Echinococcal cysts are mostly found in the liver (75%) and lungs (15%); less frequently they involve anatomical locations such as the brain, bones and heart .
The clinical manifestations of hepatic HD depend on the site, size and stage of development of the cyst  and HD is largely asymptomatic until complications occur . Uncomplicated liver cysts are always initially asymptomatic, especially when they are small, well-encapsulated or calcified cysts. Rupture of the cyst because of trauma or hyper-pressure from the growing cyst are the most common complications, and may cause anaphylactic shock or the formation of secondary echinococcosis .
It has been reported that hepatic hydatid cysts grow one centimeter in diameter during the first six months and then two to three centimeters annually; this is strictly related to the surrounding tissue resistance . GHCs are extremely rare and, in advanced disease, complications are common [8, 9].
Typical radiological findings are well known and very helpful in the diagnosis of the disease. US, CT and MRI are highly accurate in detecting hepatic HD [10, 11], and several classification schemes based on cyst appearance have been proposed [1, 12]. US is the first diagnostic technique for hepatic HD and no further imaging techniques are requested when the appearance is typical .
CT and MRI may display the same findings as US; however, calcification of the cyst wall or internal septa is easily detected with CT. It is widely accepted that abdominal CT, with its higher rate of accuracy, is the diagnostic tool of choice. However, MRI, due to its multiplanar capabilities and the excellent contrast resolution for soft tissues, has a particular importance if the diagnosis of HD is questionable, because it is more accurate in demonstrating parietal features and defining anatomical relationships.
Furthermore, hepatic HD may have a low-signal intensity rim on T2-weighted MR images, which probably represents the outer layer (pericyst), rich in collagen and generated by the host. It has been proposed as a characteristic but nonspecific sign  when comparing these lesions with nonparasitic epithelial cysts.
The treatment options for hydatid cyst of the liver depend on stage, localization, size and complications of the cysts, and include nonoperative and operative methods . Operative methods include classical surgical techniques (total or subtotal cyst-pericystectomy, partial hepatectomy, capsulorrhaphy, capitonnage, omentoplasty); minimally invasive techniques, such as laparoscopic or robotic procedures; and other treatment modalities, such as puncture, aspiration, injection and reaspiration of scolicidal solutions. When used alone, chemotherapy with antihelmintics of the benzimidazole family has limited efficacy, mostly related to the accessibility of the cyst to the drug. This treatment outcome is better when used as an adjunct to surgery to prevent recurrence . Indications for surgery are the following: active cyst, complicated cyst (infection, compression and obstruction), cyst located near vital organs (central nervous system, spinal cord and heart) and giant cyst at risk of rupture in pleural and/or abdominal cavities. Radical surgical resection remains the mainstay of curative treatment and an accurate preoperative localization is essential [16, 17]. In our experience, regulated liver resections (major hepatectomy or segmental resection) instead of total or subtotal cyst-pericystectomy are preferable because of a reduced risk of disease recurrence, intraoperative contamination and postoperative complications (biliary fistula, abdominal collection and bleeding). As a consequence, patients with giant hepatic HD should be referred to high volume hepatobiliary centers. Furthermore, it is important to highlight that GHCs usually do not infiltrate adjacent organs but have strong inflammatory adhesions, which allows the surgeon to avoid multiorgan resections.
In our case, the large dimension and proximity to vital organs induced us to operate so as to avoid cystic complications, such as a rupture in the pleural cavity through the diaphragm or inferior vena cava compression. Moreover, the challenge of this case lay in the conspicuity of the HD. Indeed, the hepatic cyst reported here was an extremely rare large asymptomatic cyst originating from the right lobe of our patient’s liver, was well-encapsulated, was not calcified, had a unique retroperitoneal growth, and was strongly adhered to his right kidney, peritoneum and diaphragm, thus suggesting a retroperitoneal origin of the mass.
Hepatic HD may use two common routes of exophytic growth: the bare area of the liver and the gastrohepatic ligament. Growth through the bare area leads to involvement of the diaphragm and extension into the thorax; growth through the gastrohepatic ligament appears to be the path by which the cyst reaches the stomach. In our case, the giant size of the mass created doubt about its origin - hepatic or retroperitoneal. This was because the cyst rotated and displaced his right kidney down and anteriorly, simulating the growth of a retroperitoneal mass.
In this case, multiplanar MRI was the best imaging technique to demonstrate exophytic cyst growth and its migration toward the retroperitoneum and diaphragm, and allowed accurate presurgical diagnosis and surgical planning (that is, the surgical approach: anterior/bisubcostal laparotomy, lombotomy thoracophrenolaparotomy). For these reasons, we believe that MRI is mandatory in the case of a complex hydatid cyst.