An overview of the third, fourth and sixth cranial nerve palsies Palsies of the third, fourth and sixth cranial nerves have ophthalmological consequences. W Marais, MB ChB, MMed (Ophth); S Barrett, MB ChB, MMed (Ophth) Consultants, Department of Ophthalmology, University of the Free State, Bloemfontein, South Africa Correspondence to: W Marais ([email protected]) Third nerve (oculomotor • nuclear third nerve palsy will spare the Basilar part of CN III[2] nerve) ipsilateral, and aect the contralateral, e basilar part of CN III Cranial nerve III (CN III) innervates the superior rectus. • starts as a series of ‘rootlets’ superior, inferior, medial recti and the • Medial rectus, inferior rectus and • leaves the midbrain on the medial aspect inferior oblique muscles. It also innervates inferior oblique subnuclei of the cerebral peduncle, before coalescing the levator palpebrae superioris and carries • paired to form the main trunk with it the parasympathetic innervations • innervate their corresponding ipsi- • then passes between the posterior to the pupil. Involvement of CN III will lateral muscles cerebral and superior cerebellar arteries produce a symptom complex that involves • lesions conned to the nuclear com- • runs lateral to and parallel with the one or several of these muscles and usually plex are relatively uncommon posterior communicating artery results in double vision.[1] • most frequent cause of palsy are vascular • is unaccompanied by other cranial disease, primary tumours and metastases nerves, therefore isolated CN III is Components of CN III • involvement of the paired medial commonly basilar (Fig. 1). • nuclear complex rectus subnuclei causes a wall-eyed • fasciculus bilateral internuclear ophthalmoplegia Important causes of basilar CN III • basilar (WEBINO), characterised by exo- palsy • intracavernous tropia, and defective convergence Aneurysm • intraorbital and adduction. Lesions involving the Aneurysm of the posterior communicating • pupillomotor bres. entire nucleus are oen associated with artery at its junction with the internal involvement of the adjacent and caudal carotid artery typically presents as acute, Nuclear complex[2] fourth nerve nucleus. painful third nerve palsy with pupil • situated in the midbrain • Fasciculus[2] involvement. • at the level of the superior colliculus • consists of eerent bres which pass • ventral to the Sylvian aqueduct. from the third nerve nucleus through Head trauma the red nucleus and the medial aspect Head trauma resulting in extradural/ e nuclear complex is composed of the of the cerebral peduncle subdural haematoma (Fig. 2) causes a following paired and unpaired subnuclei:[2] • emerges from the midbrain and passes tentorial pressure cone with downward • Levator subnucleus into the interpeduncular space herniation of the temporal lobe and • unpaired caudal midline structure • causes of nuclear and fascicular lesions compresses the CN III as it passes over the • innervates both levator muscles are similar, except that demyelination tentorial edge, initially causing irritative • lesions conned in this area will may aect the fasciculus.[2] miosis followed by mydriasis and total CN therefore give rise to bilateral ptosis. III palsy. • Superior rectus subnuclei Midbrain fascicular third cranial • paired nerve palsies Intracavernous part of CN III[2] • innervates the respective contralateral Table 1 describes midbrain fascicular third e intracavernous part of CN III enters superior rectus cranial nerve palsies.[1,2] the cavernous sinus by piercing the dura Table 1. Midbrain fascicular third cranial nerve palsies Syndrome Signs/characteristics Location of lesion Benedikt Ipsilateral CN III palsy Red nucleus Contralateral extrapyramidal signs Hemitremor/involuntary movements Nothnagel Ipsilateral CN III palsy Fasciculus Cerebellar ataxia Superior cerebellar peduncle Claude Combination of Benedikt and Nothnagel syndromes Weber Ipsilateral CN III palsy Cerebral peduncle Contralateral hemiparesis 147 CME April 2013 Vol. 31 No. 4 Cranial nerve palsies lateral to the posterior clinoid process Intracavernous CN III palsy is usually onset of diplopia as an aneurysm expands. (Fig. 3). Within the cavernous sinus the associated with Pupillary involvement may be the only sign CN III runs in the lateral wall above CN • CN IV of CN III palsy. IV. Anteriorly in the cavernous sinus it • CN VI divides into superior and inferior branches, • rst division of CN V. Signs of right CN III palsy[2] entering the orbit through the superior • weakness of the levator with ptosis orbital ssure within the annulus of Zinn. The intra-orbital part of CN III[2] • eye abducted in primary position due to e superior division innervates the unopposed action of the lateral rectus Important causes