Most cases of this are discovered in infants and children with stridor and swallowing difficulties. But this MRI is of a woman in her forties with headache. You notice her gait is somewhat clumsy, there is diminished upward gaze, truncal instability, and bilateral increased reflexes.
Challenge: What's the diagnosis?
This image and case are from a www.urmc.rochester.edu website, shown under Fair Use. This is because I couldn't find a great UpToDate article.