Liver imaging in patients with history of suspected malignancy is important as the liver is a common site of metastatic spread, especially for tumours from the colon, lung, pancreas, and stomach, and in patients with chronic liver disease who are high risk of developing hepatocellular carcinoma (HCC). HCC is a common cancer that characteristically occurs in the setting of cirrhosis and chronic hepatitis virus infections. Hepatitis B and C report for approximately 80% of cases worldwide and currently HCC is the fifth most common malignancy in men and the eighth in women; its incidence is increasing radically in many parts of the world.
The purpose of this study is to highlight the suitability of a wide variety of imaging modalities available for the diagnosis of HCC, through an extensive literature search. The imaging techniques that are discussed include ultrasound (US), magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET) and finally angiography. In this study, comparisons are made between each imaging modality and various factors such as radiation dose, cost, availability, and the suitability of each modality in terms of medical screening are taken into account. In addition, the sensitivities and specificities of each imaging technique are considered. All these factors are used to assess each imaging technique for the detection of HCC. Chapter 1 Hepatocellular Carcinoma1.1 Introduction
Hepatocellular carcinoma (HCC) is one of the most common cancers; each year approximately 500 000 to 1 million individuals are diagnosed with HCC worldwide characteristically occurring in the settings of cirrhosis and chronic hepatitis virus infections. Hepatitis B and C account for more or less 80% of cases globally (Davis, et al 2008). Additional risk factors include hemochromatosis, ? 1-antitripsin deficiency, exposure to aflatoxins, (a mycotoxin produced by the fungus Aspergillus flavus, which is found in stored cereals and is a hepatic carcinogen when ingested), thorotrast administration, (which was used as a radiographic contrast agent and contains a high level of the radioactive isotope thorium, which emits ?-particles, leading to an intense radiation to the liver, which in turn may lead to hepatoma) oral contraceptives, and vinyl chloride exposure (Silverman, et al 2005). HCC is the fifth most common malignancy in men and eighth in women worldwide. Epidemiologically, HCC is most common in Asia and sub-Saharan Africa (Silverman, et al 2005).
According to the World Health Organisation, cancer is a leading cause of death worldwide, accounting for 13% of all deaths. Liver cancer accounts for 610,000 deaths and is the third leading cause of cancer – related death, exceeded only by cancer of the lung and stomach including liver cancers from metastases such as the gut (World Health Organisation 2008). Liver cancer is more common than cancer of the colon or breast. Liver cancer is a major health concern for both men and women and it is vital that early detection is made to reduce mortality rates. Early detection and staging of HCC are necessary for the more effective triage of patients and in planning management strategies (Digumarthy, et al 2005). There are many imaging modalities available for detection and characterisation of focal liver lesions (FLL). These include ultrasonography also known as ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) (Olivia, et al., 2004)
Until now, the most popular and leading method for detecting HCC has been US. Diagnostic accomplishment of US for HCC observation depends on many issues, but mostly the size and nature of the focal liver alteration, as well as the experience of the sonographer and the technical quality of the equipment. A study by Stefanuik, et al (2010) states that “as US examination is subjective and non-repetitive, all focal lesions suspected on US should be verified using CT, MRI and /or PET”. The use of these methods directs to a much more accurate diagnosis of HCC, with 89% of sensitivity and 99% of specificity (Stefanuik, et al., 2010).
This review covers current radiographic practice with respect to the imaging of HCC. These are reviewed, together with comparisons of imaging modalities in terms of accuracy, availability, management, and diagnosis, and an exploration of future HCC imaging issues. The research emphasises that US is not always the best imaging modality although new and improved methods have been applied for detecting HCC and that other imaging modalities can offer a more accurate diagnosis. With further research, HCC imaging techniques such as MRI, CT, and PET would become more widely available to improve the diagnosis of HCC.
