Exam #3: Lesions II (Pons) Flashcards
How are brainstem lesions localized?
The level of the lesion is localized by the cranial nerve involved
Where are the nuclei for CN III located?
Rostral midbrain
Where are the nuclei for CN VI located?
Caudal pons
Where are the nuclei for CN XII?
Rostral Medualla
What structures will be effected by a lesion to the medial pons?
CN VI*
MLF
Corticospinal/ corticonuclear tracts
Medial lemniscus
What structures will be effected by a lesion to the medial medulla?
CN XII
Pyramids i.e. corticospinal tracts mostly
Medial lemniscus
When there are lesions to the medial brainstem, what is the general pattern of deficits i.e. what is the general pattern to the patient’s presentation?
- IPSILATERAL CN deficits
- CONTRALATERAL long tract signs
*****Note that this is referred to as an “alternating hemiplegia”
What is the clinical syndrome seen when there is a CN III lesion?
Upper alternating hemiplegia
What is the clinical syndrome seen when there is a CN VI lesion?
Middle alternating hemiplegia
What is the clinical syndrome seen when there is a CN XII lesion?
Lower alternating hemiplegia
What tracts are involved in lateral brain stem lesions?
Spinothalamic tract (CONTRALATERAL) Spinal tract of V (IPSILATERAL)
*****Note that both of these tracts are involved in pain & temperature sensation
What CN nuclei are involved in lateral brain stem lesions?
CN V CN VII CN VIII CN IX CN X
Where is the nucleus of CN V located in the brainstem?
Midpons
Where is the nucleus of CN VII located in the brainstem?
Caudal pons
Where is the nucleus of CN VIII located in the brainstem?
Caudal pons & medulla
Where is the nucleus of CN IX located in the brainstem?
Medulla
Where is the nucleus of CN X located in the brainstem?
Medulla
What causes a lesion to the medial rostral pons?
Lesion to the basilar artery, specifically the paramedian branches
What is the expected presentation of a lesion of the basilar artery affecting rostral pons i.e. the medial pontine basis?
*****Dysarthria Hemiparesis Syndrome
1) Corticospinal tract involved will give CONTRALATERAL UE & LE weakness
2) Corticonuclear tract involved will give CONTRALATERAL lower face weakness generally causing dysarthria. The specific muscles involved will be:
- Lateral pterygoid (mandible deviation away from the lesion)
- Musculus uvulae (uvula deviation toward the lesion)
- Genioglossus (tongue deviation away from the lesion)
What is the expected presentation of a lesion to the caudal pons i.e. the medial pontine basis? How would you differentiate this lesion from a lesion to the rostral pons?
*****Ataxic Hemiparesis Syndrome
1) Corticospinal tract involved will give CONTRALATERAL UE & LE weakness
2) Corticonuclear tract involved will give CONTRALATERAL lower face weakness & dysarthria
- Musculus uvulae (uvula deviation toward the lesion)
- Genioglossus (tongue deviation away from the lesion)
* Same as lesion to rostral pons, but the lateral pterygoid is NOT affected i.e. no mandible deviation
New aspect:
- Pontine nuclei/ Transverse pontine (pontocerebellar) fibers–> CONTRALATERAL ataxia
Neurologic examination reveals RIGHT upper & lower limb weakness accompanied by resistance to passive stretch (spasticity), exaggerated tendon reflexes ( hyperreflexia), and extensor plantar response (babinski sign). What tract is affected?
Corticospinal tract
Neurologic exam reveals a loss of 2-point discrimination, vibration, and limb position senses on the RIGHT side in the upper & lower limbs, trunk, and neck. What tract is affected? Where must the lesion be with the presentation described?
DC/ML & must be above the cervical level of the spinal cord
Neurologic exam reveals a loss of pin prick sensation to the right side of the face. What tract is affected?
LEFT trigeminalothalamic tract
A corneal reflex on the RIGHT eye could be elicited from either eye (not the left). What structure is affected?
Left CN VII
Recall,
- CN V= afferent
- CN VII= efferent
