MLF)= medial rectus= defect in conjugate horizontal movement with ADduction of IPSILATERAL eye
Cerebellothalamic fibers= CONTRALATERAL
- Intention tremor
- Dysmetria
- Dysdiadochokinesia (impaired RAM)
