Role of interventional radiology in the management of hepatic hydatid disease

Table 1 World Health Organization classification of hydatid cyst, highlighting its imaging features[12,13]

WHO classification	Stage	Features
CL	Active	Unilocular cystic lesion without a well-defined wall (double wall sign is not seen); no internal debris or septations (without evident signs of non-parasitic aetiology); seen during the initial phase of hydatid development; requires diagnostic tests to differentiate from other cystic lesions
CE1	Active	Unilocular cystic lesion with a well-defined wall; fine internal echoes/debris may be seen representing hydatid sand (pathognomonic): “Snowflake sign”; “double wall sign” (pathognomonic): Two echogenic lines seen representing the parasite larval cyst and the host-derived fibrous cyst capsule, separated by minimal hypoechoic fluid. However, may not always be seen, and care should be taken not to dismiss a CE1 cyst on the basis of not seeing this sign; internal septae/membranes not seen
CE2	Active	Multivesicular cystic structure with daughter vesicles; rosette/Honey-comb pattern: Daughter cysts fill the entire mother cyst; spoke-wheel pattern: Daughter vesicles arranged peripherally with minimal central high-density matrix
CE3a	Transitional	Detachment of endocyst from pericyst: Can be due to decreasing intracystic pressure, degeneration, host response, trauma, or response to therapy: Produces serpentine linear floating membranes: “Water-lily sign” (highly specific sign); detachment may be partial or complete
CE3b	Transitional	Few daughter cysts in a predominantly avascular solid matrix: “Swiss cheese” because of significant solid component it can mimic malignancy
CE4	Inactive	Heteroechoic solid avascular mass with no daughter cysts: Pseudotumour/ball-of-wool/canalicular/cerebroid appearance; due to solid nature: Mimics malignancy (requires contrast-enhanced CT/MRI: Showing lack of enhancement to differentiate from malignancy)
CE5	Inactive	Thick, densely calcified walls (complete or near complete); partial wall calcification does not always indicate parasite death; however, densely calcified cysts may be assumed to be inactive; wall calcification is most extensively found in, but not limited to CE4 and CE5; heterogeneous avascular solid content (when acoustic shadow allows visualization)

WHO: World health organization; CL: Cystic lesions; CE: Cystic echinococcosis; CT: Computed tomography; MRI: Magnetic resonance imaging.