Hydatid Infection of the Liver

Hydatid Infection of the Liver

• Echinococcosis, also known as hydatid disease, is a worldwide zoonotic parasitic disease caused by a small tapeworm of the genus Echinococcus.
• Echinococcus granulosus causes cystic echinococcosis (CE), while Echinococcus multilocularis causes alveolar echinococcosis.
• The definitive host is a canine species, commonly dogs.
• The gravid worm releases embryonated eggs in dog feces (infective stage).
• Intermediate hosts ingest these eggs, which commonly include sheep, swine, horses, camels, and humans (accidental intermediate hosts).
• Eggs hatch in the intermediate host's intestines, releasing oncospheres.
• Oncospheres penetrate the host's intestines, enter the portal circulation, and travel to the liver.
• Oncospheres then enter the general circulation and travel to other organs.

Pathogenesis and Cyst Wall Components

• The liver and lungs are the primary sites of hydatid cysts, with the liver being affected in 75% of cases.
• The growing cyst and inflammation cause liver compression, leading to pericyst formation (host tissue).
• A tough, fibrotic pericyst prevents complete collapse of the residual cystic cavity after therapeutic removal.

Cyst Components

• The inner layer of the hydatid cyst is the lamellar layer.
• The germinal layer within this inner layer produces daughter cysts, which can detach or burrow into surrounding tissues.
• Intra-cystic contents in older cysts degenerate into a gelatinous, amber-colored matrix, often appearing as a pseudotumor and requiring differentiation from a pyogenic abscess.
• Endocyst calcification indicates a dead cyst.
• Pericyst calcification alone, though detectable with imaging, does not necessarily signify a dead cyst.

Diagnosis

• Diagnosing hydatid cysts involves confirming the diagnosis and excluding other cystic liver lesions.
• Liver hydatid cysts can present in three forms: asymptomatic (discovered incidentally), uncomplicated (due to size/location), and complicated (due to infection/rupture into surrounding structures).

Complicated Cysts

• Complicated cysts involve rupture into bile ducts, surrounding organs, or body cavities, possibly presenting with pain, shock, or anaphylaxis features.
• Infection can cause cysts to behave like liver abscesses, requiring appropriate treatment.
• Pressure on the portal vein can lead to extrahepatic portal vein obstruction (with splenomegaly and enlarged collaterals/varices).
• A large cyst can cause inferior vena cava obstruction, resulting in dependent edema and dilated flank veins.

Serum Tests

• ELISA tests for antibody detection are widely available, but specificity can be limited due to cross-reactions with other parasites.
• Currently, there are no serological tests that differentiate between Echinococcus subspecies.
• ELISA positivity increases with the duration of the infestation and the individual's age.

Imaging

• Ultrasound is a highly effective method for diagnosing hydatid cysts.
• CT and MRI scans are necessary to precisely define the cyst's location and identify potential complications (especially cyst-biliary communication).

Treatment

• Current treatment options may include drug therapy, puncture aspiration injection reaspiration (PAIR), surgery, or watchful waiting.

Drug Treatment

• Albendazole is the preferred drug for hydatid cyst management, but it's typically used alongside other modalities, not as a stand-alone treatment except if surgery is contraindicated.
• Albendazole dosing is 10-15 mg/kg daily for 8-12 weeks.
• Praziquantel does not increase albendazole levels within the cyst.
• Drug bioavailability increases when taken with a fatty meal and avoiding high intragastric pH (e.g., by avoiding proton pump inhibitors).
• Albendazole has a favorable safety profile. Common side effects are transient increases in liver enzymes and leukopenia, with complete hair loss being very rare and reversible.

Puncture Aspiration Injection Reaspiration (PAIR)

• PAIR is image-guided (typically ultrasound) percutaneous drainage of intra-abdominal hydatid liver cysts.
• PAIR treatment involves scolicidal solutions (like hypertonic saline) to kill cystic elements.
• PAIR-D is used for large cysts (>5 cm) requiring a drainage tube.

PAIR Indications and Contraindications

• Indications include multiple accessible cysts, infected cysts, pregnant women and other patients unfit/refusing surgery avoiding chemotherapy alone.
• Contraindications include non-co-operative patients, non-accessible cysts, mature calcified cysts, and cysts with biliary communication.

Pre and Post PAIR Treatment

• Pre-treatment with albendazole (at least 4 hours to 1 week) is advised, and post-treatment drug continuation for at least a month afterwards is usually recommended.
• Treatment duration is contingent on the cyst size and consistency observed in follow ups.

Surgical Treatment

• Surgery is the definitive treatment for complicated cysts and considered definitive treatment option for hepatic hydatid disease.
• Aims of surgery include total removal of infected components, preventing spillage and managing any residual cavity/cystobiliary communication.
• Indications for surgery include active cysts (with multiple daughter cysts or septae/honeycomb appearance), cysts with fluid collections and membrane detachment, large cysts (>10 cm), or difficult/recurrent cases after prior surgery/PAIR procedures.

Wait and Watch

• Cysts containing a heterogenous or solid matrix can remain inactive/dormant for prolonged periods.
• These cysts can be safely monitored by ultrasound until the appearance of complications (such as pain).