In pulmonary hydatid disease, the radiologial signs are usually precise contrary to the clinical presentation. The appearance of a pulmonary hydatid cyst may change secondary to perforation which necessitates further use of CT. Endocyst detachment associated with rupture is seen as a floating membrane within the cyst by CT. Characteristically, the crumpled endocyst membranes floating freely on the surface of the remaining cyst fluid after the complete collapse results in a convex serpinginous margin at the air-fluid level, an apearance known as ***water lily sign*** or ***floating lily sign***.

http://www.dograrad.com/?thecategory=11&p=438

Kyste univésiculaire qui peut contenir des vésicules filles
Contenu anéchogène avec détachement d’une membrane laminée de la paroi du kyste visible comme membrane
flottante ou comme ***'water-lily sign’*** qui est indicatif des membranes flottantes en dessus des débris du liquide
kystique.
Forme du kyste moins ronde à cause de la réduction de la pression intra kystique

http://www.sante.gov.ma/Departements/DELM/Maladies Parasitai...

It is only a suggestion and it is also true that my references are all to the pulmonary hydatid disease (most of the Google results to this search are related to it) but I think you will lose the image suggested by 'nénuphar' if you choose only 'floating'. Good luck.

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