Teaching Case

A 73-year old man was hospitalized after experiencing fever, right upper quadrant pain and jaundice, attributed to cholangitis. He subsequently developed signs of peritonitis.

The patient was hospitalized due to an episode of cholangitis. He had a history of choledocholithiasis and had been submitted to ERCP/papillotomy, 3 years before. Despite medication the patient developed sepsis, with signs of acute abdomen. He could not recall recent trauma. A CT scan showed a 9 cm hydatid cyst with eggshell calcification, with its upper part in liver segment IV, while its lower part was exophytic (Fig. 1a-k). Fluid content, as well as air bubbles were evident inside the lesion. Fluid and air bubbles were also apparent between the lesion and the adjacent stomach, duodenum, pancreas and inferior vena cava. The calcified wall of the cyst had multiple discontinuations. The air bubbles could be attributed to either an infection of the hydatid cyst or a fistulous communication with the GI tract. The latter was excluded, as the patient never had an episode of hydatidemesis. There was also hypodense cuffing around the portal triads consistent with periportal oedema, with probable coexisting distension of the intrahepatic bile ducts (masked within the periportal cuffing). This could be due to mass effect from the lesion at the porta hepatis, blocking lymph and bile drainage. The differential diagnosis could also include a concomitant intrabiliary hydatid rupture. The patient was shortly after operated. Surgery revealed an inflamed hydatid cyst containing purulent and hemorrhagic fluid, which had ruptured into the adjacent tissues. No bile content was found in the fluid after biochemical control. No fistulous communication between the cyst and the GI tract was detected.

Hydatid disease is a zoonosis caused by the Echinococcus tapeworm, either granulosus or multilocularis. Ecchinococcus granulosus is endemic in sheep farming regions (e.g. Mediterranean).
Humans are intermediate hosts, infected by contact with dogs/sheep, or ingestion of contaminated water/vegetables. The parasite passes through the intestine, reaching portal venous/lymphatic system, with the liver most frequently involved (75%), mainly its right lobe. Liver cysts grow to 1cm in the first 6 months and 2–3cm/year later.
The hydatid cyst has three layers: a.) the outer pericyst (host cells forming a dense fibrous zone), b.) the middle laminated membrane (acellular, allowing nutrient passage), c.) the inner germinal layer (producing scolices and the laminated membrane). Cyst fluid is clear.
Imaging findings depend on growth stage: starting from fluid-filled, cyst-like (Type I), to Type II, with daughter cysts and/or matrix. Type II lesions may die becoming calcified Type III lesion. A curvilinear/ringlike calcification pattern, representing calcified pericyst is seen in 20–30% at radiography. Partial calcification does not mean parasite death, but densely calcified cysts are considered inactive. The pericyst tends to be hyperdense on CT. It is hypointense on MR, due to collagen content.
Rupture is usually seen with Type I, II lesions: It may be spontaneous or after trauma. Rupture risk is increased with increased cyst size. There are 3 rupture types: 1.) Contained, meaning ruptured endocyst and intact pericyst. It is clinically silent and seen at cross-sectional imaging as intracystic floating membranes. 2.) Communicating with passage of cyst contents into biliary radicles, incorporated into the pericyst. This may cause biliary obstruction and cyst infection. 3.) Direct (1.75-8.6%) occurring when both pericyst/endocyst rupture, allowing free peritoneal spillage of hydatid material. It is more frequent in lesions near the liver edge, due to deficient pericyst. Direct rupture may result in anaphylaxis, chemical peritonitis, hydatid dissemination and bacterial infection of the pericyst cavity. Infection (5–8%) occurs only after rupture of both pericyst/endocyst (communicating, direct rupture), allowing bacteria to pass into the cyst, with US /CT findings similar to hepatic abscesses. At US the lesion demonstrates poorly defined margins, but may remain well defined, with mixed internal echo-pattern (solid/fluid elements), and air or air-fluid levels. CT is the modality of choice for demonstrating infection, with infected cysts manifesting as poorly defined masses, in contrast to the clearly defined uncomplicated cysts. CE-CT may reveal the typical high-attenuation rim, surrounding the lesion. Occasionally, patchy areas of contrast-enhanced liver parenchyma are seen in the vicinity of the lesion representing inflammatory changes. CT also depicts most clearly gas or air-fluid levels within the cyst. Surgery is the treatment of choice for perforated hydatid cysts. However, the best approach has not been clearly defined. Radical procedures for patients in need of an urgent operation may not be feasible and more conservative approaches reserved for such cases. Intraperitoneal rupture and infection of a hydatid cyst are rare complications of hydatid disease but must be considered in the differential for patients with acute abdomen, living in the endemic zone.