Benign intrahepatic lesions

14.1.4.1.1. Cysta

Typical appearence includes a well defined, anechogenic fluid-containing lesion with sharp margin. Usually thin septa can be included and wall calcification can be observed as well.

Their size varies between 3 mm and 10-12 cm.

The simple cyst (Figure 16) indicates a difference from the multicystic liver only in the number of the cysts. Conversely, the polycystic liver (Figure 17) is an autosomal dominant inheritant disorder, in which the cystic conversion can be present in up to 70-80% of the liver parenchyma due to the large number of the cysts. It often accompanies with polycystic

kidneys, whilst the entire polycystic syndrome – if also polycystic affection of the pancreas is also associated – occurs very rarely.

Figure 16: Simple liver cyst, US

183 Figure 17: Polycystic liver, contrast enhanced CT

Differentialdiagnostic difficulty is only given if the liver cysts show atypical appearence (its content becomes more hyperechogenic in US or more hyperdense in CT). In this situation, the differentiation from cystic tumor, metastasis or probably abscess is possible only if taking into account the clinical data and performing US or CT-guided punction.

MRI image shows a smooth contour characteristic to the cysts, which has low signal intensity on T1 and very high signal intensity on T2-weighted images. In case of a complicated cyst (fibrosis, condensation, hemorrhagia) various MRI signal intensities can be observed according to the complications.

Special determination is needed if the clinical features indicate the presence of Echinococcus cyst. In this case, serologic examinations have also an elemental importance. These disorders were discussed already in the parasitic liver diseases paragraph.

14.1.4.1.2. Hemangioma

Typical apprearence includes a well defined, hyperechoic solide lesion measuring usually less than 2 cm in diameter (Figure 18).

Figure 18: Typical US image of a hemangioma in the sixth segment of the liver In case of an atypical hemangioma (inhomogeous, mixed echostructure or hypoechoic appearence) additional imaging methods (multiphase MDCT, MRI) can be necessary, in addition in certain cases US guided biopsy can not be avoided in order to achieve the final diagnosis.

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MRI is only needed in case of "atypical" hemangiomas, since ultrasound is the best imaging method for diagnosing the hemangioma. If the ultrasound finding is uncertain, dynamic CT (Figure 19, 20), afterwards nuclear imaging and biopsy are the appropriate choices.

Figure 19: Hemangioma in the liver, native CT

Figure 20: Hemangioma in the liver, contrast enhanced CT

Paraarterial or subcapsular localisation, central thrombosis or fibrosis may interfere with the safety of diagnostic evaluation. In this case, MRI can be performed which is very sensitive to hemangiomas (size under 0,5 cm is also indicated – figure 21).

Figure 21: Hemangioma in the liver, T2 weighted MRI

185 Hemangiomas appear as a bit lower signal intense lesions compared to the liver parenchyma on the T1-weighted images.

A very high signal intensity can be observed on T2-weighted images. T2 relaxation time fluctuation (the strength of signal intensity by T2) is affected mainly by the extent of thrombosis/fibrosis.

Dynamic contrast MR study can be also performed, which demonstrates the slowed flow dynamics of the hemangioma (similarly to CT): haemangiomas fill up from outside inward as an iris or wheelspoke form in case of typical appearence.

14.1.4.1.3. Focal Nodular Hyperplasia (FNH)

Significant female dominance can be experienced considering its prevalence (80:20%). FNH frequently occurs in young women who have been taking anticoncipients for a long time.

No typical US appearence can be mentioned, because it can be hyperechoic, hypoechoic and even isoechogenic compared to the intact liver tissue. If it is a bit hyperechoic than the adjacent intact liver parenchyma, it can be reliably detected by US and (not in each case) a hypoechoic central area (central scar) can be also observed. In a typical case, spoke wheel pattern can be shown in the tumor by color Doppler. These tumors are typically arterially hypervascularised and a dominant artery running towards the center of the lesion can be also observed. FNH cannot be differenciated often by US from the adjacent liver parenchyma;

only the space occupying effect can be detected (moderate displacement, compression of veins, bile ducts). In these cases, a properly performed multiphase MDCT or MRI can have a diagnostic value (Figure 22). MRI shows on T1-weighted images that the signal intensity is isointense with the liver tissue, and only the vascular distorsion is the only sign which can draw attention to the present lesion.

Figure 22: FNH, contrast enhanced T1 weighted MRI, with intravenous gadolinium On the T2-weighted sequence, the signal intensity may be slightly increased compared to the normal liver parenchyma. Because of the fibrotic attribute of the "central scar", low signal intensity can be observed on both weighting, but if colliquation necrosis is present inside (some attribute this to the dilated biliary ducts), high T2 signal intensity can be observed.

14.1.4.1.4. Adenoma

Also by these benign liver tumors, a female dominance can be observed concerning its prevalence, but not in as rate as by FNH (60:40 %).

Its on-time detection is very important, because they can bleed during their increase resulting serious consequences (parenchymal or intrabdominal bleeding).

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No special morphology can be observed by US, however, a hypoechoic, avascular area with irregular contour inside the lesion can draw the attention to the bleeding.

In early arterial phase these lesions show an increased contrast enhancement as well, due to their hypervascularised feature from the direction of the hepatic artery, but there is no special sign (eg., central scar) as by FNH.

MRI shows usually a bit low signal intensity on the T1-weighted images. Pseudocapsule, if present, is hypointense on T1. Adenomas have high signal intensity on T2-weighted images.

The signal intensity is inhomogeneous because of the contained fat tissue and necrosis. The hemorrhages inside the adenoma provide a very „colorful‖ image and their signal intensities depend on the age of the hemorrhages on T1 and T2-weighted series.

The following features distinguish the adenoma from FNH: inhomogeneity, fat content, hemorrhages and, if present, pseudocapsule. The same features – except the fat content! - are not suitable to distinguish the adenoma from the hepatocellular carcinoma since the

hepatocellular carcinoma can also bleed and pseudocapsule can be also sorround it.

14.1.4.1.5. Other benign liver tumors

Lipoma, pseudotumor, intrahepatic splenosis, and other benign liver tumor can be also observed intrahepaticaly, obviously less frequently compared to the previously mentioned lesions. Diagnostic difficulties may be resulted in these cases, and imaging method guided biopsy can be sometimes necessary in order to draw the conclusions considering the next therapeutic decisions.

The most frequent