Liver cysts

Simple cysts and polycystic liver disease

A simple liver cyst (simple liver cyst) appears on ultrasound as a well-defined anechoic (devoid of internal echoes) lesion. It is characterized by the complete absence of a visible wall and the presence of posterior acoustic enhancement. In polycystic liver disease (polycystic liver disease), multiple lesions with similar characteristics are visualized.

On MRI, simple cysts exhibit a typical signal:

• Low (hypointense) signal on T1-weighted images (T1WI).
• High (hyperintense) signal on T2WI, the intensity of which significantly exceeds the signal from normal splenic tissue.

The main diagnostic challenge arises when complications occur, such as haemorrhage (haemorrhage) into the cavity. The presence of blood breakdown products can increase signal intensity on T1WI. In such cases, intravenous gadolinium-based contrast enhancement is mandatory for differential diagnosis from a neoplastic process. The main criterion of benignancy is the absence of contrast enhancement, which is most reliably confirmed on subtraction images.

Parasitic cysts: echinococcosis

Hydatid disease (hydatid disease) develops when parasite larvae migrate from the intestine to the liver, where they become encysted and provoke a local inflammatory response. The disease can remain asymptomatic for years, and serological testing is used to confirm the diagnosis prior to therapy or surgery. The risk of anaphylaxis during puncture exists, but successful cases of aspiration following medical preparation have now been described.

The imaging appearance ranges from features indistinguishable from a simple cyst to a complex mass. Features of a complex cyst include the presence of debris (hydatid "sand" composed of dead scoleces, prone to calcification), daughter cysts, membrane detachment, and wall calcification.

• Ultrasound: clearly visualizes debris, membrane detachment, and "cyst-within-a-cyst" daughter structures.
• CT: indispensable when massive wall calcification obscures the acoustic window on ultrasound. In the portal venous phase, peripheral calcifications and daughter elements are visible. In delayed phases, there is a complete absence of contrast enhancement of the wall and internal septa. This is a crucial criterion distinguishing a parasitic cyst from true neoplasms (e.g., biliary cystadenoma).
• MRI: details the internal structure but has low sensitivity to calcifications.

Liver abscesses

Pyogenic abscesses (abscess) most commonly result from portal pyaemia (portal pyaemia). The incidence of fungal and mycobacterial infections also increases in immunocompromised individuals. The pathogenesis involves a local inflammatory response, which over time is replaced by progressive central liquefaction (liquefaction) and the formation of an inflammatory "wall".

Diagnostics at various stages:

1. Early stages: prior to liquefaction, the lesion may mimic a solid tumor. On ultrasound, this is a spherical lesion with indistinct margins and low echogenicity.
2. Stage of liquefaction: ultrasound reveals a thickened, irregular wall and a necrotic center containing debris.
3. Contrast-enhanced CT: the abscess is visualized as a low-density area. Ring enhancement (rim enhancement) is typical, although this sign may disappear following the initiation of antibiotic therapy.
4. MRI: the lesion has low signal on T1-weighted images and high signal on T2-weighted images. These characteristics become more pronounced as the center liquefies.

Differentiating an abscess from necrotic metastases based solely on imaging findings is extremely difficult — aspiration or biopsy is often required.

Cystic metastases and solid mimics

Some malignant neoplasms (malignant cystic lesions) may have a predominantly cystic appearance. These include metastases from ovarian cancer, colorectal cancer, teratomas, and squamous cell tumors. Differentiating such metastases from abscesses without cytological and microbiological examination of a targeted aspirate is often impossible.

Among benign lesions requiring differential diagnosis, haemangioma (haemangioma) holds a special place. It is the most common benign liver tumor, consisting of vascular channels. Although it is solid, on MRI with a long echo time, haemangiomas yield a homogeneously high signal approaching that of fluid. Unlike malignant tumors (which become less conspicuous on such sequences), haemangiomas retain their lobulated contour and brightness. On dynamic contrast-enhanced MRI (Gd-DTPA), they demonstrate specific peripheral enhancement with progressive centripetal filling (fill-in).

Class and exam questions

What else to study on this topic

• Specific applications of Single-shot RARE sequences for the diagnosis of hemangiomas.
• Serological markers and laboratory confirmation protocols for echinococcosis.
• Criteria for the differential diagnosis of abscesses and necrotic metastases.
• Indications for diagnostic aspiration and ultrasound-guided technique.
• Rare benign solid tumors: adenoma and focal nodular hyperplasia.

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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