Echinococcus granulosus is a dog tapeworm endemic to rural, developing countries.  Prevalence is particularly high in areas of sheep farming (sheep are intermediate hosts), as dogs are often fed sheep viscera.  Humans acquire the infection incidentally after ingesting food or water contaminated by dog feces.  Eggs hatch in the small intestine, penetrate the intestinal wall, and travel to the liver (or, less commonly, lung) where >1 hydatid cysts form.

Many patients remain asymptomatic for years and develop clinical illness only due to large cyst size (>10 cm) or rupture.  Manifestations include right upper quadrant pain, nausea, vomiting, and hepatomegaly.  Rupture may result in fever.  Ultrasound has excellent sensitivity (~95%) and typically shows a large, smooth hepatic cyst often with daughter cysts (internal septations).  Positive serology for E granulosus IgG corroborates the diagnosis (sensitivity ~95%) and usually obviates the need for percutaneous biopsy.  Small cysts (<5 cm) are typically treated with albendazole; larger or complex cysts usually also require percutaneous therapy or surgery.

(Choice B)  Eating contaminated pork may result in a Taenia solium gastrointestinal tapeworm infection.  Humans can transmit tapeworm eggs to others, causing cysticercosis.  Cysticercosis usually affects the brain (seizures) or cerebral ventricular system (intracranial hypertension); liver cysts are uncommon.

(Choice C)  Entamoeba histolytica is often asymptomatic but may cause dysentery/colitis and liver abscess.  Amebic abscess usually manifests with fever, right upper quadrant pain, and a smooth, cystic, subcapsular mass.  This patient is afebrile and has a cystic lesion with daughter cysts, making E granulosus more likely.

(Choice D)  Undercooked fish may transmit liver flukes (eg, Clonorchis sinensis) or fish tapeworm (eg, Diphyllobothrium latum).  Liver flukes typically cause biliary disease (not hepatic cysts).  Fish tapeworm rarely causes symptoms but may cause megaloblastic anemia due to vitamin B₁₂ deficiency.

(Choice E)  Prolonged and excessive alcohol intake increases the risk of hepatocellular carcinoma, which may cause weight loss, abdominal pain, and complications related to rupture or tissue compression.  Imaging typically reveals a dense, irregular mass (not a cystic, smooth mass).

Educational objective:
Echinococcus granulosus is a dog tapeworm endemic to rural, developing countries.  Humans are incidental hosts and usually acquire the infection through the consumption of food or water contaminated with dog feces.  Tapeworm eggs hatch in the small intestine and spread to the viscera (eg, liver, lung), causing hydatid cysts.  Symptoms are initially rare, but hepatic cysts may grow over time, resulting in right upper quadrant pain, nausea, vomiting, and hepatomegaly.  Imaging typically reveals a large, smooth cyst, often with internal septations.