nerve VI Palsy Sixth (VI) Nerve Palsy



• The abducens (VI) nerve (CN VI) innervates the ipsilateral lateral rectus (LR) muscle, abducting the eye. CN VI palsy is the most common isolated cranial nerve palsy. Patients present with binocular horizontal diplopia and esotropia. Children may not complain of diplopia.

• In adults aged over 50 years, CN VI palsies are most often due to microvascular ischemic peripheral nerve injury. In children, CN VI palsies are particularly alarming because of the frequent association with brain tumors.

• The CN VI nucleus is located in the dorsal lower pons. The nuclear complex contains motor neurons to the ipsilateral lateral rectus (LR) muscle and interneurons that project, by the medial longitudinal fasciculus (MLF), to the medial rectus (MR) subnucleus of the contralateral CN III nuclear complex. Therefore, a nuclear lesion will produce an ipsilateral gaze palsy and not a CN VI palsy. The fascicles exit at the pontomedullary junction and the nerve runs along the clivus and travels over the petrous apex of the temporal bone, where it is tethered at the petroclinoid ligament in Dorello’s canal. The nerve courses within the cavernous sinus lateral to the internal carotid artery and enters the orbit through the superior orbital fissure.


• CN VI palsy can occur in all ages; etiology varies depending on age group

• No racial or sex predilection


• 11 per 100,000

• Peak incidence in seventh decade


• Diabetes

– Only independent risk factor linked to ischemic palsies

• Hypertension

• Hyperlipidemia

• Obesity

• Trauma

• Alcohol abuse

– Wernicke-Korsakoff syndrome is the best known neurologic complication of thiamine (vitamin B1) deficiency.


• Nucleus:

– A CN VI palsy does not occur with nuclear lesions.

• Fascicle in pons:

– Demyelinating

– Infarction

– Neoplasm

• Nerve root in cerebellopontine angle:

– Neoplasm (acoustic neuroma)

• Subarachnoid space:

– Aneurysm

– Meningitis

– Inflammation

– Infection

– Neoplasm

• Petrous ridge:

– Recurrent otitis media

– Nasopharyngeal carcinoma

– Chondrosarcoma

• Cavernous sinus:

– Cavernous sinus fistula, thrombosis

– Neoplasm

– Internal carotid artery aneurysm, dissection

• Orbital apex:

– Optic neuropathy

• Orbit:

– Neoplasm

– Inflammation

– Infection


• Ischemic

– Diabetes

– Hypertension

questionable independent risk factor

• Compressive

• Inflammatory

• Traumatic

– Unilateral or bilateral

• Intracranial hypertension

– Unilateral or bilateral

• Intracranial hypotension

– Post dural puncture, CSF leak

• Multiple sclerosis

Pediatric Considerations

• Congenital

– Isolated congenital absence of abduction extremely rare

– Transient CN VI palsy may occur due to birth trauma.

Möbius syndrome

– Facial diplegia associated with horizontal gaze abnormalities

– Etiologies include maldevelopment and intrauterine insults.

– Duane’s retraction syndrome

Unilateral or bilateral abduction deficits, variable adduction abnormalities, palpebral fissure narrowing and globe retraction on attempted adduction

Congenital absence of 6N neurons with aberrant innervation of LR by branches of CN III

• Most common causes of CN VI palsies in children are tumors (45%), trauma, increased intracranial pressure (ICP).

– May be post-viral when isolated


• Nucleus:

– Conjugate horizontal gaze palsy

• Fascicle in pons:

– Ipsilateral CN V palsy

– Ipsilateral CN VII palsy

– Ipsilateral Horner’s syndrome

– Contralateral hemiparesis (Raymond’s syndrome)

• Nerve root in cerebellopontine angle:

– Ipsilateral deafness or tinnitus

• Petrous ridge:

– Severe facial and eye pain (Gradenigo’s syndrome)

– Occasionally facial paralysis

• Cavernous sinus:

– CN III, IV, or V palsy

– Ipsilateral Horner’s syndrome

• Orbital apex:

– Optic neuropathy

• Orbit:

– Proptosis

– Chemosis

– Lid swelling



• Abrupt onset when microvascular ischemic

• Purely horizontal diplopia

– Binocular

– Worse at distance

– Worse in direction of action of the paretic LR

• Inquire about headache, pain, hearing loss, trauma, symptoms of giant cell arteritis (GCA)


• Patients may present with a head turn.

• Ipsilateral abduction deficit

• Incomitant esotropia, worse in direction of weak LR

• Exophthalmometry and orbit examination

• Forced duction test

• Assess orbicularis oculi strength to look for myasthenia gravis (MG)


• Critical to evaluate function of other cranial nerves

• Look for papilledema

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Nov 9, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on nerve VI Palsy Sixth (VI) Nerve Palsy

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