MRA or CTA, That's the Question

A 26-year-old woman developed a painful left pupil-involving oculomotor palsy. Magnetic resonance imaging of the brain and orbits with and without fat suppression and gadolinium and magnetic resonance angiography of the head were normal. A computed tomographic angiogram showed a left 7-mm posterior communicating artery aneurysm. The different neuroimaging modalities used to diagnose intracranial aneurysms are discussed.