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Abducens nerve (CN VI)

Dr Frank Gaillard et al.

The abducens nerve is the sixth cranial nerve. It is the "anticipation" in this infamous mnemonic. It's course from nucleus located in the dorsal pons, to its innervation of the lateral rectus can be divided into 4 parts:

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

Nucleus and intra-parenchymal portion

content pending

Cisternal portion

It is the most medial of the nerves emerging from immediately below the pons (facial nerve and vestibulocochlear nerve lateral to it). It courses superiorly with the anterior inferior cerebellar artery anterior to it, and the pons posterior, to pierce the dura over medial most aspect of the petrous ridge, passing through the inferior petrosal sinus in Dorello's canal. 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 (EDH).)

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 tendinous ring (see Figure 3) it supplies the lateral rectus.

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