Imaging the liver

The major advances which have taken place over recent years in surgical approaches to the liver and the enormous improvement in the safety of liver surgery are due to the careful individualised planning of surgery which is possible owing to the information obtained by preoperative imaging. The ideal choice of imaging modality is determined by the likely liver pathology and the locally available equipment and radiological expertise.

Ultrasound

This is the first-line test owing to its safety and availability. It is entirely operator dependent. It is useful for determining bile duct dilatation, the presence of gallstones (Fig. 52.4) and the presence of liver turnouts. Doppler ultrasound allows flow in the hepatic artery, portal vein and hepatic veins to be assessed. In some countries it is used as a screening test for the development of primary liver turnouts in a high-risk population. Ultrasound is useful in guiding the percutaneous biopsy of a liver lesion.

Computerised tomography (CT)

The current ‘gold standard’ for liver imaging is triple-phase spiral CT. This provides fine detail of liver lesions down to less than 1 cm in diameter and gives information on their nature (Fig. 52.5). Oral contrast enhancement allows visualisation of the stomach and duodenum in relation to the liver hilum. The early arterial phase of the intravenous contrast vascular enhancement is particularly useful for detecting small liver tumours owing to their preferential arterial blood supply. The venous phase maps the branches of the portal vein within the liver and the drainage via the hepatic veins. Inflammatory liver lesions often exhibit rim enhancement with intravenous contrast, whereas the common haemangioma characteristically shows late venous enhancement. The density of any liver lesion can be measured, which can be useful in establishing the presence of a cystic lesion. 

Magnetic resonance imaging (MRI)

MRI (Fig. 52.6) would appear to be as effective an imaging modality as CT in the majority of patients with liver disease. It does, however, offer several advantages. First, many patients are precluded from iodine-containing intravenous contrast agents because of a history of allergy. These patients should be offered MRI rather than contrast CT. Second, magnetic resonance cholangiopancreatography (MRCP) can produce excellent quality imaging of the biliary tract noninvasively. The image quality is currently below that available from endoscopic retrograde cholangiopancreaography (ERCP) or percutaneous transhepatic cholangio­graphy (PTC) but this is rapidly improving. Currently, it should be considered for diagnostic questions where ERCP has failed or is impossible due to previous surgery. Magnetic resonance angiography (MRA) similarly provides high-quality images of the hepatic artery and portal vein without the need for arterial cannulation. It is used as an alternative to selective hepatic angiography for diagnosis. It is particularly useful in patients with chronic liver disease and a coagulopathy in whom the patency of the portal vein and its branches is in question. 

Endoscopic retrograde

cholangiopancreatography

ERCP (Fig. 52.7) is required in patients with an obstructive pattern of liver function tests or in whom imaging has suggested an abnormality of the biliary tract. A preoperative check of coagulation is essential, along with prophylactic antibiotics and an explanation of the main complications which include pancreatitis, cholangitis and bleeding or perforation of the duodenum related to sphincterotomy. Endoluminal ultrasound of the biliary tract is possible using a ‘baby’ scope, and may provide additional information on the extent of hilar tumours. Therapeutic interventions are also possible at the time of ERCP and include stone retrieval, balloon dilatation of strictures, endoprosthesis insertion and brush cytology of turnouts to provide a tissue diagnosis.

Percutaneous transhepatic cholangiography

PTC is indicated where endoscopic cholangiography has failed or is impossible, as in patients with previous Polya gastrectomy. It is often required in patients with hilar bile duct tumours where endoscopic cholangiography fails to visualise the intrahepatic bile ducts (Fig. 52.7).

Angiography

Selective visceral angiography (Fig. 52.1) may be required both for diagnostic purposes and for therapeutic intervention. Prior to liver resection it may be used to visualise the anatomy of the hepatic artery to the right and left sides of the liver and to confirm patency of the portal vein. It can also provide additional information on the nature of a liver nodule, primary liver turnouts having a well-developed arterial blood supply. Therapeutic interventions include the occlusion of arteriovenous malformations, embolisation of bleeding sites in the liver and the treatment of liver tumours (chemoembolisation).

Nuclear medicine scanning

Radioisotope scanning can provide diagnostic information which cannot be obtained by other imaging modalities. Iodoida is a technetium-99m (99mTc)labelled radionuclide which is administered intravenously, removed from the circulation by the liver, processed by hepatocytes and excreted in the bile. Imaging under a gamma camera allows its uptake and excretion to be monitored in real time. These data are particularly useful where a bile leak or biliary obstruction is suspected and a noninvasive screening test is required. A sulphur colloid liver scan allows the liver’s Kupffer cell activity to be determined. This may be particularly useful to confirm the nature of a liver lesion, adenomas and haemangiomas having a lack of Kupffer cells and hence no uptake of sulphur colloid.

Laparoscopy and laparoscopic ultrasound

Laparoscopy is useful for the staging of hepatopancreatobiliary cancers. Lesions which have failed to be detected by conventional imaging are mainly peritoneal metastases and superficial liver tumours. Approximately 30 per cent of patients may have additional lesions detected by laparoscopy which have not been shown on good-quality planar imaging by CT or MRI. Laparoscopic ultrasound may increase this figure and provides additional information with liver tumours on their proximity to the major vessels and bile duct branches.

Fluorodeoxyglucose—position emission tomography

(FDG—PET)

This new imaging modality depends on the avid uptake of glucose by cancerous tissue in comparison to benign or inflammatory tissue. At present it is mainly used to determine the nature of a mass lesion demonstrated on another form of imaging. Deoxyglucose is labelled with the positron emitter fluorine-18 (15FDG) and this is administered to the patient prior to imaging by positron emission tomography (PET). A three-dimensional image of the whole body is obtained, highlighting areas of increased glucose metabolism (Fig. 52.8).