Coenurosis: Taenia multiceps (Bladderworm)

Human coenurosis represents infection by a coenurus, the larval stage of any one of four species of tapeworm: Taenia multiceps, T. serialis, T. brauni, and T. glomerata. The coenurus, or larval stage of these four species, has multiple protoscolices, which microscopically distinguishes it easily from the cysticercus of T. solium, which has only a single scolex. These adults of Taenia spp. live in the intestines of dogs and other canines and pass eggs which are then ingested by grazing animals, usually sheep, goats, and rabbits. Oncospheres escape from the eggs and form coenuri in various tissues. Localization in the CNS of sheep causes the "staggers."

Most human infections resulting in cerebral coenuri have occurred in West, East, and South Africa, France, England, Brazil, and the United States. Coenuri cysts in the brain may cause ventricular obstruction, giving rise to raised intracranial pressure. Patients with coenurosis present with headache and papilledema. The cysts have been responsible for jacksonian epilepsy, hemiplegia, monoplegia, and cerebellar ataxia. When the spinal cord is affected, there may be spastic paraplegia. Ventriculography, CT, or MRI may show dilatation of the ventricles, but there are no specific diagnostic findings. On CT scans viable cysts appear as lucent lesions surrounded by a contrast-enhanced peripheral rim. Multiple echo MRI sequences reveal that the intensity of the cyst contents is similar to that of CSF.

The genus Diphyllobothrium includes more than 50 species of tapeworm. Diphyllobothrium latum was the first to be recognized and is most common in Northern Europe; however, the same name is used to describe the cause of clinical diphyllobothriasis in North America, regardless of which of the 13 species found in humans is responsible. This is not an uncommon infection, with perhaps over 9 million cases occurring worldwide. The experts debate whether Diphyllobothrium belong to the same genus as Spirometra.

The infection is also known as fish tapeworm disease or broad tapeworm disease. Although most common in the Northern Hemisphere, particularly in Europe and the more northern American and Canadian states and provinces, the tapeworm has a worldwide distribution and in the tropics has been found in East and West Africa (Botswana, Angola, Uganda, Madagascar), Indonesia and New Guinea, and parts of South America. The intermediate hosts are freshwater crustaceans and freshwater fish. Infection of fish and subsequently fish-eating mammals (bears, dogs, and other carnivores) and humans may occur wherever sanitation is poor and human waste is dumped into rivers and lakes. The transport of unfrozen fish from infected waters has caused infection in humans who are far from the endemic areas. When a human (the normal definitive host) or other mammal eats raw infected fish, the encysted sparganum or larva within the fish musculature is released and develops into an adult tapeworm within the intestine. Adult worms can live for up to 29 years.

Fortunately, the fish tapeworm's only significance for radiologists is that it should be recognized as yet another cause of eosinophilia and anemia and that heavy infection with the long (3-10 m) adult worms may cause mechanical intestinal obstruction.

Hymenolepis nano, Hymenolepis diminuta, and
Inermicapsifer madagascariensis

These tapeworms are widespread in the tropics and all may affect man (Hymenolepis nana has no other host except mice); in many tropical countries they are more common than either T. solium or T. saginata. There are no clinical symptoms or radiological signs unless the worm load is very heavy, in which case anorexia, diarrhea, abdominal pain, and headache may occur. Rarely, seizures have been reported. At least one-third of patients will have eosinophilia. Intestinal obstruction from blockage or volvulus has occurred, because there may be thousands of these tiny worms within the human intestine.