Hydatid disease is caused by Echinococcus granulosus; humans are intermediate hosts, dogs and ships being definitive and intermediate hosts respectively. Infection occurs through contact with a definitive host or intake of contaminated food or water; the liver is the organ mainly involved (1).
Peritoneal echinococcosis is an infrequent condition. It is almost always secondary to a hepatic hydatid disease, which is a complication in 13% of cases, whereas primary peritoneal echinococcosis is rather rare (1, 2). Mechanism of primary peritoneal seeding remains unclear. Contamination of the peritoneal cavity is due to a spontaneous rupture of an echinococcal hepatic cyst in up to 12% of patients but in most of cases it is secondary to an intraoperative spillage of the hydatid fluid during surgery for a hepatic disease. In few cases asymptomatic micro-rupture of a hepatic hydatid cyst, whether spontaneous or post-traumatic, is advocated as a possible pathologic mechanism of peritoneal seeding (1, 2).
Peritoneal echinococcosis usually remains asymptomatic until cysts become large enough to produce a mass effect (1, 2). Cysts can be isolated or multiple, and may implant everywhere in the abdominal cavity; they can show different imaging patterns according to the own evolutive stage (Fig. 5).
Cysts occupying the whole peritoneal cavity may mimic a multiloculated mass, a condition known as encysted peritoneal hydatidosis (1).
Spontaneous rupture of a hydatid cyst within a hollow viscus is a very rare complication with an estimated incidence of 0.5% of cases (1); it can clinically present with hydatidemesis or hydatidorrhea with regard to the perforation site (1-3).
An echinococcal cyst-enteric rupture is usually diagnosed during surgery, although it seldom may be suspected in pre-surgical radiologic work up (1-3). Ultrasonography is the first-level method for identifying and classifying a hydatid cyst (4), but CT is the method of choice for detecting and diagnosing an abdominal echinococcosis, whose appearance resemble findings of hepatic disease (1-5). Some hydatid cyst may characteristically show a hyperattenuating rim on non-enhanced CT scan: this finding is not wholly elucidated, but it may depend on tiny calcium deposit or pericystic fibrotic reaction (6).
Rupture within a hollow viscus can be established when CT detects an air-fluid level within an abdominal cyst. Scans in lateral decubitus can aid in the diagnosis as filling or emptying of the cystic cavity can be demonstrated; the communication between the cyst and the hollow viscus can be seldom demonstrated with CT scans obtained with the contrast medium administered orally or by enema (1).