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Purely medical treatment has been used occasionally when surgery is contraindicated or in widely disseminated disease, but the patient must be monitored closely because of the danger of communicating or direct rupture. It is possible that direct rupture as a result of treatment of intraperitoneal and similar cysts may be a benign process since the ruptured cyst is probably sterile and the fluid probably has lost its antigenicity by the time of rupture. Furthermore, there is no danger of a biliary leak or bleeding after rupture of such lesions. This suggestion must, however, be tested in a controlled study before acceptance.

Evaluation of chemotherapy is gauged by the effectiveness of cyst response, as shown by ultrasonography, CT, MRI and, in the chest in particular, conventional radiography. A successful response is disappearance or decrease in size of the cyst, or deformation and calcification of all cysts (Figs. 3.154B,C thru 3.155). A partially successful response is the above response in some but not all cysts, including increased density of cyst contents, hyperechoic structures, unsharpness of the cyst wall, collapsed parasitic membranes, or deformation of cysts and cyst wall with or without pericystic edema and calcification. An unsuccessful response is shown when there is no change in the appearance of cysts. Each cyst has to be evaluated separately.

Over 1000 well-documented cases of cystic hydatidosis have been treated with benzimidazoles (mebendazole and albendazole) as of 1997. After 12 months, 30% of patients show cyst disappearance (i.e., cure), 30-50% show degeneration of cysts and/or significant size reduction (i.e., improvement), but 20-40% exhibit no morphological changes in the cysts, indicating failure. Some of the treated patients suffer relapses, but these are sensitive to retreatment in a high proportion of cases (up to 90%). Local surgical drainage of cysts has also been successfully used (Fig. 3.154A), but has been largely replaced by PAIR.

PAIR has been widely used by Italian groups and others in endemic areas in Africa, using ultrasound and serology (Echinostrip) for diagnosis. This method seems especially effective in developing countries where, in isolated areas, no equipment or facility for surgery exists, and ultrasound combined with a simple technique of serology allows large-scale screening of populations without the need for a fully equipped laboratory. Nevertheless, PAIR should be performed only by experienced physicians and ideally with a surgical backup team prepared to deal with complications. PAIR treatment should be accompanied by chemotherapeutic coverage to minimize recurrence. However, further long-term, properly controlled studies are required to evaluate the efficacy and potential risks of this method.

Although hydatid disease is common, individual series are usually not large. For this reason an international medical hydatid registry employing uniform nomenclature and consistent reporting would be valuable for assessing the outcome of various forms of medical, surgical, and interventional management.

Fig. 3.155 Follow-up studies of the Saudi patient in Fig. 3.56 after surgery and chemotherapy. CT scans of the abdomen and pelvis 4 months after partial surgical resection and treatment with albendazole show marked improvement. Several remaining hydatid cysts are noted in the liver, abdomen and pelvis. (Courtesy of Dr. von Sinner.)


POLYCYSTIC HYDATID DISEASE (E. vogeli and E. oligarthus.

Polycystic hydatid disease is an infection caused by the larval stages of the tapeworm Echinococcus vogeli and, rarely, by E. oligarthus. E. vogeli infection is most common in rural areas of Panama, Ecuador, Colombia, Bolivia, Brazil, Argentina, Venezuela, and Costa Rica. It was first recorded in humans in Colombia in 1979. The first recorded human infection with E. oligarthus was an orbital cyst in a Venezuelan woman in 1989. E. oligarthus spreads further south than E. vogeli, as far as sub-Antarctica. Exact figures of incidence are perhaps unreliable because it is probable that some cases attributed to E. oligarthus were in fact first caused by E. vogeli.

The intermediate host is the paca (alpaca); this grazing mammal is one of the New World camels, many of which are domesticated. In one survey, 76% of pacas were infected with E. vogeli, and 3% with E. oligarthus. Domestic and bush dogs are hosts to E. vogeli, which together with E. oligarthus is also found in wildcats (ocelots, jaguars, pumas). The life cycle of E. vogeli is similar to E. granulosus, but there are minor differences in size and particularly in the shape of the hooks. The larvae develop into relatively larger fluid-filled cysts which are usually polycystic, unlike the unicysts of E. granulosus.

Polycystic hydatid disease is most common in the liver, followed by the lung, mesentery, spleen, and pancreas. Polycystic hydatid disease should be distinguished from a single cyst with multiple septa or daughter cysts, and from the many small grape-sized cysts of alveolar hydatid disease. Although they cannot be separated by serology, there is good reason to try to distinguish between E. granulosus and E. vogeli because the latter, the polycystic pattern, grows more rapidly and becomes clinically apparent sooner. E. oligarthus infection is very rare in humans, and has similar characteristics to E. vogeli.

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