1.2 Methodology
The aim of the study is to conduct research on Hepatocellular Carcinoma (HCC) imaging, assessing the suitability of imaging techniques available for the diagnosis of HCC. The method of choice for this research project was a wide range of literature search in all types of HCC imaging. The search included literature based on US, MRI, CT, PET and angiography imaging techniques. The review of the modalities chosen compares a number of different factors associated with medical imaging. It examines the imaging techniques with respect to the radiation dose received by the patient, including the risks connected with the imaging methods; the sensitivity and specificity of the modality; the cost and the availability of imaging equipment; and the suitability of each modality for HCC screening.
Ultrasound is the first and most widespread liver imaging method, therefore this study has explored the origins of this technique and any developments in this area. All the modalities have been discussed with reference to their diagnostic capabilities, as any liver imaging must be able to detect early signs of liver cancer. The literature search includes mainly peer-reviewed journal articles, and current reliable website information. Medical text books, NHS database, and journal searches have been carried out through the University of Cumbria library databases.
These searches and databases were efficient methods of finding relevant information regarding this subject. The key words applied in the search were ‘hepatocellular carcinoma’, which resulted in hundreds of articles. Further modification was undertaken by applying additional key words such as ‘management of HCC’, ‘imaging of HCC’, and ‘pathology of HCC’ shown in Table 1.
Table 1. Break down of Literature Review search of Different Imaging Modalities on Hepatocellular Carcinoma.
Search EnginesSearch TermsDates of inclusionNumber of hits Pub CentralImaging of HCC2003-2010350 Science DirectUltrasound imaging and HCC2001-2009100 Wiley ScienceHepatocellular Carcinoma2003-2010600 Pub MedFuture of HCC1997-200925It is important to note, with careful consideration of the literature obtained, is that all areas or research are subject to bias such as reviewer bias, inclusion bias, and publication bias. This should be taken in to account when any review is undertaken. Within this assignment, the author has tried to manage these elements by incorporating as many different views as possible, therefore attempting to counterbalance them (Swetnam, 2007). No ethical approval is required for this assignment.
The following chapter discusses the anatomy and physiology of the liver, which is essential in understanding the disease process and what imaging modality would be best suited for the diagnosis.
Chapter 2 Hepatocellular Carcinoma2.1 Anatomy and Physiology of the Liver
In order for the diagnosis of the HCC knowledge of the anatomy and physiology of the liver is essential. The liver is the heaviest gland of the body, weighing about 1.4 kg about 3lb in an average adult (Tortora & Derrickson, 2009, pg 945). The liver is situated inferior to the diaphragm and occupies most of the right hypochondriac and part of the epigastric regions of the abdominopelvic cavity (Tortora & Derrickson, 2009, pg 945). The anatomy of the liver can be seen in Figure 1.
Figure 1 Anatomy of Liver (Schiff, E.R 2007)
The liver is divided into eight independent functional units by divisions of the right, middle and left hepatic veins. The identification of these segments in each individual organ is the key to a reproducible meaningful description of where liver lesions are localised (Baert &Sartor, 2005).
Approximately 1500 ml of blood enters the liver each minute, making it one of the most vascular organs in the body. The blood supply to the liver constitutes 25% of the resting cardiac output via two main vessels; the hepatic artery and the portal vein. The hepatic artery, which is a branch of the celiac axis, supplies 25% of the total blood flow (Kumar & Clark, 2005). The portal vein drains most of the gastrointestinal tract and the spleen, delivering 75% of the blood flow to the liver. Both vessels enter through the liver via the hilum known as the porta hapatis, distributing blood to each of the eight segments which then passes into the sinusoids via the portal tracts. Blood leaves the sinusoids, entering branches of the hepatic vein which joins into three main branches before entering the inferior vena cava (Baert & Sartor, 2005). As the liver is the heaviest organ it also has many responsibilities ranging from; carbohydrate metabolism, lipid metabolism, protein metabolism, processing of drugs and hormones, excretion of bilirubin, storage and phagocytosis (Tortora & Derrickson 2009, pg 949).
