Diagnosis

Cystic Echinococcosis

The diagnosis of E. granulosus (cystic hydatid disease) is best made by identifying the presence of a cystlike mass in a person with a history of exposure to sheepdogs in areas where the parasite is endemic. Cystic echinococcosis must be differentiated from benign cysts, cavitary tuberculosis, mycoses, abscesses, and benign or malignant neoplasms. Noninvasive imaging techniques such as CT scans, MRI, and ultrasound imaging are all used for detecting and for defining the extent and condition of avascular fluid-filled cysts in most organs. These techniques have proved valuable for diagnosis and preoperative evaluation by staging the condition of the lesion, the extent of the lesion in reference to other organs and vital structures, and identifying the presence of additional occult lesions. Radiography permits the detection of hydatid cysts in the lungs; however, in other organ sites, calcification is necessary for visualization. Ultrasonography has been widely used for screening, clinical diagnosis, and monitoring of treatment of liver and intraabdominal cysts.

Enzyme-linked immunosorbent assay (ELISA) and the indirect hemagglutination test are highly sensitive procedures for the initial screening of serum. Specific confirmation of reactivity can be obtained by demonstrating echinococcal antigens by immunodiffusion (arc 5) procedures or immunoblot assays (8-, 21 –kD bands).

Alveolar Echinococcosis

Alveolar echinococcosis closely mimics hepatic carcinoma or cirrhosis and is typically present in people of an advanced age. Plain films show hepatomegaly and characteristic scattered areas of radiolucency outlined by calcific rings 2 to 4 mm in diameter. The usual CT image of E. multilocularis infection is that of indistinct solid tumors with central necrotic areas and perinecrotic plaquelike calcifications. Serologic test results are usually positive at high titers. Comparing a patient’s titers with both purified-specific and shared antigens permits the serologic discrimination between patients infected with E. multilocularis and those infected with E. granulosus.

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Disease

Cystic Echinococcosis

The incubation period of cystic echinococcosis is often prolonged for several years and most cases of cystic echinococcosis remain asymptomatic until the cysts reach a large enough size to cause dysfunction. Most primary infections in humans consist of a single cyst. The liver is the most common site of the hydatid cysts, followed by the lungs. Cysts in the spleen, kidneys, heart, bone and central nervous system are less common. In secondary echinococcosis, larval tissue spreads from the primary site and new cysts develop after spontaneous or trauma-induced cyst rupture or after release of viable parasite material during invasive treatment procedures.

Signs and symptoms may include hepatic enlargement with or without a palpable mass in the right upper quadrant, right epigastric pain, nausea, and vomiting. Rupture or leakage usually results in acute or intermittent allergic manifestations.

Alveolar Echinococcosis

The primary infection of alveolar echinococcosis is in the liver, but direct extension to contiguous organs, as well as hematogenous metastases to the lungs and brain is not uncommon. Alveolar echinococcosis is inhibited by the host from completing its development and remains in the proliferative stage indefinitely. The larval mass resembles a malignancy in appearance and behavior. In chronic alveolar hydatid infections, the lesion consists of a central necrotic cavity filled with a white amorphous material that is covered with a thin peripheral layer of dense fibrous tissue. Host tissue is directly invaded by extension of the budding and proliferating cyst wall, causing a pressure necrosis of surrounding host tissue. A vigorous inflammatory and fibrous tissue reaction usually surrounds the larval mass. Diagnosis is often delayed until an advanced and inoperable stage; mortality rates have traditionally been high, ranging between 50% and 75%.

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Treatment

Cystic Echinococcosis

In the past, surgery was the only treatment for cystic echinococcal cysts. Chemotherapy, cyst puncture, and PAIR (percutaneous aspiration, injection of chemicals and reaspiration) have been used to replace surgery as effective treatments for cystic echinococcosis. Even with advances in chemotherapy, surgery remains the best treatment option for cystic echinococcosis by removing the cysts and leading to an immediate cure. Although pericystectomy is the usual procedure, simple drainage, capitonnage, marsupialization, and resection of the involved organ may be used depending on the location and condition of the cysts. Surgery is the best treatment for liver cysts greater than 10 cm in diameter, secondarily infected, or if they are located in the brain, lungs, or kidney. Surgery usually involves injection of protoscolicidal chemical solutions into the cyst, followed by evacuation, prior to further manipulations and extirpation of cysts. Additionally, perioperative injection of protoscolicidal chemicals should not be practiced as a routine procedure.

Approximately one third of patients treated with chemotherapy with benzimidazole drugs have been cured of the disease and even higher proportions, between 30-50%, have responded with significant regression of the cyst size and alleviation of symptoms. Small, less than 7 mm diameter, isolated cysts, surrounded by minimal adventitial reaction, respond best. Both albendazole 10 to 15 mg/kg body weight per day (max 800 mg po in 2 doses) in several one-month courses with treatment-free intervals of 14 days and mebendazole 40-50 mg/kg body weight per day continuously have been highly effective. Additionally, chemotherapy can be very effective when used in conjunction with surgery. Albendazole has been administered to patients prior to surgery for the intended purpose of facilitating the safe surgical manipulation of the cysts by inactivating protoscolices, altering the integrity of the cysts membranes, and reducing the turgidity of the cysts. A third treatment option, PAIR (percutaneous aspiration, injection of chemicals and reaspiration), has been shown to be effective.

*Praziquantel may be useful preoperatively or in case of spillage of cyst contents during surgery (Bygott JM, Chiodini PL. Acta Tropica 2009; 111: 95-101).

Alveolar Echinococcosis

Alveolar echinococcosis usually requires radical surgery, chemotherapy, or both. Effective treatment involves mebendazole administered continuously for up to 10 years at doses of 40 to 50 mg/kg body weight per day. This has inhibited progression of alveolar echinococcosis and reduced lesion size in approximately half of treated cases. Albendazole administered for repeated periods of 28 days at doses of 10 mg/kg body weight per day with treatment-free intervals of 14 days produced results similar to those described with mebendazole.

Surgical excision is the only reliable means of cure. In nonresectable cases, albendazole (400mg orally twice a day) has been shown to stabilize and sometimes cure infection. (Moro P, Schantz PM. Int J Infect Dis 2009; 13:125).

More on: Echinococcosis, WHO

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