Hydatid cyst

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Echinococcal disease is usually caused by a tape-worm, Echinococcus granulosus. Humans are a secondary host who get infected by ingesting egg-infested vegetables.
The liver is the most commonly affected organ, although the lungs, spleen, bones, kidneys, and central nervous system can also be affected.

Sonography :
The sonographic appearance of hydatid cysts depends tip on the stage of evolution and maturity and the presence or absence of complications.
The hydatid cyst can be slow-growing and asymptomatic and may be single or multiple, depending on the degree of infestation.
Although the appearances are often similar to those of a simple cyst, the diagnosis can be made by looking carefully at the wall and contents : the hydatid cyst has two layers to its capsule, which may appear thickened, separated or detached on ultrasound. Daughter cysts may arise from the inner capsule the honeycomb or cartwheel appearance. A calcified rind around a cyst is usually associated with an old, inactive hydatid lesion.
The presence of a heterogeneous mass with areas of increased and decreased echogenicity may represent a secondary infection of the cyst. In these circumstances ultrasound diagnosis of a hydatid cyst is not always possible. The presence of air within the lesion may make the mass very echogenic. Solid cysts may occur demonstrating the 'ball of wool' sign ,'spin' sign, 'whorl' sign or 'congealed waterlilly' sign. A 'spin' or 'whorl' sign representing collapsed parasitic membranes is considered strong evidence of hydatid disease even in the presence of negative serology.
The presence of a fat-fluid level in a hepatic hydatid cyst may be a sign of rupture into the biliary tree. With rupture into the biliary tree the contents of the cyst may become echogenic with or without posterior acoustic enhancement with a wall defect communicating with a biliary radical. The common bile duct may be dilated with echogenic material.

Management of hepatic hydatid cysts has traditionally been surgical resection. However, recently percutaneous drainage under ultrasound guidance, with or without medical therapy, bas been advocated. At the present stage of knowledge surgery remains the treatment of choice perhaps supplemented by medical therapy.

Differential :
The differential diagnosis of hydatid disease of the liver includes
* Necrotic hepatic metastases.
* Liver abscesses.
* Hematomas.
* Polycystic kidney disease.
* Epidermoid cyst
* Bile duct cysts.
* Caroli's disease.
* Amebiasis.

Classification :
the most widely used being the one proposed by Gharbi (Tunisia) in the early 1980s
(Click on the image below)

Type I

II

III

IV
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V
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Splenic hydatid cyst
In endemic areas the spleen is involved in 5 % of cases and it is about twice as common as other benign cysts. The cysts tend to have a fairly well defined wall and are usually multiloculate. However they may be unilocular which may resemble a simple cyst, caution is therefore required in endemic areas. Splenic hydatid cysts may calcify.

Renal hydatid disease
Granulosus infection usually bas a cystic appearance, which initially is similar to a simple cyst but becomes more complex with time developing an endocyst and membranes. Separation of endocyst may give rise to the 'floating lily' sign of floating septae. As with the liver, renal hydatid cysts may be multiloculate, complex or solid. Cyst-wall calcification results in a densely echogenic shadowing mass.

Hydatid cyst of the adrenal gland
Hydatid cysts of the adrenal gland are rare and represent 7 % of all adrenal cysts whilst the adrenal gland is involved in 0.5 % of all Ecbinococcus granulosis infections. The ultrasound features depend upon the stage of evolution of disease. Early lesions appear purely cystic and unilocular, indistinguishable from other benign cysts. Eventually the capsule become fibrotic and some may calcify. The discharge of daughter cysts from the wall gives it a multilocular appearance.

Primary pelvic hydatid
cyst A pelvic hydatid cyst is rare and usually presents with pressure symptoms involving adjacent organs (bladder , sigmoid and rectum). It may present with obstructive uropathy leading to renal failure. Ultrasound appearances are those of a multiloculated cyst.