Hepatic simple cyst is one of the most common benign liver lesions, incidentally detected in 2-7% of the adult population. It is a thin-walled cavity lined by biliary epithelium containing clear serous fluid. Asymptomatic and requires no treatment or follow-up. Diagnostic criteria are definitive: water density, absence of enhancement, imperceptible wall, and absence of internal structure. When all criteria are met, diagnosis is definitive and no further workup is needed. Prevalence increases with age and may be multiple.
Age Range
20-80
Peak Age
50
Gender
Female predominant
Prevalence
Very Common
Hepatic simple cysts originate from congenital malformation of aberrant bile ducts. Intrahepatic bile duct remnants that lost connection with the biliary system during embryonic period undergo cystic dilatation through progressive fluid secretion. The cyst wall is lined by a single layer of cuboidal or flat biliary epithelium — this epithelium actively secretes fluid and contributes to cyst growth. Contents are clear, acellular serous fluid — protein content is minimal. On imaging, it shows water density because the content is pure transudate with X-ray attenuation coefficient identical to water. The cyst wall is avascular — contrast cannot reach the cyst interior, hence NO enhancement. The imperceptible wall results from single-layer epithelium being below imaging resolution threshold.
Imperceptible thinness of the anechoic cyst wall on US and bright posterior acoustic enhancement band behind the cyst. The combination of these two findings is pathognomonic for simple cyst — when wall thickening or nodularity is seen, simple cyst diagnosis is excluded and complicated cyst or neoplasm is considered.
Anechoic (completely echo-free), round/oval, well-defined lesion. Posterior acoustic enhancement is prominent. Wall is imperceptible — too thin to be detected by imaging resolution. No internal echoes, septa, or solid component. When all these findings are met, simple cyst diagnosis is definitive.
Report Sentence
Anechoic cystic lesion with posterior acoustic enhancement and imperceptible wall in the liver, consistent with simple cyst.
Homogeneous water-density lesion between -10 and +20 HU on non-contrast CT. Round/oval, well-defined, imperceptible wall. No calcification, septation, or high density. May be multiple. Densities >20 HU suggest proteinaceous or hemorrhagic content and question simple cyst diagnosis.
Report Sentence
Homogeneous, well-defined cystic lesion at water density (... HU) in the liver, consistent with simple cyst.
No enhancement on contrast-enhanced CT — density difference <10 HU between pre and post-contrast. Lesion remains at water density in contrast phases. Cyst remains dark while surrounding hepatic parenchyma enhances and becomes conspicuous. >15-20 HU enhancement excludes simple cyst diagnosis.
Report Sentence
Cystic lesion showing no enhancement in contrast phases (pre-post density difference <10 HU), consistent with simple cyst.
Very high signal on T2-weighted images ('light bulb'-like) — pure fluid content. Homogeneous, well-defined. Among the brightest structures on T2 HASTE or TSE sequences (similar signal to CSF). Markedly hyperintense on MRCP.
Report Sentence
Homogeneous markedly hyperintense cystic lesion on T2-weighted images, consistent with simple cyst.
Low signal on T1-weighted images — pure fluid content. Homogeneous hypointensity. High-protein or hemorrhagic cysts may be hyperintense on T1 and fall outside simple cyst diagnosis. No enhancement post-contrast.
Report Sentence
Homogeneous hypointense cystic lesion on T1-weighted images, consistent with simple fluid content.
Simple cyst shows no diffusion restriction on DWI. May appear hyperintense on DWI due to T2 shine-through effect, but high ADC value (>2.5 × 10⁻³ mm²/s) on ADC map confirms absence of diffusion restriction. Abscess or cystic tumors show diffusion restriction — this is absent in simple cyst.
Report Sentence
Cystic lesion showing no diffusion restriction (high ADC value on ADC map), consistent with simple cyst.
Criteria
Single, isolated cyst. Most common type. No follow-up or treatment needed. Size may range from millimeters to 20 cm.
Distinct Features
Single cyst, isolated, most common, variable size, no follow-up needed
Criteria
Multiple simple cysts — each meeting the same diagnostic criteria. Must be differentiated from polycystic liver disease (PCLD) — in PCLD cyst count is very high (>20) and liver is deformed. In isolated multiple cysts, PCLD family history and kidney cysts are absent.
Distinct Features
Multiple cysts, each meeting simple cyst criteria, differentiation from PCLD important
Criteria
Size >10 cm. Rarely may be symptomatic (abdominal pain, distension, compression symptoms). Complications: hemorrhage (intracystic hemorrhage), infection, rupture (very rare). Percutaneous aspiration-sclerotherapy or surgical fenestration may be performed for symptomatic giant cysts.
Distinct Features
Size >10 cm, rarely symptomatic, low complication risk, treatment only in symptomatic cases
Distinguishing Feature
Hemangioma shows peripheral nodular enhancement and centripetal fill-in on contrast CT — simple cyst has NO enhancement. Hemangioma is hyperechoic on US, simple cyst is anechoic. Hemangioma is T2 hyperintense but slightly lower signal than simple cyst ('light bulb' vs 'dimmer light bulb'). Simple cyst wall is imperceptible, hemangioma border is well-defined.
Distinguishing Feature
Biliary hamartomas (von Meyenburg complexes) are multiple very small (<15 mm) cystic lesions — may resemble simple cysts but are smaller and more numerous. May show thin-walled thin rim enhancement. Simple cyst shows no enhancement. 'Starry sky' pattern on MRCP is distinguishing feature of biliary hamartoma.
Distinguishing Feature
Hydatid cyst shows septations, membrane detachment (floating membranes), daughter cysts — simple cyst has NO internal structure. Wall calcification, pericyst, and complex internal architecture are common in hydatid cyst. Simple cyst is homogeneous anechoic with imperceptible wall. Endemic area and eosinophilia support hydatid cyst.
Distinguishing Feature
Abscess shows rim enhancement, internal debris, air-fluid level, and perilesional edema. Simple cyst has no enhancement, no internal structure, no perilesional changes. Abscess shows diffusion restriction on DWI (low ADC), simple cyst does not (high ADC). Clinical: fever, leukocytosis in abscess; simple cyst is asymptomatic.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upHepatic simple cyst is benign and requires no treatment or follow-up. Cysts meeting all criteria can safely be dismissed and should be stated in the report as 'simple cyst, no clinical significance'. Symptomatic large cysts (>5-10 cm, pain, compression, obstruction) may undergo percutaneous aspiration-sclerotherapy or surgical fenestration. Any atypical feature (enhancement, septa, thick wall, solid component, internal debris) precludes simple cyst diagnosis and requires further evaluation. BIOPSY IS CONTRAINDICATED — material obtained from simple cyst is non-diagnostic.
Simple cysts are benign and require no treatment. Very large cysts (>10 cm) may become symptomatic and fenestration may be needed. No risk of malignant transformation. Follow-up is unnecessary.