Abducent nerve


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Abducent nerve

  1. 1. Introduction • Abducens nerve has only a somatic motor component (general somatic efferent) that supplies lateral rectus muscle.
  2. 2. Abducens nerve anatomy
  3. 3. Origin • Abducens nucleus originates from the tegmenum pontis at the level of facial colliculus. • The nucleus is located; 1. anterior to the 4th ventricle, 2. posterior to the medial leminiscus, 3. Lateral to the medial longitudinal fasciculus, & 4. Medial to facial nerve & trigeminal spinal nucleus. • The facial colliculus is a focal bulge in the floor of the fourth ventricle formed by looping fibers of the facial nerve around the abducens nucleus.
  4. 4. Abducent nucleus .
  5. 5. The abducens nucleus contains 3 types of neurons: 1. Abducens motor neurons which innervate the ipsilateral lateral rectus muscle. 2. Abducens internuclear neurons, which project to the contralateral medial rectus subnucleus of the oculomotor nucleus via the medial longitudinal fasciculus. 3. Neurons that project to the cerebellar flocculus
  6. 6. Central course • The abducens nerve fascicle course antero-inferiorly through the pontine tegmentum adjacent to the facial nerve and exit from the brain stem at the ponto- medullary sulcus.
  7. 7. Intracranial course Dorello's canal is an osteofibrous conduit located at the level of the petrous apex through which the abducens nerve courses to reach the cavity of the cavernous sinus • Cisternal segment • Petro-clival segment • Cavernous segment • Orbital segment
  8. 8. Cisternal segement • courses superiorly through the prepontine cistern, to pierce the dura over medial most aspect of the petrous ridge.
  9. 9. Petroclival segment Cavernous segment Petroclival segment Cisternal segment MC
  10. 10. Petroclival segment Dorello's canal is an osteofibrous conduit located at the level of the petrous apex through which the abducens nerve courses to reach the cavity of the cavernous sinus
  11. 11. Cavernous segment The cavernous segment of the abducens nerve lie within the body of the sinus unlike the oculomotor , trochlear & V1 & V2 divisions of the trigeminal nerve which lie within the lateral wall of the sinus.
  12. 12. Cn IV CN V1 Cn VI Cn III Cn V2
  13. 13. Orbital segment • The abducens nerve enters the orbit through the superior orbital fissure and passes through the annular ring of Zinn.
  14. 14. Superior orbital fissure & annular ring of Zinn
  15. 15. Abucens nerve pathology • Nucleus & central segment • Cisternal segment • Petrous segment • Cavernous segment • Orbital segment
  16. 16. Aplasia or hypoplasia of the abducens nerve • Duane syndrome. • Mobius syndrome. • HGPPS (Horizontal Gaze Palsy with Progressive Scoliosis).
  17. 17. Duane syndrome
  18. 18. Mobius syndrome It is a congenital disorder characterized by • Bilateral facial diplegia • Convergent squint Secondary to 6th & 7th cranial nerve palsies Associations: Other cranial nerve plasies: 5th , 9th , 10th & 12th cranial nerves. Craniofacial abnormalites. Chest wall abnormalities. Upper & lower limb abnormalities.
  19. 19. Normal subject Mobius syndrome
  20. 20. Nucleus • Pontine hemorrhage. • MS • glioma
  21. 21. Pontine hemorrhage
  22. 22. MS
  23. 23. Central segment • The same as nuclear pathology.
  24. 24. Pontine hemorrhage
  25. 25. Cisternal segment • Duplicted abucens nerve (normal variant)
  26. 26. Duplicated abducens nerve with normal abduction
  27. 27. Diabetic or viral neuropathy Post-contrast
  28. 28. Post-contrast
  29. 29. Petroclival segment pathology • Petroclival meningioma. • Skull base destructive lesion. • Neuroma. • Usher syndrome.
  30. 30. Usher syndrome • Dilatation of the subarachnoid spaces surrounding the cranial nerves with petrous apex cephaloceles in Usher syndrome. • Usher syndrome is an autosomal recessive disorder characterized by retinitis pigmentosa & congenital SNHL.
  31. 31. Petroclival meningioma
  32. 32. Ganglio-neurofibroma
  33. 33. One & half syndrome • Complete horizontal gaze palsy, when looking toward the side of the lesion. • Half gaze palsy, when looking toward the opposite side.
  34. 34. One & half syndrome
  35. 35. Lateral rectus muscle atrophy
  36. 36. Lateral rectus muscle atrophy 1 year after post-traumatic 6th Cn palsy