Complicated hepatic hydatid disease.

Clinical History

A Spanish patient with no previous clinical history presented with abdominal pain and a right upper quadrant mass which had been evolving for 1 month. Blood tests were normal.

Imaging Findings

On the ultrasound examination a large lesion in the right hepatic lobe is seen (segment 4). It is well circumscribed and hypoechoic. It measures 21 cm in diameter and has multiple small cystic lesions within.

A CT with intravenous contrast is performed to better characterize this lesion. It serves to confirm the presence of the liver lesion, with multiple small vesicles and incomplete linear calcification of the lower portion. It presents an exophytic growth, invading the right abdominal wall and causing pain to the patient. No intrahepatic biliary dilatation is evident.

Other small lesions with the same characteristics as the previous one are seen in the pelvis, probably due to spontaneous rupture and spread.

The patient was operated and Pathology concluded hydatid cyst caused by E granulosus.

Discussion

Hydatid disease is a worldwide zoonosis caused by larval stage of the tapeworm Echinococcus. In southern Europe the most frequent species is E. granulosus.

Humans are intermediate hosts who become infected through contact with dogs [1, 2]. The liver is the organ most commonly involved.

In 2003, the World Health Organization made an ultrasound classification of hydatid cysts. This new classification aims to reflect the natural evolution of lesions.

The liver hydatid cysts (HC) can be classified in five different types [3]:
Type 1 (cystic echinococcosis 1, CE1). Anechogenic, water attenuation, unilocular lesion or with echogenic mobile content inside (hydatid sand) that moves with postural movements producing the "snowstorm" appearance. It is a fertile lesion.
Type 2 (CE2). It is a multivesicular, multiseptate lesion. It shows a characteristic honeycombing appearance. It is a fertile lesion. The findings described are pathognomonic.
Type 3 (CE3). Unilocular lesion with floating detached membrane (water lily sign). It reflects a transitional state. These are pathognomonic findings.
Type 4 (CE4). Heterogeneous solid lesion without daughter vesicles, regarding cyst degeneration, which can also adopt spiral morphology (spiral sign) due to the degeneration of the membranes. Inactive lesion.
Type 5 (CE5). Lesion with thick and partially calcified wall, which can adopt ring or crescent moon morphology. This image is very characteristic and is caused by the death of the parasite. Inactive lesion.

Most frequent complications are [4]:

- Mass Effect. Occurs when HC become large and compress contiguous structures.

- Secondary bacterial infection, also known as superinfection.

- Breakage of the HC. As a consequence, HC can communicate with biliary ducts or it can be contained by the liver.

In the worst case, it can break into the peritoneal cavity. This can lead to acute abdomen with chemical or bacterial peritonitis [5].

In our case there is a pelvic cyst that results from breakage of a hepatic one. It shows similar characteristics as the liver one but it seems more homogeneous and has no mural calcifications.

It can also experience a transdiaphragmatic or intrathoracic rupture that communicates with the lung. It is characterized by the presence of air within the HC.

CT findings of breakage are:
- Structural deformity of HC.
- Intraperitoneal fluid collections and increased density of mesenteric fat.
- Presence of daughter cysts within the peritoneal cavity.

The treatment is usuallysurgical excision. Sometimes the treatment is supplemented with imidazole derivatives, which are the only treatment in unresectable cases, like this one.

Differential Diagnosis List

Final Diagnosis

Complicated hepatic hydatid cyst

URL:	https://www.eurorad.org/case/14087
DOI:	10.1594/EURORAD/CASE.14087
ISSN:	1563-4086