Imaging findings in hydatid disease range from purely cystic lesions to solid-appearing masses. Ringlike or total calcifications, common in the liver, spleen and kidneys, often signify natural disease evolution. A highly specific feature is the detachment of the endocyst from the pericyst, forming 'floating membranes' within the cavity. Sonography may reveal the 'water lily sign' indicating complete membrane detachment at air fluid interface. Multivesicular cysts present as well-defined, honeycomb-patterned, with septa representing daughter cyst walls. When daughter cysts are surrounded by the mixed echogenic hydatid matrix, a characteristic 'wheel spoke' pattern emerges.

CT imaging provides a comprehensive view, identifying the extent of disease, with hallmark signs like the water lily sign and meniscus sign. MRI, especially valuable in complex cases involving the CNS and renal systems, highlights T2 hypointense membranes and neural involvement with superior detail. These imaging characteristics are crucial in differentiating hydatid disease from other neoplastic lesions, facilitating timely and accurate diagnosis.

Intraperitoneal & Retroperitoneal hydatid disease  accounts for 13% of all abdominal hydatidosis. These cysts typically arise secondary to the spontaneous or iatrogenic rupture of hepatic, splenic, or mesenteric cysts and can occur anywhere within the peritoneum. Primary peritoneal involvement is extremely rare. Single, unilocular peritoneal hydatid cysts are often indistinguishable from other peritoneal cysts, such as mesenteric or duplication cysts, based solely on imaging. Isolated retroperitoneal HD is also rare and usually results from secondary liver involvement.

Splenic hydatid disease is rare, comprising 0.9%–8% of cases and  third common site after liver and lung involvement. Primary splenic hydatidosis (<2%) arises from systemic dissemination or rupture of liver cysts. Typically solitary, splenic cysts exhibit classical hydatid imaging features. Differentials include epidermoid cysts, pseudocysts, abscesses, hematomas and neoplasms.

Genitourinary hydatid disease is rare, with kidney involvement in 3% of cases, typically as unilateral cysts in the poles. About 18% of renal cysts rupture into the collecting system, causing hydatiduria. Imaging reveals unilocular or multiloculated cysts with daughter cysts and occasional mural calcifications. Differentials include simple cysts, abscesses, and necrotic neoplasms.

Musculoskeletal hydatidosis is also very rare, due to its low incidence and nonspecific clinical manifestations, the diagnosis of musculoskeletal hydatidosis can be challenging. Radiologically, bone hydatid cysts can mimic tumors and inflammatory conditions, including osteomyelitis, with erosive and destructive changes in bone.

Pulmonary hydatid- Lungs are the second most frequent site of hematogenous spread in adults. While calcification in pulmonary cysts is rare, it can occasionally be seen in pericardial, pleural and mediastinal cysts. Intrapulmonary cysts may cause erosion in the bronchioles, leading to the introduction of air between the pericyst and its laminated membrane. This air collection appears as a thin, radiolucent crescent in the upper part of the cyst, known as the crescent or meniscus sign. 

Sign of complete rupture  in Pulmonary hydatid disease  is Onion peel sign (Cumbo, double arch sign )  that shows  curvilinear membrane outlined by air both inside the endocyst and a crescent of air between the endocyst and pericyst.

Spinal hydatid- Spinal hydatid cysts account for 1% of all cases of hydatid disease, with osseous involvement seen in 0.5% to 2% of cases, approximately half of which are vertebral. Among vertebral involvements, 50% are in the thoracic region, 20% in the lumbar area, while sacral and pelvic involvement is rare. Spinal extradural hydatid cysts are extremely rare. The disease typically spreads to the spine through direct extension from pulmonary, abdominal, or pelvic infestations, most commonly affecting the dorsal region of the spine.