Excerpt from Hepatic Cysts

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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 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.

History of the Procedure

See Imaging Studies.

Problem

See Etiology and Clinical.

Frequency

The precise frequency of liver cysts is not known because most do not cause symptoms, but liver cysts have been estimated to occur in 5% of the population. No more than 10-15% of these patients have symptoms that bring the cyst to clinical attention. Hepatic cysts are usually found as an incidental finding on imaging or at the time of laparotomy. Most series in the literature are relatively small, reporting fewer than 50 patients each.

Etiology

Simple cysts

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 (see Media file 1) 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.

Polycystic liver disease

Adult polycystic liver disease (AD-PCLD) is congenital and is usually associated with autosomal dominant polycystic kidney disease (AD-PKD). Mutations in these patients have been identified in PKD1 and PKD2 genes. Occasionally, PCLD has been reported in the absence of polycystic kidney disease (PKD). In these patients, a third gene, protein kinase C substrate 80K-H (PRKCSH), has been identified. Despite these differences in genotype, patients with PCLD are similar phenotypically.

In patients with PKD, the kidney cysts usually precede the liver cysts. PKD often results in renal failure, whereas liver cysts only rarely are associated with hepatic fibrosis and liver failure.

Neoplastic cysts

Liver tumors with central necrosis visualized on imaging studies are often misdiagnosed as liver cysts. True intrahepatic neoplastic cysts are rare. The cause of cystadenomas and cystadenocarcinomas is unknown, but they may represent proliferation of abnormal embryonic analogs of the gallbladder or biliary epithelium. These cystic tumors are lined with biliary-type cuboidal or columnar cells and are surrounded by ovarianlike stroma. Cystadenoma is a premalignant lesion with neoplastic transformation to cystadenocarcinoma confirmed by tubulopapillary architecture and invasion of the basement membrane.

Hydatid cysts

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.

Hepatic abscesses

Hepatic abscesses can be amebic or bacterial in origin. Entamoeba histolytica is the causative agent in amebic abscesses. It is contracted by ingestion of food or water contaminated by the cyst stage of the parasite. Amebiasis generally only involves the intestine but can invade the mesenteric venules resulting in liver abscesses. Its only host is the human. Pyogenic abscesses can be a result of instrumentation but are most often caused by ascending cholangitis. Microorganisms isolated are most often bowel flora. Other routes of contamination include the portal vein and hepatic artery. Patients with intra-abdominal infections may present with liver abscesses with extension of bacteria through the portal venous system. Hematogenous spread via the hepatic artery in patients with septicemia is rare.

Pathophysiology

See Etiology.

Clinical

Simple cysts

Simple cysts generally cause no symptoms but may produce dull right upper quadrant pain if large in size. Patients with symptomatic simple liver cysts may also report abdominal bloating and early satiety. Occasionally, a cyst is large enough to produce a palpable abdominal mass. Jaundice caused by bile duct obstruction is rare, as is cyst rupture and acute torsion of a mobile cyst. Patients with cyst torsion may present with an acute abdomen. When simple cysts rupture, patients may develop secondary infection, leading to a presentation similar to a hepatic abscess with abdominal pain, fever, and leukocytosis.

Polycystic liver disease

PCLD rarely arises in childhood. These cysts are observed at the time of puberty and increase in adulthood. They occur as part of a congenital disorder associated with PKD. Women are more commonly affected, and an increase in cyst size and number is correlated with estrogen level. In PCLD, hepatomegaly may be prominent, and, occasionally, patients progress to hepatic fibrosis, portal hypertension, and liver failure. Complications, such as rupture, hemorrhage, and infection, are rare. However, patients do present with abdominal pain as the cysts enlarge.

Neoplastic cysts

Cystadenoma most often occurs in middle-aged women. However, cystadenocarcinoma equally affects both men and women. Most patients are asymptomatic or have vague abdominal complaints of bloating, nausea, and fullness. These patients, like all those with hepatic cysts, eventually present with abdominal pain. Rarely, they present with evidence of biliary obstruction.

Hydatid cysts

Patients with hydatid cysts, similar to patients with simple cysts, are most often asymptomatic, but pain may develop as the cyst grows. Larger lesions typically cause pain and are more likely to develop complications than simple cysts. At the time of presentation, patients generally have a palpable mass in the right upper quadrant. Cyst rupture is the most serious complication of hydatid cysts. Cysts may rupture into the biliary tree, through the diaphragm into the chest, or freely into the peritoneal cavity. Rupture into the biliary tree may result in jaundice or cholangitis. Free rupture into the peritoneal cavity may cause anaphylactic shock. As with simple cysts, patients with hydatid cysts may develop secondary infection and subsequent hepatic abscesses.

Hepatic abscesses

Patients with hepatic abscesses present with abdominal pain, fever, and leukocytosis. Clinical history is important because of associated illnesses. Those patients with amebiasis can have history of diarrhea and weight loss, although some may be asymptomatic. Pyogenic abscesses often present with cholangitis, abdominal infections, or sepsis. Rarely, abscesses will rupture, and patients present with peritonitis.

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