Hydatid cysts are formed by the larval stage of Echinococcus granulosus tapeworms. The life cycle is maintained between canines and various farm animals (usually sheep or cattle). Adult worms inhabit the canine small intestine, and eggs are passed in the stool. Farm animals become infected when they feed upon stool-contaminated material. The life cycle is completed when dogs or other canines ingest larval cysts formed in infected farm animals. Humans are infected from inadvertent ingestion of canine fecal material and are considered accidental hosts.
Hydatid cysts most commonly affect the liver and the lungs. Most patients who are infected have no symptoms until the cysts rupture or are large enough to produce mass effect. Diagnosis is centered upon ultrasonography and serologic testing. Changes in farming practices have led to a marked decline in most industrialized countries, but they remain common in many developing areas. Most cases in the United States are immigrants from endemic regions.
Management and Disposition
Hydatid cysts are often an incidental finding when x-rays, CT scans, or ultrasounds are done for other purposes. These patients can be referred for follow-up. Patients with symptomatic cysts may need admission. Depending on cyst size and location, treatment may include percutaneous aspiration, surgical resection, or pharmacotherapy. Care must be taken with surgery to avoid spillage of cysts, which may lead to anaphylaxis.
Liver cysts may produce obstructive jaundice, abdominal pain, or cholangitis.
Cysts are slow growing with an estimated average growth of 1 to 1.5 cm per year.
A chronic cough, pleuritic chest pain, hemoptysis, and dyspnea may be seen with lung involvement.
Although cerebral involvement is uncommon, it is seen more often in children.
Hydatid Cyst Radiograph. Chest x-ray showing multiple hydatid cysts. (Photo contributors: Rob Greidanus, MD, and Universidad Peruana Cayetano Heredia, Lima, Peru.)
Hydatid Cyst CT. Scan demonstrating large hydatid cyst in the liver. (Photo contributors: Seth W. Wright, MD, and Universidad Peruana Cayetano Heredia, Lima, Peru.)
Hydatid Cyst CT. Multiple echinococcal cysts are seen in the chest and liver of this middle-aged Latin American man with chronic cough, chest pain, and hemoptysis. (Photo contributor: Lawrence B. Stack, MD.)