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Hydatid Cyst of the Liver (Hepatic Echinococcosis)

1. Aetiology & Causative Organisms

Hydatid disease (echinococcosis) is a zoonosis caused by the larval stage of the tapeworm Echinococcus. Three species are clinically relevant:

Species	Disease	Features
E. granulosus	Cystic echinococcosis	Most common; well-defined fluid-filled cysts
E. multilocularis	Alveolar echinococcosis	Highly invasive; solid masses mimicking carcinoma; mortality ~90% if untreated
E. vogeli	Polycystic echinococcosis	Intermediate aggressiveness; polycystic lesions

2. Epidemiology

Endemic in sheep-raising regions: Mediterranean Europe, Middle East, Africa, Far East, South America, Australia, New Zealand
Dogs are the definitive host; sheep are the major intermediate host (also yaks, goats, camels)
Humans are accidental intermediate hosts — no human-to-human transmission
Diagnosed equally in males and females; average age ~45 years

3. Life Cycle & Pathogenesis

Dog (definitive host)
  ↓ eggs shed in feces
Contaminated food/water/vegetables
  ↓ ingested by humans
Small intestine → eggs hatch → oncospheres released
  ↓ penetrate intestinal mucosa
  ↓ enter bloodstream/lymphatics
Liver (70%) > Lungs (20%) > Kidney, Spleen, Brain, Bone
  ↓ vesiculation
Hydatid cyst develops

Cyst wall structure (3 layers):

Outer adventitial (pericyst) — host-derived fibrous capsule; can calcify
Middle ectocyst (laminated layer) — acellular, gelatinous outer worm-derived membrane
Inner endocyst (germinal layer) — inner worm-derived germinal membrane; produces brood capsules and daughter cysts

Key contents:

Brood capsules — small intracystic masses in which scoleces (future worm heads) develop
Daughter cysts — true replicas of the mother cyst
Hydatid sand — freed brood capsules + scoleces floating in hydatid fluid
Scolex contains a rostellum with 20–50 hooklets and 4 suckers

4. Clinical Features

Symptoms (largely asymptomatic until complications occur)

Abdominal pain (most common)
Dyspepsia, vomiting
Urticarial rash, pruritus (hypersensitivity)

Signs

Hepatomegaly (most frequent sign; usually right lobe)
Palpable mass
Jaundice (~8%) — biliary obstruction
Fever (~8%) — secondary infection

Complications

Complication	Details
Rupture into biliary tree	Most common rupture site; → cholangitis, biliary obstruction, jaundice
Bacterial superinfection	Mimics pyogenic abscess (up to 20% of hepatic cases)
Free rupture into peritoneum	→ disseminated echinococcosis, anaphylaxis
Rupture into pleura/bronchi	→ dyspnea, hemoptysis
Rupture into pericardium	Rare but life-threatening
Portal hypertension	Rare
Budd-Chiari syndrome	Rare
Pancreatitis	Rare

Eosinophilia is not a feature unless the cyst ruptures

5. Imaging

Ultrasound (first-line — most widely used)

Fig. Ultrasound of hydatid cyst at varying stages: (A) Simple cyst with hydatid sand. (B) Daughter/granddaughter cysts — typical "rosette" appearance. (C) Amorphous mass filling (can mimic solid lesion). (D) Calcified cyst with "eggshell" appearance. — Sabiston Textbook of Surgery

Gharbi classification (also WHO-IWGE classification) stages cysts from simple unilocular to calcified.

Diagnostic US features:

Well-circumscribed cyst with budding signs on the membrane
Free-floating hyperechoic hydatid sand
Rosette pattern — daughter cysts present
Eggshell calcification — highly suggestive

CT / MRI

CT scan showing hydatid cyst in right lobe of liver

Fig. CT showing typical hydatid cyst in right hepatic lobe. — Sleisenger & Fordtran's Gastrointestinal and Liver Disease

Avascular cysts with ring enhancement
Multiple daughter cysts with intracystic septations
Peripheral focal calcifications
Fluid density varies with proteinaceous debris
Better than US for extrahepatic disease and hepatic anatomic relationships

ERCP / PTC

Indicated when biliary involvement is suspected

Plain X-ray

Ring-like calcifications visible in up to one-fourth of hepatic cysts (E. granulosus)

