The patient was a known case of disseminated hydatid disease with multiple cysts in the liver, lungs, left shoulder region, as well as a paraspinal cyst. He underwent cardiac surgery with removal of the cyst under cardiopulmonary bypass. The surgeon aspirated some of the contents, injected cetrimide as a scolecidal agent and later excised the lesion. (see images 1 and 2). This is essentially a form of treatment based on the percutaneous approach termed PAIR (short for puncture, aspiration, injection of a scolecidal agent and re-aspiration). Local recurrence and secondary echinococcosis was found to be associated with spillage during removal of the cyst, incomplete removal of the endocyst and possibly the presence of unnoticed exophytic cyst development hence the need to inject material thet kills the scoleces before excising the cysts.
Imaging in this patient showed that the cyst was intrapericardial. There was no flow by color Doppler.
Discussion: Echinococcus granulosus, with its larval form, accounts for 95% of echinococcal infection. The life cycle of E. granulosus involves 2 hosts: definitive and intermediate. Dogs or other carnivores are definitive hosts, whereas sheep or other ruminants are intermediate hosts. Humans are secondarily infected by the ingestion of food or water that has been contaminated by dog feces containing the eggs of the parasite.
The freed embryo (oncosphere) enters a branch of the portal vein by passing through the duodenal mucosa after the outer capsule of the egg has been ingested. Most of these embryos become lodged in the hepatic capillaries, where they either die or grow into hydatid cysts. Some pass through the capillary sieve and become lodged in the lungs and other organs.
The wall of a hydatid cyst has 3 layers. The outer layer, or pericyst, consists of modified host cells, fibroblasts, giant cells, and eosinophils, which together form a rigid protective layer only a few millimeters thick. The pericyst represents the response of the host to the parasite. Middle layer is an acellular, laminated membrane that resembles the white of a hard-boiled egg and is easily ruptured. It has been reported that this membrane permits the passage of nutrients but is impervious to bacteria. On the other hand, the inner germinal layer is thin and translucent. Scolices (infectious embryonic tapeworms) develop from an outpouching of the germinal layer known as the brood capsule. Freed scolices, together with brood capsules, form hydatid sand, which settles in the dependent part of the cyst.
Although hydatid disease can involve almost every organ of the body, the basic US appearances are the same in most cases. Characteristic US findings are anechoic cystic lesions with usually well-defined margins, but they may vary according to the stage of evolution of the disease.
There are more than 15 classification schemes for liver hydatid cysts based on their US appearances; the initial classification by Gharbi et al and the World Health Organization (WHO)
classification are the most commonly preferred ones.
In Gharbi_s classification, hydatid cysts are classified into 5 types on the basis of their US appearances:
Type I, pure fluid collection
Type II, fluid collection with a split wall
Type III, fluid collection with septa
Type IV, hydatid cysts with heterogenous echo patterns
Type V, hydatid cysts with reflecting thick walls
WHO proposed an international consensus classification of US features of cystic echinococcosis (CE).
Type CE1 are unilocular, simple cysts withuniform anechoic content. A visible cyst wall and snow flake sign[ corresponding to hydatid sand are pathognomonic signs.
Type CE2 is a multivesicular, multiseptated cyst. Cyst septations produce wheel-like structures, and the daughter cysts indicated by rosette-like or honeycomb-like structures may partly or completely fill the mother cyst.
Type CE3, which has anechoic content with a floating membrane (waterlily sign) may also contain daughter cysts. Ultrasound features of type CE2 and CE3 are pathognomonic.
Type CE4 cyst with heterogeneous degenerative contents contain no daughter cysts, and a ball of wool sign that is indicative of degenerating membranes may be seen with this type.
Type CE5 cysts are characterized by a thick calcified wall.
Hydatid disease involving the heart is seen in 0.02% to 2% of cases, generally due to hematogenous spread or rupture of a lung hydatid cyst. It has rarely been reported in children. In cardiac hydatidosis, the most commonly affected chambers are the left ventricle (50%-60% of cases), interventricular septum (10%-20%), pericardium (10%-15%), right ventricle (5%-15%), and right or left atrium (5%-10%).
The hydatid cysts are unilocular (type I) or multivesicular (type II), although they may vary from types I to III.
Conclusion: Hydatid disease should be kept in mind when a cystic lesion is encountered anywhere in the body, particularly in patients from endemic regions.
We thank Dr. Mounir Obeid for providing us with the images of this interesting and rare case.
Gharbi HA, Hassine W, Brauner MW, et al. Ultrasound examination of the hydatid liver. Radiology. 1981;139:459-463.
WHO Informal Working Group. International classification of ultrasound images in cystic echinococcosis for application in clinical and field epidemiological settings. Acta Trop. 2003;85: 253-261.
Ahmet Tuncay Turgut, Okan Akhan Shweta Bhatt, Vikram S. Dogra, Sonographic Spectrum of Hydatid Disease. Ultrasound Quarterly & Volume 24, Number 1, March 2008