Echinococcal disease is usually caused by a tape-worm, Echinococcus
granulosus. Humans are a secondary host who get infected by ingesting
is the most commonly affected organ, although the lungs, spleen,
bones, kidneys, and central nervous system can also be affected.
The sonographic appearance of hydatid cysts depends tip on the
stage of evolution and maturity and the presence or absence of
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.
The differential diagnosis of hydatid disease of the liver includes
* Necrotic hepatic metastases.
* Liver abscesses.
* Polycystic kidney disease.
* Epidermoid cyst
* Bile duct cysts.
* Caroli's disease.
the most widely used being the one proposed
by Gharbi (Tunisia) in the early 1980s
(Click on the image below)
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
Hydatid cyst of the adrenal
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
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.