Tropical Diseases of Interest to the Radiologist

Abstract

The airplane and the world-wide scope of our present conflict have resulted in the exposure of large numbers of our countrymen to tropical diseases of various kinds. Clinical information concerning many of the diseases is still relatively limited and radiological knowledge even more so. The following data, however, are reasonably well established, and may be of some value to radiologists called upon to examine persons exposed to the diseases in question. Malaria: This is by far the most important tropical disease at the present time. The only reason for mentioning it in a radiological discussion is that a small number of persons will return to this country during a remission, and will be sent for x-ray examination of the abdomen for one reason or another (gastro-intestinal studies, urological studies, etc.). The patient may fail to give a history of malaria and occasionally may be unaware that he has had the disease. Careful examination of the plain films may reveal an enlarged spleen, which should always be noted. We have seen three instances in which a diagnosis of malaria was first suggested by the radiologist on observing a considerably enlarged spleen in a plain film of the abdomen. Needless to say, there are many other diseases and conditions in which splenomegaly is found, but this observation may lead to a suitable blood study and thereby establish an important diagnosis incidental to the condition from which the patient is suffering. Filariasis: There are some eight types of filariae which infect man. The most important is F. bancrofti (or Wuchereria bancrofti), which causes that variety of filariasis complicated by elephantiasis. Persons returning from Samoa and certain other South Pacific areas may be found to have localized areas of lymphangitis on the upper arms or upper legs, with or without a history of testicular or scrotal swelling. Microscopic examination of an enlarged regional lymphatic or lymph node in some of these cases will reveal the adult filarial worm (which may reach as much as 6 em. in length); in other cases examination of the blood may reveal the microfilariae. After a variable number of months, or possibly years, some of the filariae die and become calcified, producing small recognizable opacities in roentgenograms of involved areas, notably the subcutaneous tissues, the lymph nodes and the scrotal lymphatics (1). They appear as small linear or dot-like shadows, often about 1 mm. in diameter, or 1 × 4 mm. in length, and not so large as the usual phlebolith. The next most important type of filariasis is that due to Onchocerca volvulus (the “blinding filaria”), which causes subcutaneous nodules (especially on the head), and sometimes impaired vision. A rare type of infestation is loasis, due to a filaria called Loa loa, which causes somewhat similar changes; this particular filaria may be found under the conjunctiva.