There might not be a more horrifying good-news, bad-news scenario than this recent report from doctors in Spain. They originally believed their patient had brain cancer, only to later discover he actually had worms inside his head. The doctors detailed their macabre case over the weekend in the journal Emerging Infectious Diseases. The 60-year-old man had developed brain lesions that initially resembled metastatic cancer on an imaging scan but, upon closer examination, were found to be cysts belonging to the pork tapeworm (Taenia solium). Thankfully, the man responded well to antiparasitic treatment. “Our study highlights cryptic local Taenia solium nematode transmission risks and diagnostic challenges in nonendemic regions,” the doctors wrote. The brain worm T. solium can sicken people in two ways, depending on how we catch it. If we eat the undercooked meat of pigs or other host animals infected with larval cysts, the cysts will reach our gut and mature into adult worms, causing the stereotypical gastrointestinal illness associated with tapeworms. These worms will eventually mate and lay eggs that come out in our poop. Normally, these eggs are supposed to end up in vegetation that’s consumed by pigs, starting the cycle again, but if the eggs infect another person, they only ever reach their cyst stage of life.