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Trochlear nerve


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Published in: Health & Medicine

Trochlear nerve

  1. 1. Trochlear Nerve Dr Hytham Nafady
  2. 2. Introduction <ul><li>Trochlear nerve has only somatic motor component. </li></ul>Somatic motor innervates the superior oblique muscle of the contralateral orbit. Somatic motor (general somatic efferent)
  3. 3. Anatomy <ul><li>Nucleus. </li></ul><ul><li>Intracranial course </li></ul><ul><li>Extracranial course </li></ul>
  4. 4. Segments of the trochlear nerve <ul><li>Central, </li></ul><ul><li>Cisternal, </li></ul><ul><li>Cavernous, & </li></ul><ul><li>Orbital </li></ul>
  5. 5. Trochlear nucleus <ul><li>Trochlear nucleus is located in tegmentum of midbrain, at the level of inferior colliculus. </li></ul><ul><li>It is located ventral to the periaqueductal grey matter, inferior to the oculomotor nucleus & superior to the medial longitudinal bundle. </li></ul>
  6. 7. Trochlear nucleus .
  7. 8. * = 4 th cranial nerve nucleus
  8. 9. Superior medullary vellum
  9. 10. Central segment <ul><li>Course posteriorly & caudally surrounding the aqueduct of sylvius. </li></ul><ul><li>Nerves decussate at anterior medullary velum in the roof of aqueduct before exiting from dorsal aspect of midbrain below the inferior colliculus. </li></ul>4
  10. 11. Cisternal segment <ul><li>Course through the ambient cistern between the posterior cerebral & superior cerebellar arteries. </li></ul>
  11. 13. PcoA Cn IV C n III
  12. 14. Cavernous segment <ul><li>The trochlear nerve enters the cavernous sinus superior to the petroclinoid ligament. </li></ul><ul><li>The cavernous segment of the trochlear nerve course through the lateral wall of the cavernous sinus below the oculomotor nerve. </li></ul>
  13. 16. Cn 4 Cn 5 O Cn 6 Cn 3 Cn 5 mx
  14. 17. Orbital segment <ul><li>The trochlear nerve enters the orbit through the superior orbital fissure outside the annular ring of Zinn. </li></ul><ul><li>The orbital segment of the trochlear nerve crosses medially over levator palpebrae superioris and superior rectus muscles before entering the belly of superior oblique muscle </li></ul>
  15. 18. Superior orbital fissure & annular ring of Zinn
  16. 19. Cn 3 i Cn 3 s Cn 6 Cn 4
  17. 20. Superior oblique muscle <ul><li>Superior oblique muscle originates from orbital apex, above annulus, and runs along superonasal aspect of orbit before becoming a tendonous cord. Tendon passes through trochlea and abruptly turns laterally and posteriorly to insert on the globe. Tendon is cordlike as it passes beneath nasal border of superior rectus but fans out to form a broad insertion. </li></ul>
  18. 22. Trochlear nerve palsy <ul><li>Nucleus. </li></ul><ul><li>Central segment. </li></ul><ul><li>Cisternal segment. </li></ul><ul><li>Cavernous segment. </li></ul><ul><li>Orbital segment. </li></ul>
  19. 24. Nucleus & central segment
  20. 25. Left superior oblique palsy & right internuclear ophthalmoplegia
  21. 26. Cisternal segment <ul><li>Trochlear nerve neuroma. </li></ul><ul><li>Vascular loop compression </li></ul>
  22. 27. Trochlear nerve schwannoma
  23. 28. Trochlear nerve schwannoma along cisternal & cavernous segments
  24. 29. Vascular loop compression of the trochlear nerve by anomalous left PCA
  25. 30. Bilateral trochlear nerve palsies following dorsal midbrain haemorrhage
  26. 31. Isolated trochlear nerve palsy with dorsal midbrain hemorrhage
  27. 32. Atrophy of the superior rectus muscle in trochlear nerve palsy
  28. 33. Superior oblique muscle atrophy
  29. 34. Trochlear nerve palsy <ul><li>Diplopia on going downstairs. </li></ul>
  30. 35. Trochlear nerve palsy <ul><li>Congenital right trochlear nerve palsy with compensatory left head tilt. </li></ul>
  31. 36. <ul><li>Post-traumatic bilateral trochlear nerve palsy with: </li></ul><ul><li>right hypertropia on right head tilt & </li></ul><ul><li>left hypertropia on left head tilt. </li></ul>