Neuroscience · Year 2 · from Neuroscience
Case 2: Third Nerve Palsy from Posterior Communicating Artery Aneurysm
Patient Presentation
Demographics: 52-year-old female
Chief Complaint: Double vision and droopy right eyelid for 2 days, with new headache
History of Present Illness: Two days ago, the patient noticed her right eyelid was drooping and she began seeing double. The double vision is horizontal and worsens when she tries to look to the left. She also developed a new headache, dull and constant, located behind her right eye. The headache is moderate in severity and not the worst headache of her life. She has a history of hypertension. Her mother had a "brain hemorrhage" at age 58.
Physical Examination:
- Vital signs: BP 162/94, HR 76, T 37.0C
- General: Uncomfortable appearing, holding right eye closed to avoid diplopia
- Neurological:
- Mental status: Alert and oriented; appropriate
- Cranial nerves:
- II: Visual acuity normal; visual fields full
- III (Right): Complete ptosis; when lid lifted manually: pupil 6 mm and unreactive to light (direct or consensual); eye is deviated "down and out" (lateral and inferior); cannot adduct, elevate, or depress the eye (medial rectus, superior rectus, inferior rectus, inferior oblique all weak)
- III (Left): Normal
- IV: Right superior oblique intact (eye intorts when attempting to look down and in)
- VI: Right lateral rectus intact (can abduct)
- V, VII, VIII, IX, X, XI, XII: Normal
- Motor: 5/5 throughout
- Neck: Supple
Workup:
- CT head without contrast: No hemorrhage
- CT angiography: 7 mm saccular aneurysm arising from the junction of the right internal carotid artery and posterior communicating artery, projecting inferolaterally
- MRI brain: Aneurysm confirmed; no recent infarction
Diagnosis: Right third cranial nerve palsy secondary to unruptured right posterior communicating artery aneurysm
Treatment:
- Emergent neurosurgical and neurointerventional consultation
- Blood pressure control (goal SBP <140)
- Endovascular coiling of aneurysm performed on hospital day 1
- Aspirin 81 mg initiated post-procedure
Clinical Course: The patient tolerated aneurysm coiling without complication. Her headache improved within 24 hours. The ptosis and pupillary dilation persisted at discharge. At 3-month follow-up, ptosis had partially improved, and the pupil had regained some reactivity (though still larger than left). At 6 months, she had near-complete recovery of eye movements with only mild residual ptosis.
Clinical Pearl: An acute, painful third nerve palsy with pupil involvement is an aneurysm until proven otherwise. The posterior communicating artery aneurysm compresses the third nerve as it courses between the PCA and superior cerebellar artery. The pupil-involving pattern (mydriasis) occurs because parasympathetic fibers traveling on the outside of the nerve are compressed first. This "surgical" third nerve palsy contrasts with "medical" third nerve palsies from diabetes or vasculopathic disease, which typically spare the pupil (due to ischemia affecting the center of the nerve but sparing peripheral parasympathetic fibers).