At a glance
Diagnosis varies depending on the infecting species. The primary infection of alveolar echinococcosis is in the liver, usually the right lobe. The liver is the most common site of hydatid cysts, followed by the lungs, in patients with cystic echinococcocis.
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, usually the right lobe, 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%.
Resource
Diagnosis
Cystic Echinococcosis
The diagnosis of E. granulosus infection (cystic hydatid disease) is suggested by identification of a cyst-like 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 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 intra-abdominal cysts. Cyst viability cannot be reliably determined with radiography or parasite antigen detection; calcification can be present in all stages of cysts.
Serologic tests, such as enzyme-linked immunosorbent assay (ELISA) and indirect hemagglutination test, are highly sensitive methods for detecting infection. Specific confirmation 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 more commonly diagnosed in people of an advanced age. Plain radiographs 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 plaque-like 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.