Simple cysts contain a clear, bile-like fluid. Because bile duct epithelium covers the simple cyst inner lining, it is hypothesized that simple cysts arise during embryogenesis when intrahepatic ductules fail to connect with extrahepatic ducts [7–10]: these aberrant ductules eventually dilate to form simple cysts.

Less than 4 % of simple cysts are almost always asymptomatic, but larger cysts greater than 5 cm especially when they reach a size over 10–12 cm and, particularly, are located in the left or anterior segments may cause compression of the stomach (Figs. 8.1 and 8.2) or modification of the abdominal profile with evident symptomatic manifestations [11, 12].

A not so rare complication is intracystic bleeding, generally due to an overwhelming size (over 15–20 cm). A surgical treatment is evidently indicated in this case.

Almost all patients have liver function tests within the normal range.

Ultrasound (US) is the best imaging modality to study simple cysts , which appear as a circular or oval, anechoic lesion with smooth borders and acoustic posterior enhancement and, in most cases, without internal septations [13] (Fig. 8.5). Also, ultrasound is strongly advised to monitor the evolution of these cysts: generally one time a year. Cysts that are found less than 3 cm at first diagnosis generally do not grow even in young patients. But we have been able to ascertain occasionally unexpected growth in size of small cysts. And therefore instrumental follow-up is generally advisable.

Further imaging studies, including computed tomography (CT scan) (Fig. 8.8) or magnetic resonance imaging (MRI) (Fig. 8.9), are not routinely required and show a nonseptated, round, and water-dense lesion. But in case of a surgical program due to a symptomatic disease, MRI is recommended to exclude communication with the biliary tree [14].

Symptomatic patients require therapy, either sclerotherapy or surgical fenestration .

Both forms have an autosomal dominant transmission and similar clinical presentation. PCLD associated with ADPKD is linked with mutations in the PKD1 (short arm of chromosome 16, encoding polycystin-1) or PKD2 gene (chromosome 4, encoding polycystin-2), whereas isolated PCLD is associated with heterozygous mutation in PRKC–SH or SEC63 genes [21–26].

How the gene mutations eventually lead to liver cyst formation has not been fully elucidated. Probably, a mutation in an individual intrahepatic bile duct epithelial cell results in a clonal expansion of the mutated cell, which loses communication with the intrahepatic bile ducts [27, 28].

There are some abnormalities in cholangiocyte proliferation and apoptosis and enhanced fluid secretion that are the key factors in the pathogenesis and in the progressive expansion of hepatic cysts in PCLD : cholangiocyte proliferation, fluid secretion, and cyst expansion.

Remodelling of the extracellular matrix surrounding the cysts by the activity of metalloproteases (highly elevated in liver cyst epithelia) is necessary for cyst expansion [29].

Hepatic cyst epithelium is sensitive to the proliferative effects of estrogens and IGF-1. Hereby, estrogens act not only directly but also by promoting the synthesis and release of growth factors from the cyst epithelium [30]. For this reason pregnancy, multiparity, and use of steroids further increase the risk for severe hepatic cystic disease.

The prevalence of isolated PCLD is estimated to be 1⁄100,000, while the prevalence of liver cysts in ADPKD is 58, 85, and 94 % in subgroups of age (respectively, 15–24, 25–34, and 35–46 year) [31].

Overall prevalence is the same in gender, but female population is associated with more severe liver disease.

Almost always, cysts are small and asymptomatic.

Moreover, in the majority of patients with ADPKD , PCLD is not normally the main cause of symptoms [28].

In a minority of patients (3 %), the expansion of liver cysts causes serious invalidating abdominal symptoms [32]. Data indicate that the annual growth of polycystic livers is about 0.9–3.2 % [32].

Symptoms normally begin in the third or fourth decade of life and are due to cyst growth. Presentation in childhood is therefore rare.

When present, symptoms are related mainly to the volume of the enlarged liver rather than to the volume of a specific cyst and include abdominal distension, dyspnea, epigastric pain, early satiety, vomiting, and shortness of breath [33].

Symptoms are exacerbated when there is compression of the portal vein, the inferior vena cava, or extrahepatic bile duct.

Some patients can suffer from malnutrition that is the main indication for liver transplantation.

Complications are infrequent and include bleeding, rupture, and infection of cysts [2].

The most severe complication is bacterial infection, especially in those who are under dialysis for ADPKD or in immunosuppressed patients after renal transplantation [2, 34]. The management consists of aspiration and drainage and antibiotic therapy. Cholestasis secondary to compression of adjacent biliary and portal hypertension secondary to portal or hepatic veins compression are rare.

Some patients may suffer from a rare complication as pruritus due to biliary obstruction even in the presence of normal laboratory tests [36].

Cerebrovascular pathology and cardiac-associated pathology (mitral valve prolapsed) occur respectively in 8 and 25 % of cases [37].

US shows multiple, fluid-filled, round or oval cysts with sharp margins being responsible for an extreme difficulty, by this tool, to identify vascular and biliary structures adjacent to the cysts. CT scan (Fig. 8.10) shows fluid attenuation with no contrast enhancement, while MRI demonstrates hyperintense on T2-weighted and hypointense on T1-weighted images [2] (Fig. 8.11). Both give a precise map of the liver and are mandatory to carry on a surgical approach.

A gastroscopy also may be useful to show a compression of the stomach or the duodenum causing early satiety, nausea, abdominal pain, and discomfort.

It is possible to stage the disease on CT scan findings according to Gigot’s classification [35] (Table 8.2) and Qian’s classification [34] (Table 8.3), while Schnelldorfer’s classification differentiates patients who could benefit from resection compared with transplantation [38] (Table 8.4).