Third Cranial Nerve Lesions

oculomotor nerve
innervates: superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae, cillary muscle and iris sphincter

SYMPTOMS/SIGNS

“down and out” – because of antagonism of the trochlear nerve (superior oblique) and abducens nerve (lateral rectus)
ptosis – weakness of levator palpebrae
diplopia + strabismus – unable to maintain normal alignment when looking straight ahead
dilated, fixed pupil (anisocoria) + blurred vision – parasympathetic fibres originate from the Edinger-Westphal subnucleus of IIIrd nerve complex

ANATOMICAL BASIS (causes of IIIrd nerve dysfunction)

Nuclear Portion

column shaped
either side of the midbrain tegmentum
pathological causes: infarction, haemorrhage, neoplasm, abscess

Fascicular Midbrain Portion

courses ventrally
passes through the red nucleus
emerges from the medial aspect of the cerebral peduncle
pathological causes: infarction, haemorrhage, neoplasm, abscess

Fascicular Subarachnoid Portion

nerve runs in the subarachnoid space anterior to the midbrain and in close proximity to the posterior communicating artery
pathological causes: aneurysm, meningitis, meningeal infiltration, ophthalmoplegic migraine, compression from ipsilateral or mass effect (uncal herniation)

Fascicular Cavernous Sinus Portion

the nerve runs through the lateral wall of the cavernous sinus
it enters the sinus just above the petroclinoid ligament and inferior to the interclinoid ligament
pathological causes: tumour, pituitary apoplexy/infarction, vascular (giant intracavernous aneurysm, carotid artery-cavernous sinus fistula, cavernous sinus thrombosis), ischaemia, inflammatory (Tolosa-Hunt Syndrome)

Fascicular Orbital Portion

it enters the orbit through the superior orbital fissure
it then branches into superior and inferior divisions
superior -> levator palpebrae and superior rectus
inferior -> innervates the rest
axons are mostly uncrossed with 2 exceptions (axons to levator palpebrae are from both sides, those for superior rectus come from the contralateral side)
pathological causes: inflammatory (orbital inflammatory pseudotumour), endocrine (thyroid orbitopathy), tumour (haemangioma, lymphoma)

References and Links

Text books and Journal articles

LITFL

Social Media and Web Resources

Critical Care

Compendium

…more CCC

Chris Nickson

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

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