Overview
The abducens nerve is cranial nerve six (CN VI) responsible for the motor innervation of the lateral rectus muscle.
Origin
Arises from the abducens nucleus in the dorsal pons of the brainstem, at the upper part of the rhomboid fossa, beneath the facial colliculus.
Segments & Course
Intraparenchymal segment
- From the abducens nucleus, fibres pass anteriorly through the pons medial to the facial nucleus to reach the pontomedullary junction
Cisternal segment
- It exits the brainstem from the inferior pontine sulcus, located at the pontomedullary junction, medial to the facial nerve and vestibulocochlear nerve.
- It courses between the anterior inferior cereballary artery (inferiorly) and the labyrinthine artery (superiorly to enter the prepontine cistern together with the basilar artery
- It ascends along the surface of the clivus enclosed within a fibrous sheath called the Dorello canal and pierces the dura inferior to the posterior clinoid process.
- It then courses over the medial petrous apex towards the cavernous sinus.
Cavernous segment
- Within the cavernous sinus, the abducens nerve is located inferolateral to the internal carotid artery, medial to the lateral wall of the sinus which contains:
- Oculomotor nerve
- Trochlear nerve
- Ophthalmic division of trigeminal nerve
- Maxillary division of trigeminal nerve
Intraorbital segment
- It enters the orbit through the superior orbital fissure within the Annulus of Zinn (common tendinous ring), below the inferior division of the oculomotor nerve and innervates the lateral rectus muscle.
Relations
It is the most inferior nerve passing through the tendinous ring, inferior to the inferior division of the oculomotor nerve.