Hydatid Disease (Part IV)
The larval form of E. granulosus manifests itself as a cyst, called a hydatid cyst. The cyst is actually not a single larva, but a fluid filled balloon of tissue filled with large numbers of tiny larval forms, called protoscolices (sing. protoscolex). Each protoscolex has the potential, if ingested by a dog, of becoming an adult tapeworm in the intestines of a dog, where the cycle can start again. Note that dogs carry these worms without problems or symptoms. You cannot tell by looking at a dog if he is infested with E. granulosus.
Here are two pictures of livers with hydatid cysts. The first shows one during a surgery to remove the cysts.
The second shows a dissected specimen from a liver lobe that had to be removed.
The lungs are the next most frequent site, but any organ can be targeted. Here is a hydatid cyst of the of brain being removed by a surgeon.
And here is a schematic of the anatomy of the cyst itself. The protoscolices are microscopic, but the cysts themselves can grow to be 14 inches in diameter (35 cm). Note also that daughter cysts form within the parent cysts.