Water lily sign (hydatid cyst)

Last revised by Rohit Sharma on 5 Dec 2024

The water lily sign, also known as the camalote sign, is seen in hydatid infections when the inner endocyst detaches from the outer pericyst, resulting in a free-floating membrane within the cyst.

It is classically described on plain radiographs (mainly chest x-ray) when the collapsed membranes are calcified, but may be seen on ultrasound, CT, and MRI.

History and etymology

The water lily sign is termed for its resemblance to a water lily pad floating on water 5. Similarly, camalote is another name for the water hyacinth, a free-floating aquatic plant 6.

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