Cystic Liver Lesions
Cystic liver lesions are a heterogeneous group of changes that are often discovered incidentally. With the increased imaging for other reasons, the number of incidentally discovered liver cysts is rising. Earlier reports from laparotomies described a frequency of 0.2–1 %, while more recent ultrasound and CT studies indicate rates of 2.5–18 % [4-7].
Most cysts are harmless, nevertheless it is crucial to distinguish cysts with malignant or infectious potential, such as biliary cystadenomas/-carcinomas, choledochal cysts or echinococcal cysts. Certain risk constellations in ultrasound (septa, extensions/fenestrations, calcifications, wall thickening or nodules, irregular internal pattern, daughter cysts) require further clarification [8]. In addition, large or multiple cysts can cause complaints and must then be treated.
Simple Liver Cysts
Simple liver cysts are defined as thin-walled structures lined with cuboidal bile duct epithelium and filled with fluid (4). They arise from a malformation of the bile ducts but are not connected to the biliary system [9-10]. They can occur singly or multiply and are sometimes found together with other space-occupying lesions.
They are usually asymptomatic and discovered incidentally. They occur more frequently in women, increase with age [10], but have no connection to the pill or pregnancy. Only very large cysts usually cause complaints.
There is no indication for treatment or follow-up of simple liver cysts – regardless of their size – as long as no symptoms occur or no characteristic risk features are present.
Symptoms arise only with growth, rupture or pressure on neighboring organs → abdominal pain, feeling of fullness, shortness of breath, leg swelling due to vena cava compression.
Specific risk features in ultrasound (e.g., septa, fenestrations, calcifications, wall thickening or nodules, inhomogeneous internal structure or presence of daughter cysts) require further diagnostics using CT or MRI.
Diagnostics
Contrast-enhanced ultrasound represents the gold standard in the diagnosis of benign liver changes.
Computed tomography and MRI with specific contrast medium can further increase the sensitivity and specificity in the diagnosis of liver changes in combination with the ultrasound examination.
With a sensitivity of >95% and a specificity of >80%, contrast-enhanced ultrasound (“contrast-enhanced ultrasound”, CEUS) is a very good tool for the detection and discrimination of liver lesions. Critical in the application of CEUS are mainly 3 things. The contrast-enhanced ultrasound examination is much more examiner-dependent than the classic cross-sectional imaging methods.
In contrast to ultrasound examination and computed tomography, magnetic resonance imaging in principle also allows a statement on liver changes without contrast medium. Nevertheless, the use of liver-specific contrast media (which are primarily excreted biliary) is of high diagnostic relevance and offers essential additional information [3].
As with contrast-enhanced ultrasound, the contrast behavior over time serves for the imaging differentiation of liver lesions. Therefore, the use of a suitable contrast medium is also essential for this question in CT diagnostics. In at least 3, but better 4 contrast phases (native, arterial, portal venous, venous), most liver lesions can be assigned with very high sensitivity and specificity [3].
Simple hepatic cysts can already be diagnosed by a conventional ultrasound examination with a sensitivity and specificity of 90% [11].
Simple liver cysts are usually uniformly anechoic in the ultrasound image (i.e., completely black, without internal echoes), show good sound transmission (sound enhancement behind the cyst) and have smooth, sharply defined margins.
In CT, simple cysts show no internal structure, are hypodense with a fluid density below 20 Hounsfield units and exhibit no contrast uptake.
In MRI, simple cysts appear hypointense on T1-weighted images and hyperintense on T2-weighted images, also without contrast enhancement.
Tumor markers such as CA 19-9 can be elevated in up to 50 % of these patients due to secretion from the biliary cyst epithelium into cyst fluid or blood. A finding that is not necessarily associated with a malignant disease [11]. CA 19-9 is not suitable for distinguishing between simple cysts/PLD (polycystic liver disease) and mucinous cystic neoplasms [17,18].
Differential Diagnoses
Liver cysts with specific risk features in ultrasound (e.g., septa, fenestrations, calcifications, wall thickening or nodules, inhomogeneous internal structure or presence of daughter cysts) require further diagnostics using CT or MRI.
To be distinguished from the “uncomplicated” parenchymal cysts are other cystic formations:
- Caroli syndrome (congenital segmental cystic dilatation of the intrahepatic bile ducts)
- biliary hamartomas (von Meyenburg complexes)
- congenital polycystic liver disease (PCLD)
- Posttraumatic or hemorrhagic cyst (internal echoes, layering phenomena)
- Infectious cystic lesions
- Liver abscess (internal echoes, irregular wall)
- Echinococcus cysts (daughter cysts, wall calcifications)
- cystically appearing malignant tumors such as e.g.
- Metastases of an ovarian carcinoma
- Cystadenocarcinoma of the liver (septa, nodules, contrast uptake) [2]
Therapy
The treatment of symptomatic liver cysts aims to alleviate the symptoms and improve the quality of life by reducing the cyst volume.
Two procedures are available for therapy:
- Percutaneous aspiration with sclerotherapy (obliteration)
- Laparoscopic liver cyst deroofing
In aspiration with sclerotherapy, the fluid is aspirated from the liver cyst, and then the inner cyst wall is exposed to a sclerosing (obliterating) agent for a limited time.
Note: Aspiration alone is not sufficient, as recurrence almost always occurs.
Sclerotherapy initially often leads to a temporary reaccumulation of fluid, but subsequently causes a continuous reduction in cyst volume in most patients.
In laparoscopic cyst deroofing, the liver is exposed in the course of a minimally invasive operation. The cyst is punctured and emptied, then the cyst wall located outside the liver is resected (removed).
There are no reliable randomized controlled trials (RCTs) and no long-term data comparing these procedures to determine the best form of treatment. Although both methods are effective, surgical treatment has the lowest recurrence rate and also allows histological examination of the cyst [8,13-15].
The therapy decision should therefore aim to choose the least invasive procedure that at the same time achieves the best possible treatment outcome.
Follow-up checks are not necessary as long as no complaints occur.
Polycystic Liver Disease (PLD)
The rarely occurring congenital polycystic liver disease is often associated with polycystic disease of the kidneys and other organs. It leads in adulthood to progressive nodular hepatomegaly (which is sometimes massively developed). Nevertheless, liver function is extremely well preserved and portal hypertension develops only rarely.
Selected patients with massive hepatomegaly due to polycystic liver disease (PLD) can benefit from a surgical intervention.
Liver resection can be performed with acceptable morbidity and mortality and usually leads to rapid and sustained improvement in symptoms while preserving liver function.
Cyst fenestration and liver transplantation are also effective in selected patients, but not generally applicable to the same extent [19-21].