The term hepatic cyst usually refers to solitary nonparasitic cysts of the liver, also known as simple cysts. However, several other cystic lesions must be distinguished from true simple cysts. Cystic lesions of the liver include simple cysts, multiple cysts arising in the setting of polycystic liver disease (PCLD), parasitic or hydatid (echinococcal) cysts, cystic tumors, and abscesses. These conditions can usually be distinguished on the basis of the patient’s symptoms, clinical history, and the radiographic appearance of the lesion. Ductal cysts, choledochal cysts, and Caroli disease are differentiated from hepatic cysts by involvement of the bile ducts and are not reviewed in this article.
In patients with simple liver cysts, the general agreement is that laparoscopic unroofing offers the best balance between efficacy and safety. How patients with PCLD should be treated remains less clear because the failure rates for laparoscopic unroofing and fenestration are high. Liver resection, though more effective, carries higher risks. The treatment of hydatid cysts continues to be controversial. As more experience is reported in the literature, indications for PAIR (puncture, aspiration, injection, reaspiration) versus surgery are delineated.
The cause of simple liver cysts is not known, but they are believed to be congenital in origin. The cysts are lined by biliary-type epithelium, and perhaps result from progressive dilatation of biliary microhamartomas. Because these cysts seldom contain bile, the current hypothesis is that the microhamartomas fail to develop normal connections with the biliary tree. Typically, the fluid within the cyst has an electrolyte composition that mimics plasma. Bile, amylase, and white blood cells are absent. The cyst fluid is continually secreted by the epithelial lining of the cyst. For this reason, needle aspiration of simple cysts is not curative and recurrence is the norm.
Most patients with simple cysts are asymptomatic and require no treatment. When the cysts become large and cause symptoms, such as pain, treatment is warranted. Surgical treatment of simple liver cysts involves “unroofing” the cyst by excising the portion of the wall that extends to the surface of the liver. Excision of this portion of the cyst wall at the liver surface produces a saucer-type appearance in the remaining cyst so that any fluid secreted from the remaining epithelium leaks into the peritoneal cavity where it can be absorbed. Historically, treatment of symptomatic hepatic cysts required laparotomy, but, today, cyst unroofing can be successfully performed laparoscopically.
Hydatid cysts are caused by infestation with the parasite Echinococcus granulosus. This parasite is found worldwide, but it is particularly common in areas of sheep and cattle farming.
The adult tapeworm lives in the digestive tract of carnivores, such as dogs or wolves. Eggs are released into the stool and are inadvertently ingested by the intermediate hosts, such as sheep, cattle, or humans. The egg larvae invade the bowel wall and mesenteric vessels of the intermediate host, allowing circulation to the liver. In the liver, the larvae grow and become encysted. The hydatid cyst develops an outer layer of inflammatory tissue and an inner germinal membrane that produces daughter cysts. When carnivores ingest the liver of the intermediate host, the scolices of the daughter cysts are released in the small intestines and grow into adult worms, thus completing the life cycle of the worm.
Medical therapy with antihydatid agents (albendazole and mebendazole) is relatively ineffective. These drugs are used as adjuvant treatment, but they do not replace surgical or percutaneous therapy. In surgically treated patients, the use of antihydatid agents is generally given perioperatively; continuation is limited to those who have spillage of cyst fluid at the time of operation or to those with cyst rupture. Antihydatid agents are used in conjunction with percutaneous treatment. Medical therapy should be started 4 days prior to percutaneous treatment and continued either for 1 month (albendazole) or for 3 months (mebendazole), according to the World Health Organization (WHO) recommendations.
PAIR (puncture, aspiration, injection, reaspiration) is a percutaneous treatment technique for hydatid disease. In this minimally invasive method, a needle is introduced into the cyst under ultrasonographic guidance. Cyst fluid is aspirated and analyzed. Hypertonic saline or ethanol is then injected and reaspirated. PAIRD (puncture, aspiration, injection, reaspiration, drainage) is similar to PAIR except that a catheter is left in place after completion of the procedure. PAIRD is most often used for large cysts.