Overall Bottom Line

Cystic lesions of the liver represent a heterogeneous group of disorders, most of them with an indolent and benign course.
Cystic lesions of the liver are frequent and usually an incidental finding.
Widespread use of modern imaging has dramatically increased reports of the prevalence of simple cysts with rates as high as 18% on CT scan.
In some circumstances a surgical intervention is indicated by symptoms or to treat specific potential complications and morbidity related to the etiology of the cyst. Thus, efforts to characterize these lesions and arrive at a specific diagnosis should be made.

Section 1: Background

Definition of disease

Liver cysts are congenital or acquired fluid-filled spaces within the liver parenchyma that are lined by epithelium (true cysts) or that do not possess an epithelial lining (pseudocysts).

Primary hepatic and biliary cysts:
- Simple cysts.
- PCLD.
- Cystadenoma/cystadenocarcinoma.
- Bile duct cysts (Caroli disease).
Secondary hepatic and biliary cysts:
- Pyogenic liver abscess.
- Parasitic liver cysts (hydatid cysts, amebic liver abscess).
- Post-trauma.

Simple cysts: the female to male ratio is 4:1, and the prevalence is approximately 3%.
PCLD: the exact prevalence in the general population is unknown but it tends to be greater in women and increases with advancing age, severity of renal cystic disease and renal dysfunction.
Cystadenoma/cystadenocarcinoma: these are rare tumours (5% of the reported hepatic cystic lesions). Most occur in women older than 40 years of age.
Bile duct cysts (Caroli disease): more than 200 cases of Caroli disease have been reported in the literature. Caroli disease is a rare congenital disorder, defined by bile ductular ectasia without other hepatic abnormalities. Caroli syndrome is more frequent than the pure form of Caroli disease where there is associated hepatic fibrosis. The incidence of cholangiocarcinoma in Caroli disease is 10–20%.
Pyogenic liver abscess: the incidence is 25 per 100 000 pediatric admissions in the USA.
Parasitic liver cysts (amebic liver abscess): worldwide, approximately 40–50 million people are infected annually, with the majority of infections occurring in developing countries. The prevalence of infection is higher than 5–10% in endemic areas like South Africa and Bangladesh.
Parasitic liver cysts (hydatid cysts): the incidence of hydatid disease in the USA is very low, with approximately 200 cases presenting per year while in rural areas of developing countries it is largely endemic.
Post-trauma: rare.

Simple cysts: simple cysts are believed to be the result of excluded hyperplastic bile duct rests.
PCLD: AD-PCLD is an autosomal dominant disease that is associated with PKD. Affected individuals are found to have mutations of PKD1 (40–75%), and approximately 25% have mutations of the PKD2 gene.
Cystadenoma/cystadenocarcinoma: unknown.
Bile duct cysts (Caroli disease): development of these biliary cystic dilations is believed to result from the arrest of or a derangement in the normal embryologic remodeling of the large intrahepatic ducts.
Pyogenic liver abscess: hematogenous (portal, arterial), biliary or direct inoculation of bacterial infection from trauma.
Parasitic liver cysts (amebic liver abscess): Entamoeba histolytica
Parasitic liver cysts (hydatid cysts): Echinococcus granulosus (cystic echinococcosis) or E. multilocularis (alveolar echinococcosis), E. vogelii and E. oligarthros (extremely rare).
Post-trauma: trauma.

Not applicable for this topic.

Clinical: most of them are asymptomatic and found incidentally on imaging. Rarely, they may cause pain due to pressure, enlarging size, or bleeding into the cyst. Other causes for abdominal pain should be ruled out first before attributing the symptoms to simple cysts.
Laboratory: no changes on LFTs.
Histology: single layer of cuboidal or columnar epithelium (resembling biliary epithelium).
Imaging: found incidentally – see Figure 31.1.
On US a simple cyst is an anechoic unilocular lesion, with sharp, smooth borders and posterior acoustic enhancement.
On CT well-demarcated water attenuation lesion (water density –10 to +10 HU).
On MRI: simple cysts look hyperintense (bright) on T2-weighted images.

Clinical: abdominal pain, swelling, nausea, and anorexia.
Laboratory: no changes in LFTs unless the biliary tree is involved, then it can present with cholestasis (elevated direct bilirubin and AP).
Carbohydrate antigen 19-9 (CA 19-9) levels in the fluid may be increased. Pre-operative fluid sampling is not recommended because of the risk of disseminating malignancy in case of cystadenocarcinoma.
Histology: large multilocular mucin-filled cyst, with papillary projections resembling ovarian stroma. The lining epithelium is cuboidal or columnar. The cyst wall must be carefully assessed at surgical resection to rule out malignant transformation (cystadenocarcinoma).
Imaging:
- US: single, large, anechoic cysts. Some internal echoes showing septation secondary to papillary projections.
- CT: large cyst, with mural nodules, septations and calcifications.
- MRI: highly hyperintense on T2-weighted images. Can offer better resolution than CT to show septations and nodules (see Figure 31.2).

Clinical: abdominal pain, distention, postprandial fullness. Complications include: intracystic bleeding, extrinsic compression of the biliary tract and/or infection.
There is an association with cerebral artery aneurysm.
Laboratory: no changes unless the biliary tree is obstructed, then it can present with cholestasis (elevated direct bilirubin and AP).
Histology: single layer of cuboidal or columnar epithelium.
Imaging:
- US and CT: multiple fluid-filled round or oval cysts, with distinct margins in the liver and/or kidneys (see Figure 31.3).
- MRI: hyperintense on T2-weighted images and hypointense on T1-weighted images, except when they are complicated by hemorrhage.