Cystic hydatid disease (CHD) is most common among people who raise sheep and cattle in countries of the temperate zones, including South America, the entire Mediterranean region, southern and central Russia, central Asia, Australia and parts of Africa. Certain activities undertaken by humans facilitate the transmission of the strain and hence increase the risk that humans will be infected. The widespread rural practice of feeding dogs with the viscera of home-butchered sheep is one of the most important factors. Dogs infected with tapeworms pass eggs in their feces, and humans become infected through fecal-oral contact, particularly in the course of playful and intimate contact between children and dogs. Cestode eggs adhere to hairs around the infected dog's anus and are also found on the muzzle and paws. Indirect transfer of eggs, either through contaminated water or uncooked food or through the intermediary of flies and other arthropods, may also transfer the disease to humans. The rate of growth of the cyst is highly variable and ranges from 1 to 5 cm a year [18].
The diagnosis of CHD has previously been based on a history and clinical findings that are compatible with the disease; the clinical findings are too nonspecific to be diagnostic. Skin tests and serologic tests are helpful [5]. Currently, the diagnosis of hydatid disease has been greatly facilitated by US, computed tomography (CT) and MRI. Ultrasound is the method of choice for searching for the pathognomonic criteria of the hydatid cysts [4].
A sensitive and specific serological test is essential for a preoperative diagnosis of hydatid disease [11]. In order to confirm the diagnosis, serological tests, including direct hemagglutination, latex agglutination, immunoelectrophoresis, skin tests and ELISA, are widely used; however, all serological tests are associated with false-negative and false-positive results. Therefore, positive serological results do not confirm the diagnosis of hydatid cyst, and negative results do not exclude it [4]. Infection suspected on the basis of imaging studies (USG, CT, MRI) may be confirmed by specific enzyme-linked immunosorbent assay and Western blot serology, confirming exposure to the parasite. Serology is 80 to 100% sensitive and 88 to 96% specific for liver cyst infection, but less sensitive for lung (50 to 56%) or other organ involvement (25 to 56%). Assays are under development using recombinant Echinococcus antigens, which may provide better specificity for diagnosis. Imaging remains more sensitive than serodiagnosis, and a characteristic scan in the presence of negative serologic results should still suggest the diagnosis of echinococcosis [13]. For a specific serologic diagnosis, Guillermo Ramos et al. has suggested that their experience favors the immunoglobulin G enzyme-linked immunosorbent assay and immunoelectrophoresis [16].
Negative serology would indicate ultrasound-guided aspiration of cyst fluid for cytological verification or enzyme immunoassay. Discrepancies between radiological imaging and serological diagnosis are best resolved by cytology of the drained fluid and/or histopathological examination of the excised cyst [11].
Fine-needle aspiration biopsy (FNAB) using teflon-covered needles with a US visible marker may be very useful for the definitive diagnosis. FNAB is a very important technique in the differential diagnosis of cystic echinococcosis [21]. Saenz et al. reported that fine-needle biopsy appears to be a safe diagnostic approach in the evaluation of suspected hydatid disease [17]. Smears made from aspirated hydatid cyst fluid may show scolices, hooklets or remnants of laminated membrane. Scolices exhibiting suckers and rows of hooklets resemble miniature blunt heads of tapeworms. Hooklets, which often float free within the fluid, are refractile and stain brilliant purple with a Ziehl-Neelsen stain. Laminated membrane stains pink in Papanicoloau smears, black with Gomori's methenamine silver, pink with Best's carmine and is well demonstrated with a PAS stain [22]. Smears of fine-needle aspiration cytology (F.N.A.C) fluid shows protoscolices, fully developed scolices with rostellum and scattered hooklets, pathognomonic of Echinococcosis [1, 14].
Performing aspiration on the cyst for diagnosis has not been advised because of the potential to precipitate acute anaphylaxis or to spread daughter cysts. However, some argue that no sequelae were observed that could be attributable to aspiration if done for the diagnosis of hydatic cyst [12]. Agarwal et al. reported that one patient went into anaphylactic shock following the liver fine-needle aspiration procedure [1]. Saenz-Santamaria et al. reported that no complications were encountered [17].
Surgery is the most important treatment for hydatid cyst. The surgeon must avoid spilling the contents. These cysts frequently induce secondary inflammatory reactions and adhesions to the surrounding tissues, which sometimes make total removal of the cyst difficult. It has been suggested that silver nitrate (0.5%) or hypertonic saline solution (20%) can be injected into the cyst to prevent possible acute allergic reactions and formations of secondary cysts caused by the spillage of the contents. Although the traditional choice of treatment for hydatid disease is surgery, in the recent literature, there are several reports on percutaneous treatment of abdominal and pulmonary hydatid cyst as an alternative to surgical treatment [3]. They reported lower rates of morbidity and mortality and less recurrence [2, 3]. Percutaneous treatment of head and neck hydatid cyst has not been performed so far.
Medical treatment alone is indicated for the following: patients with multiple organ involvement, patients with a cyst in an inaccessible location, patients with a general condition that makes surgery an unacceptable risk and patients with surgical spillage of cyst contents. Although long-term medical treatment with mebendazole or albendazole has been used in the last 15 years, the results are still controversial. Medical treatment may be tried if surgery is not possible because of the general condition of the patient. However, the results are unpredictable.
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