2.2 Incidence of HCC
HCC is one of the most widespread internal malignancies. In a number of countries where there is a high incidence, HCC is the principal form of cancer; and on the whole, it rates as the fifth most common malignancy in males and the eighth in females (Silverman, 2005). However, in a recent study by Lau, (2008) it was found that the incident of HCC is raising in males (being the seventh most common) and females (ninth most common malignancy). In this particular study it was also found that at least one million new cases of HCC occur yearly, and death from the disease remains high regardless of treatments, with recent results it showed one-year, three-year, and five-year overall, and the survival rates were 66.1%, 39.7% and 32.5%, respectively; and for early stage patients it showed, 93.5%, 70.1% and 59.1% respectively. ( Lau, 2008)
Indeed, the incidence and mortality rates associated with the disease significantly overlap worldwide, as shown in Figure 2.
Figure 2: Incidence of HCC. (Lau,2008)
Vaccination against hepatitis B virus (HBV) has induced a decrease in HCC incidence in countries where the former is highly prevalent, whereas the contrary is true in areas where viral dissemination (mostly HCV) has occurred in the last decades. These data suggest that the geographic heterogeneity is related to differences in the exposure rate to risk factors and time of acquisition rather than to genetic predisposition. In this regard, studies in migrant populations have demonstrated that first generation immigrants carry with them the high incidence of HCC that is present in their native countries, but in subsequent generations, the incidence decreases (Schiffs, et al 2007).
The age at which HCC appears varies according to gender, geographic area, and risk factors associated with cancer development. In high risk countries with major HBV dissemination, the mean age at diagnosis is usually below 60 years, although it is not infrequent to observe HCC in childhood, thereby emphasizing the impact of viral exposures early in life. Contrarily, in intermediate – or low – incidence areas, most cases appear beyond 60 years of age. In all areas, males have a higher prevalence than females, the gender ratio usually ranging between 2:1 and 4:1, and in most areas the age of occurrence in females is higher than that of males (Schiff, et al 2007).
2.3 Aetiology of HCC
Vaccination against hepatitis B virus (HBV) has induced a decrease in HCC incidence in countries where this virus is highly prevalent, whereas the contrary is true in areas where viral dissemination (mostly HCV) has occurred in the last decades (Colli, et al 2006). These data suggest that the geographic heterogeneity is related to differences in the exposure rate to risk factors and time of acquisition, rather than to genetic predisposition. In this regard, studies in migrant populations have demonstrated that first generation immigrants carry with them the high incidence of HCC that is present in their native countries, but in the subsequent generations the incidence decreases (Schiffs et al 2007).
Ryder (2003) found in his study that HCC is a disease which will be seen as being common over the next few years in the UK, due to raising hepatitis C virus rates. When HCC is detected in patients the disease tends to metastasise to regional lymph nodes, lung and bones (Delbeke &Pinson 2003)
Table 2: Risk factors associated with HCC Adapted from Ahmed &Lobo (2008)
2.4 Pathology of HCC
The developmentof HCC from premalignant lesions is reported to occur in stages. The regenerative nodules evolve into dysplastic nodules divided into low and high grade. These may develop into early HCCs, and if left untreated can lead to advanced carcinomas (Silverman, 2005).
The gross pathology of HCC is a direct reflection of imaging findings
HCC most frequently occurs in the right lobe of the liver, either as single masses or as multiple small nodules. Occasionally, HCC may spread diffusely within the liver and may not be immediately obvious to the naked eye. The tumour tissue usually appears white, but necrosis, haemorrhage or bile staining may be present in the area. Invasion of veins is common and may lead to portal or hepatic venous obstruction. Arterial invasion is uncommon (Shearman,1997).