of intracavernous CN • levator muscle III palsy • superior rectus. • normal abduction • Diabetes – causes a vascular palsy usually • intorsion of the eye which increases sparing the pupil. e inferior division innervates the on down gaze due to intact function of • Pituitary apoplexy (haemorrhagic in- • medial rectus superior oblique muscle farction) may cause a CN III palsy if the • inferior rectus – the branch to the inferior • limited adduction due to weakness of gland swells laterally and impinges on oblique also contains parasympathetic medial rectus muscle the cavernous sinus. preganglionic bres from the Edinge- • limited supraduction due to weakness • Intracavernous pathology such as Westphal subnucleus of superior rectus and inferior oblique • aneurysm • sphincter pupillae. muscles • meningioma • limited infraduction due to weakness of • carotid-cavernous stula Lesions to the inferior division are inferior rectus muscle • granulomatous inammation (Tolosa- characterised by • dilated pupil with defective accom- Hunt syndrome). • limited abduction modation due to parasympathetic palsy. • limited infraduction • dilated pupil. Aberrant regeneration[1,2] • may follow acute traumatic and Superior and inferior palsies are commonly compressive (but not vascular) third traumatic or vascular. nerve palsies • the endoneural nerve sheaths remain Pupillomotor fibres[2] intact in vascular pathology, may be These fibres are located superficially in the breached in traumatic and compressive superomedial part of CN III. Their blood lesions supply comes from the pial blood vessels. • bizarre defects in ocular motility Fig. 1. Dorsal view of the course of the third The main trunk of CN III is supplied by • elevation of the upper eyelid on nerve. the vasa nervorum. Involvement of the attempted abduction or infraduction pupil is of great importance because it • caused by misdirection of regenerating differentiates a ‘surgical’ from a ‘medical’ axons which reinervate the wrong lesion. extraocular muscle • pupil may also be involved. Surgical CN III lesions[2] Causes include Causes of isolated CN III palsy[2,3] • trauma 1. Idiopathic – 25 % • aneurysms 2. Vascular disease • uncal herniation. • diabetes • hypertension ese lesions characteristically involve the • most common cause of pupil-sparing Fig. 2. Mechanism of third nerve palsy by pupil by compressing the pial blood vessels CN III extradural haematoma. and the supercially located pupillary • spontaneous recovery in 3 months bres. • diabetic CN III palsy may be associated with periorbital pain Medical CN III lesions[2] • occasionally the presenting feature of • causes include hypertension and diabetes diabetes • characteristically spare the pupil • pain is therefore not helpful in • the microangiopathy involves the vasa dierentiating aneurismal and diabetic nervorum, causing ischaemia of the main CN III nerve palsy trunk. 3. Aneurysm • the posterior communicating artery at its Fig. 3. Location of cranial nerves in the ese principles are not infallible. Pupillary junction with the internal carotid artery cavernous sinus viewed from behind. involvement may develop a few days aer • pupil involvement 148 CME April 2013 Vol. 31 No. 4 Cranial nerve palsies 4. Trauma Fourth nerve (trochlear nerve) superior orbital ssure above and lateral • direct and secondary to subdural Anatomy of CN IV[2,3] to the annulus of Zinn. haematoma with uncal herniation Important features of CN IV • trivial head trauma not associated with • only cranial nerve to emerge from the Intraorbital part of CN IV loss of consciousness should alert one dorsal aspect of the brain (Fig. 4) • innervates the superior oblique. of a basal intracranial tumour causing • crossed cranial nerve – it means the nerve trunk to be stretched and that nerve nucleus innervates the Symptoms and signs of CN IV tethered contralateral superior oblique muscles palsy[5] 5. Miscellaneous (uncommon) • very long and slender nerve. A fourth nerve palsy typically causes • tumours diplopia that is worse in down gaze. Hence, • syphillis Components of CN IV patients almost always report diplopia (or • meningeal inammation • nucleus tendency to close one eye) while reading. • giant cell arteritis • fasciculus • vasculitis associated with collagen • trunk Signs of CN IV palsy[2] vascular disorders • intracavernous • acute onset of vertical diplopia in the • ophthalmoplegic migraine • intraorbital. absence of ptosis • internal carotid artery dissection • characterised by a head posture • myasthenia may also mimic intermittent Nucleus • features of nuclear, fascicular and pupil-sparing CN III palsy • located at level of the inferior colliculus peripheral CN IV are clinically identical • chemotherapeutic toxicity. ventral to the Sylvian aqueduct •