Introduction: Hydatid disease is a helminthic anthropozoonosis with worldwide distribution due to the close associations among sheep, dogs, and humans. It can occur almost anywhere in the body with a variety of imaging features, which may change according to the growth stage, associated complications, and affected tissues. A definitive diagnosis requires a combination of imaging, serologic and immunologic studies. Ultrasonography, computed tomography and magnetic resonance imaging are highly accurate in detecting a hepatic hydatid cyst. However, hepatic hydatid cysts in an unusual location and/or of an unusual dimension, with atypical imaging findings, may complicate the differential diagnosis. Surgical treatment remains the best treatment.
Case presentation: We describe an unusual case of a giant hydatid cyst, with exophytic growth from the right lobe of the liver of a 55-year-old Egyptian man. The cyst was strongly adhered to his ipsilateral kidney, which was displaced in a downwards and anterior direction, close to his abdominal wall, simulating a retroperitoneal origin. This atypical growth raised doubts about the most appropriate surgical approach. Magnetic resonance imaging easily clarified the origin of the cyst as our patient's liver, allowing accurate surgical planning.
Conclusion: Rarely, hydatid cysts can reach an extremely large size without any additional symptoms. Giant cysts need radical therapy because they might lead to perforation and anaphylaxis in some patients. Magnetic resonance imaging is very useful in the study of hydatid disease because of its capacity to allow a large field of view, multiplanar acquisition, and high contrast resolution. In some unusual hepatic presentations, magnetic resonance imaging can be used to determine the correct anatomical relationships.