Macroscopically, small HCC around 2cm in diameter are divided into two types: a definite nodular type and an indefinite nodular type. The definite nodular type is seen as a clear nodule with a fibrous capsule or fibrous septa, whereas the indefinite nodular type shows only unclear nodular appearance with indistinct margins. Early HCCs have a unique blood supply, receiving blood from the portal vein in addition to the hepatic artery (Kojiro, 2005).
Microscopically, HCCs usually have a trabecular structure with thick cell plates and are relatively well differentiated so that their origins are identifiable. Many have a ductular or papillary pattern and pleomorphic, clear or anaplastic cells occur. Bile secretion by tumour cells into channels similar to canalculi can occur and is diagnostic when present.
Hepatocellular carcinomas are usually highly vascular and contain very little stroma. The vascular channels are lined by epithelial cells, few of which are true Kupffer cells. Venous invasion is common and occasionally widespread invasion of the surrounding sinusoids is seen. Careful examination sometimes can show that a HCC has a multifocal origin (Shearman, 1997).
In patients suffering from hepatocellular carcinoma, secondary spread is common (Nakashima, et al 1983). The most common sites of metastasis from HCC are the lungs (52%) and the lymphatic system (27%), usually occurring at the porta hapatis, celiac axis and around the pancreatic head.
Metastasis is seldom seen in the peritoneum, spleen, adrenal gland, bone, breast, brain, skin or muscles (Katyal, 2000). The carcinoma has a particular tendency to invade portal and hepatic veins, occurring in up to 62% of autopsy cases (Yu, 2004), and providing a channel for spread to the rest of the liver and (rarely) in a retrograde fashion into the superior mesenteric vein. The tumour being present in the portal vein is an important clue to the diagnosis of HCC, as fewer than 8% of portal vein tumours are due to other malignancies (Yu, 2004).Portal vein obstruction may not often lead to portal hypertension, while association of the hepatic veins may produce secondary Budd-Chiari syndrome and extension of the tumour into the right atrium is well-recognised (Kojiro, 1984).
2.4 Clinical Presentation and Symptoms of Hepatocellular Carcinoma
The development of HCC is usually silent in nature and it may go undiagnosed for as long as three years from the time of development. Common symptoms include abdominal pain, fatigue, and weight loss (Lai,2005). Abdominal pain occurs in 50% or more of the patients and is usually located in the epigastrium or right hypochondrium. It can be generalised and spread out through to the back or to the shoulders. Patients may present with jaundice, ascites, encephalopathy, or bleeding due to ruptured oesophageal varices. Acute hemoperitoneum due to ruptured HCC or bone metastases is the first sign in a minority of cases (Schiff, 2007).
According to Schiff, (2007) advanced HCC is associated with increased bilirubin, alkaline phosphatise, and ?-glutamyl transpeptidase levels. Hepatomegaly is often seen when a physical examination is carried out, giving hard and irregular palpable borders, although sometimes the liver may appear to be small and wasted. Paraneoplastic manifestations include hypocalcaemia, hypoglycaemia, feminisation, polycythemia, and watery stools. The right upper quadrant pain usually results from either hepatic capsular inflammation or complications related to the tumour, such as intratumoral hemorrhage or necrosis (Bhosale, 2006). Bhosale,(2006) found in his study that tumour invasion into the main portal vein can result in splenomegaly and ascites. He also found in his study that, when a large subcapsular tumour sustains blunt trauma or outgrows its blood supply, it may rupture into the peritoneal cavity causing a sudden severe onset of abdominal pain, pertonism, and hypotension.
