70. Hydatid disease of the liver

1. Definition

• Hydatid disease (echinococcosis) → zoonotic infection by the larval stage of the tapeworm Echinococcus
• Cystic echinococcosis → E. granulosus; slow-growing fluid-filled cysts, most in the liver
• Alveolar echinococcosis → E. multilocularis; infiltrating, tumour-like mass; behaves like a cancer
• Polycystic (neotropical) → E. vogeli, E. oligarthrus (South America; rare)

2. Epidemiology

• Endemic in sheep-farming regions → Mediterranean (including Bulgaria, Greece, Turkey), Middle East, Central Asia, China, North Africa, South America (Argentina, Chile, Peru), Australia
• Bulgaria → one of the highest rates in the European Union
• Over 1 million people infected worldwide
• Liver about 70%, lung about 20%; rest → spleen, kidney, brain, bone, muscle, heart
• Single cyst in about 75%; right lobe more than left
• Alveolar → Central Europe (Alps), China, Russia, Alaska; rarer, but more lethal (untreated mortality over 90% at 10 years)

3. Aetiology and risk factors

Life cycle (E. granulosus)

1. Definitive host → dog (and other canids); adult tapeworm (3–6 mm) in the small bowel
2. Eggs pass in dog faeces onto grass and soil
3. Intermediate host → sheep (cattle, goats, pigs) eats eggs
4. Embryo (oncosphere) hatches in the gut, crosses the wall, reaches the liver through the portal vein (first filter) or the lung (second filter)
5. Larva forms a hydatid cyst
6. Dog eats infected sheep offal → cycle completes
7. Humans → accidental intermediate host (dead end); infected by eating eggs from contact with dogs, contaminated food, water, vegetables
8. Alveolar (E. multilocularis) → foxes (definitive), rodents (intermediate)

Risk factors

• Rural life, sheep farming, close contact with dogs
• Home slaughter of animals; feeding offal to dogs
• Poor hygiene, untreated water

4. Pathogenesis

• Cyst structure (three layers):
  1. Pericyst (adventitia) → fibrous layer made by the host; not part of the parasite
  2. Laminated membrane (ectocyst) → acellular, white, elastic
  3. Germinal layer (endocyst) → inner living layer; makes brood capsules, protoscolices and daughter cysts
• Hydatid fluid → clear, rock-water; highly antigenic; contains hydatid sand (protoscolices)
• Grows slowly → about 1–5 cm a year; symptoms after years
• Rupture:
  • Into the bile ducts (most common; 5–25%) → cholangitis, obstructive jaundice, biliary colic
  • Into the peritoneum → anaphylaxis, secondary peritoneal hydatidosis (protoscolices seed)
  • Into the chest → bronchobiliary fistula (coughing up bile and membranes), empyema
  • Into the bowel, pericardium, vessels (rare)
• Secondary infection → liver abscess
• Each spilled protoscolex can grow into a new cyst → reason for scolicidal agents and careful surgery
• Alveolar → no limiting pericyst; buds infiltrate the liver like a cancer; spreads to lung and brain

5. Classification

WHO-IWGE ultrasound classification (cystic echinococcosis)

• CL → cystic lesion, no visible wall (uncertain; may not be hydatid)
• CE1 → active; simple cyst with visible double wall; "hydatid sand" (snowflake sign)
• CE2 → active; multivesicular with daughter cysts ("honeycomb", "rosette")
• CE3a → transitional; detached membrane ("water lily sign")
• CE3b → transitional; daughter cysts inside a solid matrix
• CE4 → inactive; solid, heterogeneous ("ball of wool")
• CE5 → inactive; solid with calcified wall
• (Gharbi classification I–V is the older equivalent)

Alveolar echinococcosis

• WHO PNM staging (parasite extension, neighbouring organs, metastases)

6. Clinical picture

Symptoms

• Most are asymptomatic for years; found by chance on ultrasound
• RUQ pain or discomfort, fullness, mass
• Dyspepsia, nausea (pressure)
• Complications:
  • Jaundice, fever, colic → rupture into the bile ducts (cholangitis)
  • Anaphylaxis → urticaria, wheeze, shock after rupture or trauma
  • Fever, rigors → infected cyst
  • Cough with bile (biloptysis) → bronchobiliary fistula
  • Portal hypertension, Budd-Chiari (large cysts near the veins; rare)
• Alveolar → RUQ pain, jaundice, weight loss, hepatomegaly (like liver cancer)

Signs

• Hepatomegaly or smooth RUQ mass
• "Hydatid thrill" (historical)
• Jaundice, fever
• Urticaria, eosinophilia signs

