Anyone remember this episode of Grey's Anatomy?

The patient had some sort of parasite or something in his/her brain. The website for the show does have an explanation for every episode, but it will take forever to go through it all, each description starts with a partial description of the episode and then you need to expand it to see the rest, and I just have no idea how long ago it played? Which season it was? I was hoping someone had a rough idea of what else was on that episode and the season.

Thanks.