Water lily sign (hydatid cyst)

Last revised by Yoshi Yu on 29 May 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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