Abducens Nerve (CN VI)

Abducens nerve (CN VI)

Concise emergency medicine guide to recognition, initial investigation and urgent management of sixth cranial nerve palsy, with emphasis on red flags that require urgent imaging and specialist referral.

Function and typical deficit

CN VI is a purely motor nerve supplying the lateral rectus. Lesion produces failure of abduction of the affected eye, resulting in an ipsilateral convergent (esotropic) resting position and horizontal binocular diplopia that is worse on gaze toward the affected side. Patients commonly adopt a head turn toward the paretic side to minimise diplopia.

Key anatomy and clinical implications

• The abducens nucleus lies in the dorsal pons and contains motor neurons to the ipsilateral lateral rectus plus internuclear connections (via the medial longitudinal fasciculus, MLF) that coordinate contralateral medial rectus activity. Nuclear (pontine) lesions therefore tend to cause conjugate horizontal gaze palsies rather than an isolated abduction deficit.
• The nerve exits the pons and traverses the subarachnoid space across the clivus, making it vulnerable to stretch with raised intracranial pressure and to traumatic stretch injuries.
• CN VI passes through the cavernous sinus adjacent to the internal carotid artery and enters the orbit via the superior orbital fissure. In the cavernous sinus it lies close to CN III, IV and the ophthalmic division of CN V (V1); processes here commonly produce multiple cranial nerve deficits....