At the Viewbox: Hydatid Cyst of the Lung

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Hydatid Cyst of the Lung

A 12-year-old girl presented with cough and fever. PA chest X-ray shows a large air filled cyst in the left lung base (A). Contrast enhanced axial CT image (B) demonstrates a round cyst with air-fluid level and detached-floating germinative membranes (asterisk), which are typical for hydatid disease.


Echinococcosis or hydatid disease is a parasitosis caused by infestation with Echinococcus granulosus (dog tapeworm). Although most children with pulmonary involvement by hydatid disease are asymptomatic, they may occasionally present with fever, shortness of breath, cough, and/or chest pain, which is usually a sign of cyst rupture. Diagnosis of hydatid disease depends on the combination of imaging findings and serology tests that use antigens specific for the organism.

The radiological findings are characterized by single or multiple (~25%), round or oval-shaped, cystic nodules or masses (1-20 cm in diameter) with well-defined walls, surrounded by normal lung parenchyma. Other findings include an air-crescent sign when a cyst communicates with a bronchus or the “water-lily sign” when a cyst membrane floats in residual fluid after the rupture of cyst. The water-lily sign is considered to be highly specific or pathognomonic, especially in endemic areas.

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Yikilmaz A.  At the Viewbox: Hydatid Cyst of the Lung.  J Am Osteopath Coll Radiol.  2014;3(2):36.

By Ali Yikilmaz, M.D.| December 02, 2015

About the Author

Ali Yikilmaz, M.D.

Ali Yikilmaz, M.D.

Dr. Yikilmaz works with Istanbul Medeniyet University, Goztepe Research and Training Hospital, Department of Radiology, Istanbul, Turkey.


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