Teaching Case

A 56-year-old woman with history of HIV infection and asymptomatic hepatic hydatid cyst came to the emergency room with fever, sweating and right upper quadrant pain that increased with inspiration for fifteen days.

The initial non-enhanced CT study prior to onset of symptoms [Fig. 1] showed a round heterogeneous hypodense mass located in liver segments VII and VIII with foci of calcification in relation to the known history of hydatid cyst.

The emergency chest X-ray [Fig. 2] shows a right subphrenic curvilinear calcified image with air-fluid level within.
As a consequence of the X-ray findings, an abdominal CT was performed [Fig. 3] showing a rounded mass with ill-defined and partially calcified walls and multiple calcified membranes inside. There were air bubbles inside forming an air-fluid level. A slight enhancement in the adjacent liver parenchyma was revealed. These findings were consistent with hydatid cyst superinfection.
There was also a mild dilatation of the intrahepatic bile duct adjacent to the lesion with an air bubble inside showing the presence of a cistobiliary communication.

Percutaneous abscess drainage, endoscopic retrograde cholangiopancreatography and posterior liver cystectomy were performed.
Hydatid cyst superinfection was confirmed and a Streptococcus salivarius was isolated.

Hydatid disease refers to human infection by the larval form of tapeworm, Echinococcus granulosus.
Hydatid disease involves the liver in approximately 75% of cases, the lung in 15% and other anatomic locations in 10%.
Radiological findings in hepatic hydatid disease depend on the stage of cyst growth and range from cystic lesions to a solid appearance [1-6]. In the early stages, Echinococcus cysts have the appearance of simple cysts. After daughter cysts develop, multiseptate wheel-like lesions are visualized. When the parasite dies, the septa disintegrate and wall calcification appears. The complete calcification may be assumed to indicate the death of the parasite but peripheral calcifications are common in both viable and nonviable cysts [1].

The WHO classification characterizes cysts by type and is based upon ultrasound appearance [7]:

- CE1: Unilocular anechoic cystic lesion with double line sign (active).

- CE2: Multiseptated, "rosette-like" "honeycomb" cyst (active).

- CE3a: Cyst with detached membranes (water-lily-sign), (transitional).

- CE3b: Cyst with daughter cysts in solid matrix (transitional).

- CE4: Cyst with heterogenous hypoechoic/hyperechoic contents; no daughter cysts (inactive).

- CE5: Solid plus calcified wall (inactive).

CT has a high sensitivity and specificity for hepatic hydatid disease. Intravenous administration of contrast material is not necessary unless complications are suspected, especially infection and communication with the biliary tree. CT usually shows a rounded, well-defined, hypoattenuating lesion with a distinguishable wall [6].

Rupture and superinfection are common complications of hepatic hydatid disease. Communication of hydatid disease with the biliary tree has been described in up to 90% of hepatic cysts. However, frank rupture into the biliary tree occurs in only 5-15% of cases [2, 3].
Cistobiliary communication may lead to obstructive jaundice, pancreatitis, cholangitis and sepsis with high mortality.
Dilatation of the biliary tree does not always indicate cyst rupture; it may result from direct compression of the biliary branches by the cyst or an associated common bile duct stone. Imaging plays an important role in the preoperative diagnosis of this condition which facilitates its management.
Infection occurs in <10% of cases and only after rupture of both the pericyst and endocyst. This allows the bacteria to pass easily into the cyst. CT is the modality of choice for demonstrating cyst infection that may manifest as poorly defined masses. Occasionally, patchy areas of contrast-enhanced liver parenchyma are seen in the vicinity of the lesion representing inflammatory changes. CT also most clearly depicts gas or air-fluid levels within the cyst [4, 5].