The incidence of cardiac involvement among patients with hydatid disease is 0.5-3%, and a pericardial site of implantation is even less common . A mediastinal site for the disease is also rare compared with a pulmonary location .

Pericardial involvement in hydatid disease is rare and frequently occurs as a result of rupture of a primitive hydatid lesion, the location of which is almost exclusively cardiac . Intrapericardial rupture of a cyst can lead to pericarditis  effusion, and cardiac tamponade, which can be fatal (22.5% of cases of intrapericardial rupture). The cause is not so much the hydatid fluid contained in a large cyst but an exaggerated exudative reaction of the serous membrane of the pericardium. Pericardial HCs are generally located in the right costophrenic recess; however, unusual locations such as the left costophrenic recess, the hila, and the superior mediastinum at the level of the aortic arch may also be encountered. Pericardial HCs produce deformation of the lung contours at chest radiography.

Signs and symptoms of cardiac hydatid cysts are extremely variable and directly related to the location and the size of the cysts. Only approximately 10% of patients, especially those with large hydatid cysts, have clinical manifestations. Precordial pain is the most common symptom and is most often vague and does not resemble angina pectoris. Precordial pain also can be of the pericardial type, especially in patients with a pericardial hydatid cyst and a pericardial reaction

As with cardiac hydatid disease, CT is of limited value in the evaluation of pericardial hydatid cysts due to motion artifact. However, adequate contrast material filling within the cardiac chambers can provide important information about the location and internal structure of the lesion.

Contrast-enhanced CT shows  the presence of a well-defined, thin-walled, homogeneous cystic mass with internal trabeculae.

Hydatid cysts  are classified into four types on the basis of their appearance

Type I HCs appear as a well-defined anechoic mass with or without hydatid sand and septa. Unilocular cysts are considered to be an initial stage in the development of the parasite .

 

Daughter cysts are seen inside the mother cyst. Floating membranes or vesicles can also be seen in the cyst . Sometimes multiple cysts and echogenic areas that are enclosed together within a single capsule give rise to a “racemose” or wheel spoke” appearance. Consolidation of the daughter cysts may produce echogenic solid lesions.

At CT, type II HCs can be visualized in three stages depending on the age, number, and arrangement of the daughter cysts .

 Type IIA lesions contain round daughter cysts arranged at the periphery . The average CT attenuation of the mother cyst is higher than that of daughter cysts.

Type IIB lesions contain larger, irregularly shaped daughter cysts that occupy almost the entire volume of the mother cyst. The high-attenuation fluid that surrounds the daughter cysts within the mother cyst looks like septa, creating a “rosette” appearance .

Type IIC lesions appear at CT as relatively high-attenuation round or oval masses with scattered calcifications and occasional daughter cysts. These findings represent the degeneration of old cyst with amorphous and tenacious content.

Type III: Calcified Cyst
Type III lesions are dead cysts with total calcification. They demonstrate strong posterior shadowing at ultrasonography (US) and manifest as round, hyperattenuating areas at CT and hypointense areas at MR imaging.

Hydatid cysts complications include rupture and superinfection and may be seen in both type I and type II HCs. Rupture occurs in 50%–90% of cases. Cyst rupture is mainly due to the degeneration of parasitic membranes as a result of age, chemical reactions, or a host defense mechanism . HC rupture may be contained, communicating, or direct. In contained rupture, undulating membrane resulting from separation of the endocyst from the pericyst is seen at both US and CT and manifests as postural changes. A “snowstorm” pattern has been described at US. The infected HC may exhibit mixed echogenicity.

Bacterial superinfection of HC is always secondary to rupture. Up to 25% of ruptured cysts may become infected. Numerous signs of cyst infection have been described, including poor delimitation, mixed internal echoes, and air-fluid or fluid-fluid levels.