Hydatid disease

Last revised by Tariq Walizai on 5 Dec 2024

Hydatid cyst, also known as echinococcosis, results from infection by the Echinococcus tapeworm species. It primarily includes two significant zoonotic diseases caused by tapeworms: cystic echinococcosis, resulting from Echinococcus granulosus, and alveolar echinococcosis, resulting from Echinococcus alveolaris/multilocularis 1,2.

The prevalence and primary endemic regions of alveolar echinococcosis and cystic echinococcosis differ:

  • cystic echinococcosis is more common and has a worldwide geographical distribution. Highly endemic areas for cystic echinococcosis include western China, Central Asia, South America, Mediterranean countries, and East Africa6,12.

  • alveolar echinococcosis is less common than cystic echinococcosis and is predominantly endemic in the northern hemisphere, particularly in North America, west-central Europe, the Near East, Siberia, Central Asia, Japan, and China12.

Echinococcosis is caused by the larvae of tapeworms (cestodes) of the genus Echinococcus (family Taeniidae).

The primary host is the dog or wolf for Echinococcus granulosus and the fox for Echinococcus alveolaris/multilocularis.

Echinococcosis in humans is primarily caused by the accidental ingestion of Echinococcus larvae. Humans act as incidental hosts3.

mediastinal hydatid infection (very rare) 9

The cysts usually have three components 1,2,10,11:

  • pericyst: dense fibrous capsule produced by the host

  • exocyst (laminated membrane): semi-permeable acellular mucin-based membrane produced by the parasite

  • endocyst: germinal layer of the parasite, which produces daughter cysts containing protoscolices (larval parasite) on its internal surface and laminated membrane on its outer surface

Based on morphology the cyst can be classified into four different types 2:

  • type I: simple cyst with no internal architecture

  • type II: cyst with daughter cyst(s) and matrix

    • type IIa: round daughter cysts at the periphery

    • type IIb: larger, irregularly shaped daughter cysts occupying almost the entire volume of the mother cyst

    • type IIc: oval masses with scattered calcifications and occasional daughter cysts

  • type III: calcified cyst (dead cyst)

  • type IV: complicated cyst, e.g. ruptured cyst

A chest film or other plain films can be the first diagnostic modality when echinococcosis is suspected, depending on clinical indications. 

Ultrasound is commonly used to classify hepatic hydatid disease using either the Gharbi classification 4 or the WHO-IWGE classification.

CT and MRI imaging are indicated when considering surgical treatment, particularly in regions like the brain, spine, and locations inaccessible for conventional radiography or ultrasound, or in case of diagnostic uncertainty.

The Gharbi ultrasound classification consists of five stages 4:

  • stage 1: homogeneously hypoechogenic cystic thin-walled lesion 

  • stage 2: septated cystic lesion 

  • stage 3: cystic lesion with daughter lesions

  • stage 4: pseudo-tumor lesion 

  • stage 5: calcified or partially calcified lesion (inactive cyst)

Four treatment options are available 7:

  • surgical excision

  • PAIR (puncture, aspiration, injection of protoscolicidal agent and reaspiration)

  • chemotherapy with an anti-helminthic agent (albendazole, mebendazole)

  • watch and wait for inactive and silent cysts

Treatment outcomes were improved when surgery or PAIR was combined with benzimidazole given before and after surgery 7. Regarding medical management, higher scolicidal and anti-cystic activity was seen in combination therapy with albendazole plus praziquantel and was more likely to result in cure or improvement 7.

Cases and figures

  • Figure 1: echinococcus life cycle
  • Figure 2: microscopy-echinococcus granulosus scolex
  • Figure 3: Water lily image
  • Figure 4: photograph - hydatid cyst membrane
  • Figure 5: stages in liver
  • Figure 6: pleural hydatid cysts
  • Figure 7: hydatid disease
  • Figure 8: serpent (illustration)
  • Figure 9: pathology photograph
  • Case 1: retroperitoneal hydatid
  • Case 2: hepatic hydatid
  • Case 3: pulmonary and hepatic hydatid
  • Case 4: intracranial hydatid cyst
  • Case 5: splenic hydatid cyst
  • Case 6: intracranial hydatid cysts
  • Case 7: pulmonary hydatid cyst
  • Case 8: peritoneal hydatid cyst
  • Case 9
  • Case 10: renal
  • Case 11: hepatic, splenic and pulmonary hydatid cysts
  • Case 12
  • Case 13
  • Case 14: pelvic
  • Case 15
  • Case 16: in the neck
  • Case 17: ruptured splenic hydatid cyst
  • Case 18: multiple hepatic and pulmonary hydatid cysts
  • Case 19: lung, liver and pericardial hydatid
  • Case 20: intramuscular
  • Case 21: pelvic hydatid cyst
  • Case 22: hepatic, intra and retro peritoneal
  • Case 23: peritoneal spread
  • Case 24: disseminated hydatid disease
  • Case 25
  • Case 26
  • Case 27
  • Case 28
  • Case 29
  • Case 30
  • Case 31: type I- simple cyst
  • Case 32: hepatic and pelvic hydatid cysts
  • Case 33: thoracoabdominal hydatid cysts
  • Case 34: hepatic hydatid cyst
  • Case 35: hepatic hydatid cyst
  • Case 36
  • Case 37
  • Case 38
  • Case 39: renal
  • Case 40: hepatic
  • Case 41: renal ultrasound
  • Case 42: splenic
  • Case 43: hepatic hydatid cysts with cystobiliary communication
  • Case 44: posterior fossa hydatid cyst
  • Case 45: Extra-foraminal

Imaging differential diagnosis

  • Giant splenic pseudocyst
  • Ovarian cyst - prepubertal
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