Concomitant Hydatid Disease of the Lower Extremity and Retroperitoneum: A Case Report of Two Rare Locations.

Cystic echinococcosis is an endemic parasitic disease in Morocco, characterized by cystic lesions, most commonly in the liver or lungs, with lesions in other locations being less common. We report the case of a 38-year-old woman presenting with chronic pain and swelling in her left thigh. An ultrasound of the thigh revealed a multilocular mass located on the posteromedial aspect of the thigh. An MRI of the left thigh showed a multilocular subfascial cystic mass containing multiple fluid-filled vesicles and a sinuous hypointense membrane (serpent sign). An MRI of the thoracolumbar spine and an abdominal CT scan revealed additional lesions in the left psoas muscle and the left retroperitoneal space, in close contact with the kidney. Imaging showed no liver or lung lesions. The patient underwent surgery. The pathology report confirmed that the cystic lesions were of hydatid origin. This case underscores the importance of considering hydatid disease when evaluating cystic masses in soft tissues or the retroperitoneum, even in the absence of liver or lung involvement.