The liver

Pathological conditions

 

Benign tumours

The three most important benign tumours of the Liver are cavernous haemangioma, adenoma, and focal nodular hyperplasia. Cysts are frequently seen in the liver.
Haemangioma is the most frequently occurring liver tumour, both in adults and children, and is an important lesion to consider in the differential diagnosis of malignant tumours. On US a haemangioma is often seen as a hyper-echogenic localized lesion (Fig. 4). On unenhanced CT it is seen as a low-attenuation lesion but with intravenous contrast medium it exhibits a characteristic enhancement from periphery to centre within a few minutes (Fig. 5), a phenomenon that is particularly evident in large tumours. On MRI a haemangioma shows a high signal intensity on T2 weighted images with similar contrast dynamics to those seen on CT. Fine-needle biopsy of a haemangioma may yield only blood and this finding is not specific. The diagnosis is usually made on a combination of at least two imaging methods but angiography is rarely necessary.

Liver adenomas and focal hyperplasia (Fig. 6) (both of which are reported as being more frequent in females), may be isodense or hypodense on non-enhanced CT, but may show some transient enhancement with contrast medium.

	Figure 5. Contrast-enhanced CT of the liver. An initially low-density tumour is seen centrally in the liver (*) (upper left image). After contrast injection sequential scanning over three minutes shows contrast medium slowly filling in the tumour from the periphery to the centre. This fin ding is typical of a haemangioma.
	Figure 6. MRI of the liver. A high-signal les ion with a dark centre is seen anteriorly in the liver (arrows) on this sagittal, T1 weighted image. The finding is consistent with the diagnosis of nodular hyperplasia. The kidney is seen to the right, posteriorly.

Cysts of varying sizes are frequently seen in the liver and may be solitary or multiple. Multiple cysts in the liver, pancreas and kidneys are a feature of some specific disorders (e.g. autosomal dominant polycystic disease, von Hippel-Lindau disease). On US a cyst has characteristic features, with well-defined sharp borders, echo-free contents and peripheral echo enhancement. On CT the lesions are well defined, with contents approximating to the dens it y of water and exhibiting no contrast enhancement of either their contents or walls (Fig. 7). Cyst walls may rarely be

Figure 7. CT of the liver. A rounded structure is seen which has well demarcated walls and whose contents are of water density (*). No contrast enhancement is noted. These features are typical of a liver cyst. calcified. Hydatid cysts of the liver are common in endemic areas; they may show a characteristic appearance, especially on CT, with septa and walls that are frequently calcified (see Chapter 27).

 

Malignant tumours

Hepatomas or hepatocellular carcinomas are the commonest primary tumours of the liver. They occur with varying frequency in different parts of the world and are commoner in males than females. Cirrhosis and hepatitis B are predisposing factors. They are usually well shown on US, with both hypo- and hyper-echogenic areas (Fig. 8). On non-enhanced CT the tumour may be isodense and identified solely by the fact that it is a space-occupying lesion, but on contrast-enhanced CT the tumour is characterized by an uneven pattern of contrast enhancement, usually with areas of diminished density in the (necrotic) centre. There is often evidence of portal or hepatic venous invasion. It is important for surgical planning to delineate the tumour borders and localize the lesion with respect to the surgical lobar liver anatomy. This also applies to grading of the tumour with reference to any extrahepatic spread. In this respect, MRI may offer some advantage over CT, because of its multiplanar features (Fig. 9). The tumour may require differentiation from a cholangiocarcinoma (Fig. 10).

	Figure 8. US of the liver. Subdiaphragmatically there is a large 6 cm tumour (between arrows) which is of slightly higher echogenicity than the surrounding liver parenchyma, and which is well demarcated from it. These features are consistent with the diagnosis of a hepatoma.
	Figure 9. MRI of the liver (fat suppression STIR sequence). Posteriorly, a lobulated tumour of high signal intensity is seen, with several smaller satellite tumours. These features are consistent with the diagnosis of hepatoma.
	Figure 10. Contrast-enhanced CT of the liver. Centrally in the liver there is a large tumour (arrows) with dark areas of central necrosis and mixed attenuation in its periphery. In the ventral part of the liver a separate small lesion is seen (arrowhead), suggestive of a metastasis. This tumour, however, proved to be a cholangiocarcinoma,
	Figure 11. US of the liver. A large tumour of mixed echogenicity (between arrows) is seen which is well demarcated from the liver parenchyma (L). The tumour proved to be a metastasis from a breast carcinoma.
a	Figure 12. CT of liver metastases. (a) Two large, expanding lesions (arrows) are seen within the liver. They show mixed attenuation and enhancement, with dark areas of necrosis. In addition, two smaller lesions are seen in the lateral segment of the left lobe (arrow-heads). These tumours were metastatic deposits from an angioneurosarcoma. (b) A 2 cm metastasis (arrows) is demonstrated as a lesion with decreased contrast enhancement in comparison with the surrounding liver parenchyma. In this case the contrast medium was injected directly in the superior mesenteric artery, which is said to be the most efficient way to demonstrate small foci in the liver on CT. Note that no contrast medium is seen in the aorta.
b

The therapeutic embolization of liver tumours by catheter or direct injection is a technique in widespread use. Its value has not yet been determined with certainty, however, not least because embolization methods are continually evolving - a factor that makes long-term controlled trials difficult to conduct.

