The abducens nerve is the sixth cranial nerve (CN VI). It is a motor nerve responsible for abduction of the eye (TA: nervus abducens or nervus cranialis VI). It courses from the abducens nucleus, located in the dorsal pons, up to the cavernous sinus, via a long cisternal segment that is prone to injury, to its termination on the lateral rectus muscle.
It can be divided into five parts:
- nucleus and intraparenchymal portion
- cisternal portion
- Dorello canal portion
- cavernous sinus portion
- orbital portion
Gross anatomy
Nucleus and intraparenchymal portion
The abducens nucleus is a small nucleus situated at the upper part of the rhomboid fossa beneath the facial colliculus within the pons. Fibers pass anterior through the pons medial to the facial nucleus to reach the pontomedullary junction.
Cisternal portion
The abducens nerve is the most medial of the nerves, emerging immediately below the pons (facial nerve and vestibulocochlear nerve lateral to it) at the pontomedullary junction into the prepontine cistern. It is located within the anterior pontine arachnoid membrane and courses anterosuperiorly towards the petrous apex and cavernous sinus.
Dorello canal
The abducens nerve pierces the dura mater inferior to the posterior clinoid process, enclosed within a fibrous sheath called the Dorello canal, and courses over the medial petrous apex towards the cavernous sinus. Its oblique course and relatively anchored position in the Dorello canal make it prone to stretching when raised intracranial pressure from a space-occupying lesion causes transtentorial herniation (a sixth nerve palsy is the classic lateralizing sign of an extradural hematoma).
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, it supplies the lateral rectus. It is the most inferior nerve passing through the tendinous ring, inferior to the inferior division of the oculomotor nerve.
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