Abducens nerve (CN VI)
Nerve · CN VI Motor
From the abducens nucleus in the lower pons it leaves at the pontomedullary junction, climbs the clivus in the subarachnoid space, bends sharply over the petrous apex under the petroclinoid ligament (Dorello's canal) and runs free inside the cavernous sinus beside the internal carotid artery before entering the orbit through the superior orbital fissure within the tendinous ring. Motor to lateral rectus only.
Traced from the start
- Pons
- Abducens nerve (CN VI)
Detail
- Motor
- Lateral rectus (abduction)
- Nucleus
- Pons, beneath the facial colliculus; also houses interneurones to the contralateral medial rectus for conjugate gaze
- Vulnerability
- Longest subarachnoid course of any cranial nerve and tethered at the petrous apex, so it is stretched by any rise in intracranial pressure or downward brain shift
When it goes wrong
Raised intracranial pressure from any cause (tumour, idiopathic intracranial hypertension, hydrocephalus) stretching the nerve over the petrous ridge
Unilateral or bilateral sixth nerve palsy as a false localising sign: horizontal diplopia worse on looking towards the affected side, with failure of abduction
Microvascular mononeuropathy in diabetes or hypertension
Isolated painless sixth nerve palsy that recovers over weeks to months
Cavernous sinus thrombosis spreading from a mid-facial or sphenoid sinus infection, or a carotid–cavernous fistula
Sixth nerve palsy is usually the first cranial nerve sign because VI runs free within the sinus while III, IV, V1 and V2 lie protected in the lateral wall
Petrous apicitis complicating otitis media (Gradenigo syndrome)
Sixth nerve palsy with retro-orbital pain (V1) and persistent ear discharge
Practise this structure
1 question in the bank tagged Extraocular Muscles.