Hepatic hydatid cyst: ultrasound water lily sign
Patient was referred to the Emergency Department for FAST scan after sustaining blunt abdominal trauma. She was otherwise asymptomatic
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There is evidence of a well defined cystic lesion measuring 8.0 cm x 6.5 cm x 7.4 cm in the right lobe of liver (segment VII/VIII) with low-level internal echoes. The cyst shows a detached, irregular laminated membrane inside it which appears to float within the contents of the cyst.
Rest of the study is unremarkable.
Findings are suggestive of hepatic hydatid cyst with ultrasound "water lily sign" ( Stage CE3a).
Hydatid disease is a zoonosis caused by the larval stage of the tapeworm Echinococcus. Human infection is known to be caused by E. granulosus and E.multilocularis.
The hydatid cyst has three layers:
- Pericyst: the outermost layer which is composed of modified host cells forming a dense fibrous coat.
- Middle laminated membrane which is acellular
- Inner germinal layer which produces the scolices and laminated membrane.
The middle and germinal layers form the true cyst wall or the endocyst, although the middle layer is occasionally referred to as the ectocyst.
The water lily sign is classically described in pulmonary hydatid disease on x-ray. However, "floating membranes" in a hydatid cyst can be seen on ultrasound and is referred to as "ultrasound water lily sign." According to the WHO classification of hepatic hydatid cysts, the water-lily sign is seen in stage CE3a, which represents a transitional stage between active and inactive disease. The mechanism of detachment of membrane is related to decreased intra-cystic pressure, degeneration, host response, trauma or following therapy.
- 1. Pedrosa I, Saíz A, Arrazola J et-al. Hydatid disease: radiologic and pathologic features and complications. Radiographics. 20 (3): 795-817.
- 2. Giorgio A, Di Sarno A, de Stefano G et-al. Sonography and clinical outcome of viable hydatid liver cysts treated with double percutaneous aspiration and ethanol injection as first-line therapy: efficacy and long-term follow-up. AJR Am J Roentgenol. 2009;193 (3): W186-92. doi:10.2214/AJR.08.1518