In Portugal,
mainly in the southern region of Alentejo,
hydatid disease is still an endemic condition despite public health efforts.
The estimated incidence of human hydatidosis in the Portuguese territory is 2,2 cases per 100 000 habitants/year.
The most common site of involvement is the liver (50 to 70%),
by the larva of the tapeworm Echinococcus granulosus although secondary involvement due to haematogenous spread may be seen in virtually any anatomic location.
Echinococcal cysts are formed by an outer layer of host tissue,
the pericist,
and an inner layer composed of parasite material,
the endocist,
that comprises an outer acellular lamina and an inner germinative layer.
The WHO standardized classification of Echinococcus granulosus ultrasonographic images follows the first classification defined by Gharbi et al.,
and comprises,
within the normal development course of the parasite,
an initial undifferentiated cystic lesion (CL) stage (unilocular,
simple cyst,
without visible wall),
followed by the cystic echinococcosis (CE) stage 1 (unilocular,
sometimes non-pure fertile cyst,
with internal hydatid sand and a visible wall),
2 (multilocular fertile cyst),
3 (transitional degenerative cyst,
with heterogeneous content and detached laminated membrane from the cyst wall),
4 (solid content heterogeneous inactive cyst) and 5 (inactive thick calcified wall cyst).
The two major complications of hepatic hydatid disease are rupture and infection,
being the former the most frequent.
Rupture of the cyst occurs when a discontinuity develops in one or both of the layers described,
and can be classified into three forms: contained,
communicating (divided by two subtypes: small fissures versus wide communications) and direct.
Infection is presumed to only develop when superimposed to a previous communicating or direct rupture.
A ruptured hydatid cyst is the most frequent complication of hepatic hydatidosis and it is rarely assimptomatic.
The most common rupture location is intrabiliary with a reported mortality as high as 50%.
Cyst to biliary tree communication occur due to the incorporation of biliary structures by the pericyst as the cyst expands.
Ultrasonography (US) and Computed Tomography (C.T.) are the gold standard imaging techniques regarding hydatid cyst.
US as long been successfully used as a cost effective means of diagnosing hydatidosis.
The above mentioned imaging modalities are also sensitive and specific for hydatid cyst biliary rupture characterization,
by means of identifying the cyst,
intrabiliary hydatid components and detecting the point of cyst to biliary tract communication.
Most small communicating ruptures are beyond the diagnostic scope of imaging techniques and can be commonly identified by means of endoscopic retrogade cholangiopancreatography (E.R.C.P.).
Also,
subsequent complications due to small fissures (biliary obstruction or odditis) can be better visualized by E.R.C.P.
The diagnosis potential of E.R.C.P.
is complemented by its therapeutic value in decompressing the biliary tree and preventing relapsing obstructive jaundice by endoscopic sphincterotomy.
Familiarity with hydatid disease radiologic findings is crucial in establishing an accurate diagnosis.