Case Study 195: Brain Aneurysm - PCOM A posterior communicating artery (PCOM) aneurysm is one of the most common causes of a cranial nerve III palsy - that’s the nerve that moves most of the eye muscles, controls the eyelid, and constricts the pupil. When compressed by an aneurysm, patients can present with: 👁 Droopy eyelid (ptosis) 👁 Eye deviation “down and out” 👁 Dilated pupil - this is a key red flag! 💡 Did you know? 🔹 About 2-5% of the population have a brain aneurysm, but most never ru