6. Laboratory / Serology

Test	Details
ELISA	Best serologic test; sensitivity 84–90%
Weinberg reaction	Older complement fixation test; up to 38% false-negative rate
Eosinophilia	Only present if cyst ruptures; otherwise absent
Routine bloods	Usually normal LFTs; leukocytosis if infected
Casoni skin test	Nonspecific; no longer recommended
Cyst fluid analysis	Detection of protoscolices or acid-fast hooklets confirms diagnosis

All serologic tests are plagued by low sensitivity and specificity; imaging is more reliable

7. Gross Pathology

Liver resection specimen showing hydatid cyst with multiple daughter cysts

Fig. Liver resection specimen of hydatid cyst (E. granulosus) with multiple translucent daughter cysts. — Sleisenger & Fordtran's GI and Liver Disease

~75% located in the right lobe of the liver
~75% are solitary
Slow, spherical growth pattern
Degenerating cysts: vacuolation of membranes → calcification of wall (calcification does not always imply the cyst is dead)

8. Treatment

General Principles

Most cysts should be treated
Conservative management is appropriate for small, asymptomatic, densely calcified cysts in elderly patients
Preoperative albendazole is recommended to reduce spillage risk; steroids and epinephrine should be on standby for anaphylaxis

A. Surgery (Gold Standard)

Preparation:

Pack off the abdomen to prevent spillage (anaphylaxis + dissemination risk)
Aspirate through a closed suction system
Flush with scolicidal agent (hypertonic saline is standard)

Surgical options:

Approach	Procedure
Conservative	Unroofing → drainage/evacuation, marsupialization, omentoplasty
Radical	Total pericystectomy, partial hepatectomy (formal resection without entering cyst)
Laparoscopic	Drainage and unroofing; encouraging results in selected cases
Biliary involvement	Suture closure of bile duct communication; major biliary repair; postoperative ERCP

Radical and conservative approaches are equally effective
Recurrence rate: 1–20% (generally ≤5% at experienced centres)
Calcified cysts need not be removed

B. PAIR (Percutaneous Minimally Invasive)

Puncture → Aspiration → Injection (scolicidal agent) → Re-aspiration

Previously contraindicated; now accepted in highly selected patients
Two small RCTs show similar success rates to surgery (both limited by small sample sizes)
Best for uncomplicated cysts; requires concomitant antihelminthic cover

C. Medical Therapy (Antihelminthics)

Drug	Dose
Albendazole (preferred)	10 mg/kg/day in 2 divided doses × 28 days; repeat 3–4 cycles with 2-week breaks between cycles
Mebendazole	Alternative; higher doses required

Effective at shrinking cysts in E. granulosus; complete disappearance in <50%
Used preoperatively to reduce spillage risk
Monotherapy (without drainage/resection) reserved for:
- Widely disseminated disease
- Poor surgical candidates

9. E. multilocularis vs E. granulosus — Key Differences

Feature	E. granulosus (Cystic)	E. multilocularis (Alveolar)
Cyst type	Well-defined fluid-filled cysts	Solid invasive masses
Appearance	Unilocular/multilocular cysts	Alveoli-like microvesicles
Growth pattern	Expansile	Infiltrative ("invasion" of parenchyma)
CT	Calcified cysts, daughter cysts	Scattered calcified necrotic tissue
Mimics	Simple hepatic cyst, abscess	Cirrhosis, hepatocellular carcinoma
Prognosis	Good with treatment	Poor; mortality ~90% without treatment
Surgery	Usually curative	Curative in only ~1/3; often inoperable at diagnosis
Medical	Albendazole effective	Long-term albendazole indefinitely (if inoperable)

10. Key Points Summary

Caused by E. granulosus (most common), a tapeworm whose definitive host is the dog
Humans are accidental intermediate hosts infected via fecally contaminated food
Liver is most commonly affected (70%), followed by lungs (20%)
Cyst wall: pericyst (host) / ectocyst (outer worm) / endocyst (germinal, inner worm)
Largely asymptomatic until complications develop
Most dangerous complication: free rupture → anaphylaxis
Most common rupture site: biliary tree → cholangitis
Ultrasound is the primary imaging tool; rosette sign and eggshell calcification are pathognomonic
ELISA is best serology (84–90% sensitive); Casoni test is obsolete
Treatment: Surgery ± preoperative albendazole is the mainstay; PAIR for selected cases
Hypertonic saline is the standard scolicidal agent used intraoperatively

Sources: Sabiston Textbook of Surgery, p. 1891–1892 | Sleisenger & Fordtran's GI and Liver Disease, p. 1589 | Goldman-Cecil Medicine, p. 1599–1600 | Jawetz Melnick & Adelberg's Medical Microbiology

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