The problem with parasites

There are many things that you don't want to get in your brain: annoying pop songs, advertising jingles, unfortunate images. All of these pale in comparison to a hydatid cyst. The cyst is a larval stage of a tapeworm called Echinococcus granulosus, which is a parasite found in canines. These organisms are present in the feces of infected dogs, and are transferred, thankfully rarely, to humans through ingestion. It is therefore more common in countries where dogs are used to herd livestock. Once the cyst is inside the gut it can sometimes break into the bloodstream. From there the most common route is directly to the liver. A person can survive with several small hydatid cysts in their liver and suffer no ill effects. Sometimes, however, the cysts can wend its merry way to other parts of the body including the brain, where it can grow to the size of a golf ball.
By now you probably have a picture in your mind of what this cyst might look like. You're probably wrong. Happily though, I have found a video of a hydatid cyst being removed successfully from some poor guy's brain. It is not for the faint hearted, but it is morbidly fascinating.