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Visual Neuroanatomy Efferent Pathways

Visual Neuroanatomy Efferent Pathways. Vivek Patel, MD University of Ottawa Eye Institute Neuro-Ophthalmology. Visual Neuroanatomy. Afferent – eye to brain Pupillary reflex arc Efferents – eye movements. Extra-Ocular Muscles. Infranuclear pathways. CN III.

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Visual Neuroanatomy Efferent Pathways

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  1. Visual NeuroanatomyEfferentPathways Vivek Patel, MD University of Ottawa Eye Institute Neuro-Ophthalmology

  2. Visual Neuroanatomy • Afferent – eye to brain • Pupillary reflex arc • Efferents – eye movements

  3. Extra-Ocular Muscles

  4. Infranuclear pathways

  5. CN III • Innervates Levator, inferior oblique & all recti except lateral rectus • Projects ventrally • Enters cavernous sinus after crossing PCOM

  6. Categorized by age Children Congenital AVM Tumor Young Adults Demyelination Vascular Tumor Older Adults Vascular Tumor CN III Injuries

  7. CN III Subnuclei • All subnuclei are ipsilateral EXCEPT • Levator subnucleus forms a fused central nucleus • Superior rectus subnuclei decussate to innervate contralateral superior rectus muscle

  8. IS it nuclear or peripheral ? It must be nuclear if • Bilateral CN III without ptosis • Unilateral CN III with bilateral ptosis BUT • Complete bilateral CN III • Bilateral ptosis May be either!

  9. CN IV • Nucleus just caudal and dorsal to III • Innervates Contralateral superior oblique • Exits brainstem dorsally • Longest intracranial course

  10. CN IV injuries • Intrinsic • Trauma • Tumor • Medulloblastoma • Ependymoma • Metastatic • Demyelination • Vascular • Congenital ( high vertical vergence amplitudes and objective excyclotorsion only) • Bilateral: V-pattern esotropia and excyclotorsion greater than 15 degrees. • Resultant compensatory head position?

  11. CN IV injuries • Extrinsic • Tumor • Pinealoma • Metastatic • Hydrocephalus / Aqueductal stenosis

  12. Skew Deviation? • Supranuclear cause of vertical misalignment • Does not necessarily obey the 3-step test • Ipsilateral intorsion (not extorsion as in IV palsy) • Interruption of otolith-ocular pathway at some point along it’s course

  13. Skew deviation - OTR • Vestibulo-cerebellar: • Ipsilateral head tilt • Ipsilateral hypotropia • Excyclo of hypo eye, incyclo of hyper eye • Midbrain: • Contralateral head tilt • Ipsilateral hypertropia • Excylo of hypo eye, incyclo of hyper eye

  14. Look for a lesion in: • cerebellum • Pons • midbrain

  15. Normal counter-roll R IV palsy Ocular tilt rxn (skew)

  16. CN VI • Innervates ipsilateral lateral rectus • Interneurons to contralateral medial rectus via MLF • Runs near: • CN VII • MLF and PPRF • Vestibular Nuclei • Peduncle

  17. CN VI • Origin: ponto-medullary junction • Projects ventrally along clivus • Tethered at apex of the petrous bone by petroclinoid ligament • Enters Cavernous sinus

  18. CN VI Injuries • Vascular • Anterior inferior cerebellar or paramedian perforators • Demyelination • Trauma • Tumor

  19. Cavernous Sinus • Site of multiple cranial nerve palsies • Vascular • Tumor • Idiopathic • Tolosa-Hunt

  20. Supranuclear control

  21. Internuclear Pathways • MLF • PPRF

  22. Paramedian Pontine Reticular Formation • Horizontal Gaze center • Initiates horizontal eye movements • Bilateral, within Pons • Projects to ipsilateral CN VI nucleus • Lesions of the PPRF cause ipsilateral gaze palsies • PPRF lesions do not affect oculocephalic & caloric reflexes

  23. MLF • Midbrain to cervical spine • Composed of interneurons – ipsilateral CN VI to contralateral CN III. • fascicle for horizontal gaze and vertical gaze that connects the VI and III nuclear complexes. • Trochlear nerve and otolith ocular pathways also use the MLF

  24. Vertical Gaze • Rostral Interstitial nucleus of the MLF (riMLF) (gaze initiation) • Interstitial Nucleus of Cajal (INC) (gaze holding) INC riMLF

  25. Upgaze • Lateral riMLF projects to contralateral inferior oblique and superior rectus sub-nuclei • Remember Superior Rectus fascicle decussates

  26. Downgaze • Medial riMLF projects downward to ipsilateral superior oblique and inferior rectus sub nuclei • Remember the CN IV fascicle decussates • Vertical gaze is initiated by Bilateral activation of the riMLF and INC.

  27. Alternating cover testing • Cover / uncover testing • Quantifying a deviation

  28. Name that lesion

  29. Benedikt’s • Involves Red Nucleus • Ipsilateral CN III • Contralateral involuntary movements

  30. Weber’s • Involves Cerebral peduncle • Ipsilateral CN III • Contralateral Hemiparesis

  31. PPRF lesion • Ipsilateral gaze palsy • Provides the supranuclear input to the abducens nuclear complex. • Isolated PPRF lesion will preserve the oculocephalic and caloric reflexes.

  32. PPRF & Nuclear sixth • Ipsilateral Gaze palsy with • Abnormal oculocephalic and caloric testing

  33. 1 and ½ syndrome • Lesion of PPRF, CN VI nucleus, MLF • Ipsilateral gaze palsy with • ipsilateral INO

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