There are two forms of hydatid disease, the most common being Echinococcus granulosus, which causes cystic hydatid disease. Echinococcus alveolaris is a much rarer form and is characterized by an infiltrative pattern of liver involvement.
Hydatids may be symptom less and are detected as incidental findings on radiological investigations for other conditions. The most common symptoms are right upper quadrant pain, jaundice, pruritus and pyrexia. A persistent cough may indicate pulmonary involvement investigation Liver function tests may show either an obstructive or hepatocellular pattern. Full blood examination may reveal a leukocytosis or eosinophilia. There are numerous serological tests available. The most sensitive and specific test is immunoelectrophoresis, which is not only diagnostic but is an indicator of the response to treatment. Radiological tests to assess the size and location of the cyst include ultrasound and CT scan. ERCP or magnetic resonance cholangiopancreatography (MRCP) may be indicated to detect biliary connections or bronchobiliary fistulas.
Small (<2–3 cm) asymptomatic cysts, which are deep in the parenchyma, require no treatment. Complications in this group are rare. These patients however need regular follow-up.
Drug therapy may be used alone or in conjunction with surgical procedures. Mebendazole or albendazole may be used in patients with hydatid disease who are regarded as poor risk for surgery or with widely disseminated disease. It may be also be used by percutaneous injection under ultrasound localization directly into the cyst. These drugs may also be administered either before or after definitive surgery to minimise the risk of recurrence. Prolonged courses over 6–12 weeks are usually required. Medical therapy alone is successful in 30 to 50% of cases. These drugs may be toxic to the liver and bone marrow and require careful monitoring.
The principles of surgical management include (a) complete neutralisation and removal of the parasite components, including the germinal membrane, scolices and brood capsules; (b) prevention of contamination or spillage to prevent anaphylaxis or recurrence and (c) management of the residual cavity. Procedures may include liver resection, with total excision of the cyst, including the capsule (pericystectomy).
This is rarely indicated and is suitable for peripheral or pedunculated cysts. Scolicidal agents are frequently injected into the cyst prior to manipulation to destroy active components and prevent recurrence if spillage occurs. Commonly used agents include cetrimide or hypertonic saline. The contents of the cyst are then evacuated. The residual cavity may be filled with saline and closed (capittonage) or obliterated by an omental pedicle, especially in infected cysts. Biliary communications may need to be closed and bile duct explored to remove hydatids causing biliary obstruction.