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Abducens nerve

The abducens nerve is the sixth cranial nerve. Its course from nucleus located in the dorsal pons, to its innervation of the lateral rectus muscle can be divided into four parts:

  1. nucleus and intra-parenchymal portion
  2. cisternal portion
  3. cavernous sinus portion
  4. orbital portion

Nucleus and intra-parenchymal portion

Abducent nucleus is a small nucleus situated at the upper part of the rhomboid fossa beneath the colliculus facialis within the pons.

Cisternal portion

It is the most medial of the nerves emerging from immediately below the pons (facial nerve and vestibulocochlear nerve lateral to it) at the pontomedullary junction into the prepontine cistern. It courses anteriorly toward the clivus where it runs superiorly along the clivus enclosed within fibrous sheath called Dorello's canal and pierces the dura inferior to the posterior clinoid process. Then it courses over the medial petrous apex toward the cavernous sinus. It is its oblique course and relatively fixed anchor in Dorello's canal which makes it prone to stretching when raised ICP from a space occupying lesion causes transtentorial herniation (a sixth nerve palsy is the classic lateralising sign of an extradural haematoma).

Cavernous sinus portion

Within the cavernous sinus the abducens nerve is located inferolateral to the internal carotid artery medial to the lateral wall of the sinus.

Orbital portion

Having entered the orbit through the superior orbital fissure within the tendinous ring (see Figure 3) it supplies the lateral rectus.

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