7. Diagnosis

• Ultrasound → first test; WHO stage; daughter cysts, membranes, calcification; screening in endemic areas
• CT → size, number, site, relation to vessels and ducts, extrahepatic cysts; surgical planning
• MRI and MRCP → cyst-biliary communication, membrane detail
• Serology → ELISA, indirect haemagglutination, immunoblot (Western blot) for confirmation
  • Negative in up to 10–40% of liver cysts (higher in lung, calcified or intact cysts); a negative test does not exclude it
• FBC → eosinophilia (in 25–40%; more after leakage)
• LFT → cholestasis with biliary rupture
• Chest X-ray or CT chest → lung cysts (in 20%)
• ERCP → biliary rupture: membranes in the CBD; clears the duct
• Diagnostic aspiration is not done blindly (anaphylaxis, spillage); only as part of PAIR with albendazole cover
• Casoni skin test → obsolete

8. Differential diagnosis

• Simple liver cyst (thin wall, no septa; serology negative)
• Liver abscess (pyogenic or amoebic)
• Biliary cystadenoma or cystadenocarcinoma (mucinous cystic neoplasm)
• Polycystic liver disease
• Haematoma, biloma
• Necrotic tumour, metastases
• Alveolar → hepatocellular carcinoma, cholangiocarcinoma

9. Treatment

• Choice depends on WHO stage, size, site, complications, patient fitness and local expertise (WHO-IWGE expert consensus)

Conservative

• Albendazole (benzimidazole; first-line drug):
  • 10–15 mg/kg/day (about 400 mg twice daily) with a fatty meal
  • Alone → small CE1 and CE3a cysts under 5 cm; inoperable or multiple cysts; cure in about 30%, response in 50–70%
  • Perioperative cover → start 1 week to 1 month before surgery or PAIR, continue 1–6 months after (lowers recurrence from spillage)
  • Side effects → raised liver enzymes, neutropenia, alopecia; monitor LFT and FBC; avoid in pregnancy
  • Mebendazole, praziquantel (added before surgery) → second-line
• Watch and wait → inactive CE4 and CE5 (uncomplicated): ultrasound follow-up, no treatment
• PAIR (percutaneous) → CE1 and CE3a, 5–10 cm; unfit for surgery or patient's choice:
  1. Puncture under ultrasound (through a rim of liver tissue)
  2. Aspiration of fluid; check for bile (bile-stained fluid → stop; cyst-biliary communication)
  3. Injection of a scolicide → hypertonic saline 20% or 95% ethanol, left 15–20 minutes
  4. Re-aspiration
  5. Under albendazole cover; resuscitation ready for anaphylaxis
  6. Contraindications → CE2 and CE3b (multivesicular), cysts communicating with bile ducts, superficial cysts, inactive cysts, lung cysts
  7. Modified catheterisation techniques for larger or multivesicular cysts in expert centres
• Anaphylaxis → adrenaline, steroids, antihistamines, fluids

Surgical

• Indications → large CE2–CE3b cysts, multiple daughter cysts, cyst-biliary communication, superficial cysts at risk of rupture, infected or ruptured cysts, pressure on major structures, failed PAIR
• Protection of the field:
  • Pack around the cyst with swabs soaked in a scolicide (hypertonic saline 20%; avoid formalin)
  • Aspirate first through a closed system, inject scolicide, wait, then open
• Conservative (tissue-sparing) surgery:
  1. Evacuate the contents, laminated membrane and daughter cysts (endocystectomy)
  2. Inspect for bile leaks; suture any biliary openings
  3. Partial pericystectomy (deroofing; unroofing)
  4. Deal with the cavity → omentoplasty (fill with omentum), capitonnage (sutured closure), external drainage
  5. Simpler, but higher recurrence and bile leak
• Radical surgery:
  • Total pericystectomy (closed or open) → removes the cyst with its pericyst
  • Liver resection (segmentectomy, hepatectomy) → peripheral or large cysts that destroy a segment
  • Lower recurrence; more bleeding risk near major vessels
• Laparoscopic → selected peripheral, anterior cysts in expert hands
• Biliary rupture → ERCP with sphincterotomy to clear membranes from the CBD (before or after surgery); persistent biliary fistula → ERCP stent
• Lung and liver cysts together → right thoracotomy for both, or staged (lung first)
• Alveolar echinococcosis → radical liver resection with clear margins (as for cancer) plus albendazole for at least 2 years; liver transplantation in selected unresectable cases; lifelong albendazole if not resectable

Conservative: prevention

• Deworm dogs (praziquantel); do not feed offal to dogs; control slaughter; hand washing; vaccination of sheep (EG95)

10. Complications

• Rupture into the bile ducts → cholangitis, obstructive jaundice, pancreatitis
• Intraperitoneal rupture → anaphylaxis, secondary hydatidosis
• Infection → liver abscess
• Bronchobiliary fistula, pleural empyema
• Portal hypertension, Budd-Chiari syndrome (rare)
• Treatment:
  • Recurrence (2–25%; higher after conservative surgery)
  • Postoperative bile leak and external biliary fistula (most common surgical complication)
  • Residual cavity infection, abscess
  • Sclerosing cholangitis → scolicide (formalin, hypertonic saline) passing into the ducts
  • Anaphylaxis during PAIR or surgery
  • Albendazole → liver toxicity, bone marrow suppression