Taeniasis (tapeworm). Cysticercosis.

Many people are infected with tapeworms, particularly by the beef tapeworm, T. saginata, or the pork tapeworm, T. solium. Cysticercosis is an infection with the larval stage of the pork tape worm (originally named cysticercus cellulosae, before it was known to be the larval form of T.solium). Infection of man by the corresponding larval stage of the beef tape worm is not known.

Taeniasis

Tapeworms occur throughout the world. Human infection results from eating undercooked, or raw, infected meal. There may be no clinical illness or abdominal discomfort, but loss of weight and diarrhoea may occur. There may be a 10% eosinophilia. Multiple tape worms can cause intestinal obstruction. Worms have caused appendicitis.

Taenia saginata is very seldom recognised radiologically or by ultrasound: there may be a long radiolucent line within a column of barium in the lower jejunum and ileum. The adult worm may be extremely long, up to 10m or more, and in extreme cases it is so long that it is seen as a translucent line in the colon as well as in the small bowel. The worm does not absorb barium (it has no alimentary canal).
T. solium has not been identified by imaging.

Cysticercosis

As occurs with so many other parasites, cysticercosis results from swallowing infected food or water. Occasionally, autoinfection in a patient who has a resident tape worm may occur. Except in the brain (or the eye) the cysticercus becomes surrounded by a fibrous capsule, but may remain alive for some years. When it dies the cellular reaction may eventually calcify, usually after about 3 years. Living and dead may occur together. In skeletal muscles, the dead cysts cause few symptoms, but heart block has been recorded in the cardiac conducting tissue. In the central nervous system the scarring may cause epilepsy, and occasionally severe encephalitis and death. If the cerebral ventricular system is blocked, there may be raised intracranial pressure and the clinical symptoms may suggest a cerebral tumour.

The first calcified cysts were recognised radiologically in the 1890s, long before the adult worm. Radiographically the calcified cysticercus is oval or linear and from 4 to 10 mm in length: larger cysts have been reported. The oval cysts lie with their long axis in the line of the muscle (Fig. 43 a). They may be very numerous, particularly in the legs and back, and may be a chance finding seen in the thoracic muscles on a routine chest radiograph. If cysticercosis is suspected, soft tissue radiographs of the upper legs should be obtained. The appearance of the cysts is so characteristic, and in many patients there are so many cysts that the differential diagnosis is straightforward. No other soft tissue calcification resembles this or is present in such large numbers.

In the brain, it is rarely possible to see the calcified cyst on a plain radiograph of the skull. In fact, plain skull radiographs are not likely to be a useful examination in this disease. Soft tissue radiographs of the thighs will provide more confirmation if cysticercosis is suspected as the cause of seizures. However, on CT not only the calcified cysticercus but the

a	Figure 43. Cysticercosis. a) The typical oval calcification of cysticercosis lying in the thigh muscles. (Nigeria) b,c) CT scans of calcified cysticerci, lying periventricularly, but in this patient not causing any other lesions (post contrast). (Egypt)
b
c

multiple cerebral cysts can be visualized in the cortex and the walls of the ventricles (Fig. 43 b). MR will demonstrate the cysts, but not the calcification. The cysts are thin-walled and contain clear fluid and free floating scolices. Some cysts may be quite large, so that the ventricular system is blocked with resulting internal hydrocephalus. Complete obliteration of the aqueduct can occur, but is uncommon. In some cases there will be basal arachnoiditis. Very rarely, there is erosion of the skull by the underlying cyst.

Similarly, spinal cysticercosis can be recognized by CT or MR. The cysts may be intradural or extramedullary, are of different sizes, but usually spherical. They may fragment or become irregular and there may be associated arachnoiditis. Complete spinal canal obstruction can occur, but is uncommon. If CT or MR are not available, myelography will demonstrate intradural and extramedullary filling defects of different sizes, or irregularity of the contrast column and in some cases partial or complete obstruction. Plain radiographs of the spine do not demonstrate the cysticercus.
(Figures number 28,29, 33 a, b, 39 a, b, come from the "Radiology of Tropical Diseases" by Palmer, P.E.S. and Reeder M.M., Springer, Heidelberg, 2nd edition. In press.)

Philip E.S. Palmer, with Stanley P. Bohrer, Carlos Bruguera, Xing-Rong Chen, Mahmoud R. EImeligi, Hassen A. Gharbi, S.B. Lagundoye, M. W. Wachira