Figure 13. MRI of liver metastases. On this T1-weighted image two metastatic lesions (arrows) are seen, showing varying signal intensities.

The most frequent malignant tumours in the liver are metastases from other primary carcinomas. On US metastatic deposits may be seen as lesions which may be hypo- or hyper-echogenic in comparison to the surrounding parenchyma, or may show mixed echogenicity (Fig. 11). Metastatic lesions are usually multiple. On CT metastases are often seen as hypodense lesions that remain as such after the injection of contrast medium (Fig. 12). Certain metastases (e.g. hypernephroma) are hypervascular and therefore show increased contrast enhancement. MRI seems to be the most sensitive method for detecting liver metastases and the accuracy of the method may be enhanced by the use of magnetic contrast agents (Fig. 13). CT-portography may also help in the diagnosis of metastases.

Other focal lesions

Abscesses usually result from systemic infections, but may also result from a focus of infection elsewhere in the body, or be amoebic in origin. The abscesses may be solitary or multiple and vary in size and shape. On US an abscess is well seen, but the findings are non-specific. On CT abscesses are hypodense, with contrast enhancement of their peripheral wall (Fig. 14). On MRI there may be increased signal intensity on T2weighted images (Fig. 15), with contrast features similar to those seen in CT. Fine-needle biopsy is usually necessary to establish the diagnosis. Percutaneous drainage has become an important alternative to surgery in the treatment of hepatic abscesses.

Trauma to the abdomen may result in rupture of the liver, with the formation of an intraparenchymal and/or subcapsular haematoma. In these

	Figure 14. CT of the liver. Two typical abscesses are demonstrated, one showing a thick abscess wall (large arrow), the other showing a well demarcated smooth wall (small arrow).
	Figure 15. MRI of the liver. On this T2weighted fat suppression STIRsequence image multiple foci of increased density are seen, the cause being fungal abscesses of the liver. Only the largest foci were seen on ultrasound or CT, and this study shows the sensitivity of MRI in detecting small focal hepatic lesions.
	Figure 16. CT of liver trauma. Contrast enhancement brings out the hepatic veins, and CT demonstrates decreased perfusion of the right lobe of the liver, demarcated by the middle hepatic vein (arrow). This finding indicates that the artery of the right hepatic lobe is severed. A traumatic rift is also seen in the left lobe in the region of the falciform ligament. .
	Figure 17. US of fatty liver. The echogenicity of the liver is coarse and clearly increased in comparison with normal liver (the so-called "brightliver "-pattern). L = liver; K = kidney

cases the other parenchymal organs have to be studied for traumatic lesions as well, On US a rupture of haematoma is seen as a hypo-echoic area. The imaging method of choice in traumatic cases is contrast-enhanced CT (Fig. 16), which makes it possible to differentiate between haematoma, other fluid collections (bile) and normal parenchyma. On MRI a haematoma is seen usually as a lesion with increased signal.

Since many focal liver lesions, with the exception of cysts, do not show diagnostically characteristic features on any imaging method, fine-needle biopsy verification is usually essential to establish the diagnosis. For some liver disorders a cutting-needle biopsy may be preferable and this can be obtained with embolization of the track, particularly if there is a likelihood of haemorrhage (see below).

Parenchymal disease

Fatty degeneration of the liver is fairly common, especially with certain diseases such as alcoholism, diabetes or chronic infections. On ultrasound this condition may give increased echogenicity of the liver parenchyma ("bright liver") (Fig. 17). CT allows direct dens it y measurements of the liver, and since fat shows low attenuation this permits quantitative evaluation of the disease (Fig. 18). The degree of fatty

Figure 18. CT of fatty liver. The attenuation of the liver is markedly reduced, and clearly less than that of the spleen, a feature evident even without contrast enhancement. Note that the hepatic veins are visible against the dark liver parenchyma even without contrast enhancement. The density of the liver parenchyma (ROI 1) was measured as -5, 7 HU, and that of the spleen (ROI 2) as 37,5 HU. Very low and even negative attenuation values may be seen on CT of a fatty liver.

infiltration may change rather rapidly, according to the stage of the underlying disease. An attenuation of less than 30 HU is a clear indication of fatty infiltration. The changes may only be segmental or focal. Other focal lesions such as tumours or metastases, are well seen in a fatty liver, since they have normal density. A fatty liver is usually larger than a normal liver.

Liver cirrhosis may vary in appearance and depending on its aetiology the liver may be either smaller or larger than normal. Dynamic CT may show pathological patterns of perfusion of the liver and spleen, which may also be seen on colour Doppler US.

Clinical information is also important in the evaluation of parenchymal liver disease.

 

David J. Allison and Carl-Gustaf Standertskjold-Nordenstam