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If an abdominal ultrasound or CT scan found a cyst in your liver, it is most likely a simple liver cyst: a benign lesion, very common, and one that causes no problems in the vast majority of people. It is not a tumor, it does not turn into cancer, and it almost never needs treatment.
A cyst is simply a cavity filled with fluid. The simple liver cyst has a wall so thin it is barely visible, contains a clear water-like fluid, and does not connect with the bile ducts. It is usually an incidental finding, meaning it is discovered by chance on an imaging test ordered for another reason.
How common is it?
Very common. With the increasingly routine use of ultrasound and CT scans, simple liver cysts are detected in a sizeable share of the population, and that share rises with age. They are more common in women, especially the larger ones. Their size ranges from a few millimeters up to, in uncommon cases, lesions several centimeters across.
Does it cause symptoms?
Usually not. Most simple liver cysts are silent, and the person lives with them unaware. When a cyst is large (generally over 4 cm), nonspecific complaints may appear, such as pain or heaviness in the right side of the abdomen, early fullness when eating, or nausea.
It is wise to be cautious about attributing these symptoms to the cyst, because they often arise from other causes, such as irritable bowel syndrome, back pain, or gallstones. Complications, such as bleeding into the cyst, infection, torsion, or rupture, are rare and seen almost only in large cysts.
How is it evaluated?
In most cases, an abdominal ultrasound is enough for the diagnosis. The typical simple liver cyst appears as a rounded, anechoic lesion (black, because fluid does not reflect ultrasound), with no internal septa, imperceptible walls, and a characteristic bright reinforcement behind it. When the image has all these features and the cyst is small to moderate in size, no further tests are needed.
CT and MRI show a lesion with water density that does not take up contrast. They are reserved for doubtful cases: cysts with thick walls, septa, calcifications, or contents that do not look like pure fluid. In those cases, other lesions must be considered.
What can it be confused with?
The differential diagnosis of a simple liver cyst includes:
- Hydatid cyst: caused by the parasite Echinococcus granulosus (echinococcosis or hydatid disease). It is relevant in Chile, especially in rural and livestock-raising areas of the south and Patagonia, where the parasite cycles between dogs and sheep. Unlike the simple cyst, it usually has thick walls, calcifications, septa, or daughter cysts inside. When suspected, blood tests for antibodies (serology) are ordered, and it is not punctured without preparation, because leakage of fluid can trigger a severe allergic reaction and spread the parasite. The World Health Organization classifies these cysts by imaging to choose between observation, medication (albendazole), puncture, or surgery.
- Polycystic liver disease: when there are many cysts in the liver, polycystic liver disease should be considered, often associated with cysts in the kidneys (autosomal dominant polycystic kidney disease). It is a condition distinct from an isolated simple cyst.
- Abscess: a collection of pus, accompanied by fever, pain, and abnormal blood tests such as elevated C-reactive protein.
- Cystadenoma and cystadenocarcinoma: uncommon cystic tumors, one benign and one malignant. They have thick walls, septa, or nodules, and their treatment is surgical.
- Metastases or tumors with a fluid center: some tumors can have a necrotic area that mimics a cyst, but the rest of the image and the clinical context allow them to be distinguished.
Treatment
The vast majority of simple liver cysts need no treatment at all. If the cyst is small and has a typical appearance, there is no need even to repeat the ultrasound. For large cysts, follow-up imaging in a few years may be advised, and if it does not grow, monitoring is stopped.
Treatment is reserved for large cysts that cause clear and persistent symptoms. The preferred option is surgery, usually by laparoscopy, through fenestration (deroofing) of the cyst, which means opening and removing part of its wall so the fluid drains permanently into the abdominal cavity. Simple needle aspiration almost never solves the problem, because the cyst fills up again; to reduce that recurrence it is sometimes combined with injection of a sclerosing agent. These decisions are always made by your physician based on size, symptoms, and overall condition.
The bottom line is reassuring: in practice, a simple liver cyst is a finding without consequences, one that does not shorten life or force you to change your habits.
See also
References
- Pompili M, et al. Benign liver lesions 2022: Guideline for clinical practice - Part I - Cystic lesions (AISF, SIRM, SIC, SIUMB, AICEP, SITO, SIAPEC-IAP). Dig Liver Dis. 2022;54(11):1469-1478.
- Șirli R, et al. WFUMB Review Paper. Incidental Findings in Otherwise Healthy Subjects, How to Manage: Liver. Cancers (Basel). 2024;16(16):2908.
- Brunetti E, et al. Expert consensus for the diagnosis and treatment of cystic and alveolar echinococcosis in humans. Acta Trop. 2010;114(1):1-16.
- de Knegt RJ, et al. Management of benign liver tumors. Internist (Berl). 2020;61(2):140-146.
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