Aetiology and Affected Areas in brain stem syndromes, including saccades and smooth pursuit. Conditions include fovilles syndrome, webers, encephalopathy and more.
- **Vascular causes**: Infarcts due to occlusion of small penetrating arteries (e.g., lateral medullary syndrome, also called Wallen...
Brainstem syndromes
Important definitions
Pyramidal tract:
• Fibres originate in the cerebral cortex, carrying upper motor nerve fibres to the spinal cord
(corticospinal) and brainstem (corticobulbar).
• Transmit signals for the voluntary control of the musculature of the body and face.
Cerebral peduncles:
• Two stalks which attach the cerebrum to the brainstem
• Located in the anterior part of the midbrain
• Contain the ascending and descending nerve fibres between the brain and the brainstem
Red nucleus:
• Lies within the midbrain
• The red nucleus is pale pink which is believed to be due to the presence of iron
• Receives inputs from the cerebellum of the opposite side the motor cortex of the same side
• Motor control so tremors can occur when affected
Brainstem lesions
• Nuclear- they are rare
• Internuclear- microvascular
• Infranuclear (below the level of nuclei)- e.g stroke
Oculomotor nerve (CN III)
• Origin – midbrain at level of superior colliculus
• Exits – through superior orbital fissure
• Two nuclei
o Oculomotor nerve nucleus - SR, IR, MR, IO and levator palpebrae superioris
o Edinger-Wesphal nucleus (accessory) - sphincter pupillae and ciliary body
(parasympathetic)
• Two types of efferent nerve fibres
o Somatic (EOMs) and visceral (sphincter and ciliary body)
• All the muscles are innervated by corresponding sub-nucleus
• All sub-nuclei innervate ipsilateral muscles, except two
o SR sub-nucleus
o Central caudal nucleus (CCN)- which innervates bilateral levators
• Hence a bilateral 3rd is likely a nuclear lesion
, Nuclear lesions of 3rd CN- Commonly due to infarction, demyelination and/or metastatic
tumour.
• Central caudal nucleus (CCN) supplies both levator muscles so lesion results in bilateral
ptosis
• with / without unilateral SR limitation
• If bilateral limitation of elevation Lesion affecting SR subnucleus
• Unilateral III with contralateral superior rectus palsy and bilateral ptosis
• Bilateral III with spared levator function Bilateral total III
Bilateral ptosis
Bilateral medial rectus palsy
• Isolated medial rectus, inferior oblique and inferior rectus palsy
Fascicular lesions of 3rd CN- Commonly due to infarction, demyelination and/or metastatic
tumour.
“Fascicular - nerve affected after leaving nucleus but not yet at brainstem”
• If unilateral limitation of elevation - Not SR subnucleus
• Involvement of SR nerve fascicles (axons after leaving nucleus)
• Axons from 1 SR subnucleus cross and pass through contralateral, as well as ipsilateral,
subnucleus
Symptoms of syndromes:
• III nerve palsy and contralateral hemiplegia with involvement of corticospinal tracts
• III nerve palsy with contralateral ataxia and intention tremor with involvement of red
nucleus.
e.g
Nothnagels syndrome: Lesion in the superior cerebellar peduncle producing an ipsilateral III nerve
palsy and cerebellar ataxia.
Benedikts syndrome: Lesion in the region of the red nucleus resulting to an ipsilateral III nerve palsy
and contralateral hemitremor.
Werber’s syndrome: Lesion in the area of cerebral peduncle, resulting in ipsilateral III nerve palsy
and contralateral hemiparesis.
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