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Chapter 48

The Ultrasonography of Tropical Diseases*

S. MINDEL with M. W. WACHIRA

* Note: The sonographic findings and the differential diagnoses in this chapter apply specifically to practice in the tropics.

"The glories of our blood and state are shadows, not substantial things"

James Shirley, 1596-1666
(The Contention of Ajax and Ulysses)

Ultrasonography can provide a remarkable amount of information, sometimes so much that it may be difficult to choose between the many alternative diagnoses for a particular patient, especially if the social and health background of the patient is unfamiliar. The first impression obtained from an ultrasound scan must often be reconsidered and the many factors assessed and given their due weight; further scanning may be necessary to add, or discard, information before reaching a conclusion.

This chapter considers the differential diagnosis of the ultrasound findings resulting from tropical diseases. Unlike most of the others in this book, it is based on the clinical presentation, not disease entities: for example, the mass in the right lower abdomen or the swelling in the neck of a patient who lives in or has visited tropical countries. When a possible diagnosis is reached, more information should be sought in the specific chapter describing that disease. This is important, because there is often geographic variation in both the frequency and the natural history of tropical diseases, and therefore in the ultrasonographic images: it is always wise to have as much information as possible before treating a patient.

Ultrasonography has revolutionized the diagnosis and management of many tropical diseases, with the added advantage that it is neither dangerous (as far as is known, 2001) nor excessively expensive. It can provide accurate information about the abdominal contents and other "soft" organs that might not be obtainable in the absence of far more costly and complex computed tomography (CT) or magnetic resonance (MR) equipment. Ultrasonography will not only indicate the diagnosis in many cases but can guide the biopsy or aspiration, which usually leads to more accurate treatment, as, for example, in hydatid disease or the subperiosteal abscess of osteomyelitis. Although ultrasonography seems simple, it requires good training, experience, and a clear understanding of the anatomy as well as the pathological pattern of each disease. Its accuracy is totally dependent on the skill of the user: it is easy to scan, but equally easy to make mistakes by misinterpreting the image or failing to recognize normal variants or minor abnormalities. It must be emphasized again that ultrasonography is not a magical method which can be used effectively without proper training, and also that inexpensive, poor quality ultrasound equipment may not always provide the required information. As WHO has emphasized, there are minimum standards for ultrasound training and equipment, as there are for every other aspect of clinical medicine. (Refer to the previous Chapter on "Imaging in Small Hospitals" for guidance on the choice of equipment.)

Many tropical diseases have a characteristic ultrasonographic appearance while others mimic more common entities: for example, an apparently straightforward liver abscess may prove to be amebic. It is equally important to remember that even when a patient is in or has been to the tropics, common diseases are still the commonest and an illness may not be due to some exotic parasite or tumor. The clinical history is just as important prior to ultrasonography as before any other imaging procedure. It is essential to know how long the patient has been in the tropics, and in the case of travelers, exactly when and where they visited and what they did there. Did they walk barefoot or swim in local rivers, for example? Reference to the geographic distribution lists at the beginning of the book will prevent the diagnosis of a disease which has never been recorded in the country from which the patient comes or, at least, ensure that such a diagnosis is made with extreme caution.

When practicing in the tropics, or caring for patients from different ethnic backgrounds, another source of confusion may be the inability or reluctance of patients to consult a Western physician.

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Copyright: Palmer and Reeder