Chapter 3 Hepatocellular Carcinoma3.1 Diagnostic Pathway
Diagnostic confirmation and careful staging of cirrhotic patients with HCC are key aspects for establishment of the patient’s prognosis and planning the right treatment. (Baert &Sartor, 2005). The diagnosis of HCC is based on a combination of clinical, laboratory, imaging and pathology examinations. However, with recent technological development in imaging, imaging studies play a crucial role in the diagnosis and staging of HCC. The most commonly used imaging techniques used for the diagnosis include US,CT, MRI, and angiography (Bruix &Sherman 2005)
A study carried out by Bialecki, (2005) recommends identification of early HCC which is potentially open to aggressive intervention and improved survival; this is the rationale behind screening for HCC. An effective screening program, however, requires certain criteria to be successful, which includes the following: a common disease with substantial mortality, an identifiable target group, acceptable tests with high sensitivity and specificity and available treatment (Bruix & Sherman 2005).
Histological diagnosis of HCC is usually by cytological examination of a suspected lesion usually achieved by fine needle aspiration biopsy (FNAB) and core biopsy, respectively, under US or CT guidance. Using both the FNAB and needle core biopsy simultaneously, rather than using one method gives a greater diagnostic accuracy respectively to any other diagnostic test (Bialecki, 2005).
Histopathological assessment was considered the principal method for the diagnosis of HCC and according to (Khan, 2009) it still remains so. It is compulsory to study non- tumoral liver issue to in order for the confirmation or to rule out the presence of liver cirrhosis as it could affect the treatment modality (Franca, 2004).
The European Association for the Study of the Liver (EASL) has devised an agreed statement to control the diagnostic approach in HCC patients, based on both the histological and radiological condition for recognising HCC in patients with cirrhosis. Recommendation were based on the size of the lesion (shown in Table 3); (Talwalkar, 2004).
Table 3 EASL agreed diagnostic criteria for HCC (Adapted from Bruix et al 2001 )
Recently, the American Association for the Study of Liver Disease (AASLD, 2005), issued a strategy which also projected a diagnostic approach for HCC (shown in Table 4 below). (Bruix, 2006).
Table 4. Diagnostic Criteria for HCC (Adapted from Bruix et al (2006)
A review that was conducted by Bruix &Sherman, (2005) suggested the following workup (shown in figure 3); it was devised by the panels of experts from the EASL to offer guidelines for the clinical management of suspected HCC lesions.
Figure 3: A suggested algorithm for nodule investigation found in Ultrasound during screening or surveillance. (Bruix & Sherman 2005).
HCC lesions greater than 2 cm, can be diagnosed non-invasively based upon radiographic criteria in patients with cirrhosis ( Talwalkar, 2004). However, detection of nodules with arterial hyper-vascularisation in any imaging modality; ultrasound, CT or MRI, or with a single imaging modality, with the association of an increased Alpha-fetoprotein level of 400ng/ml in cirrhotic liver, is highly considered as a diagnosis of HCC (Torzilli, 1999). EASL recommended the evaluation of hepatic nodules should be carried out with US, contrast-enhanced CT, or MRI with official angiography used in cases of diagnostic uncertainty (Haung, 1996).
Durand, (2001) concludes that nodules smaller than 1cm detected by ultrasound are established to be non-malignant in half of the cases, and a sensible protocol is to repeat ultrasound scanning every three months awaiting the growth of the lesion to achieve 1 cm or above in diameter. Nodules that are between 1-2cm in size are expected to be HCC and pathological evidence was recommended by using fine-needle aspiration or biopsy (or even both) for the diagnosis of these nodules. (Durand, 2001).
3.1 Staging of Hepatocellular Carcinoma
A number of staging systems have been developed to stratify patients into a suitable risk group where information on prognosis and the (right for) treatment can be obtained. Staging of HCC is important to clinical management and is assessed through either the tumour lymph node (TNM) system or the Okuda classification system. The primary lesion is defined by tumour size; number and the site of the lesions; invasion of local vascular structures; and extension into the biliary system (Table 5); (Marsh, 2000).
T1 lesions are those that are solitary tumours without vascular invasion. T2 lesions are solitary tumours with vascular invasion or multiple tumours, not larger than 5cm. T3 represents multiple tumours larger than 5 cm, invading the major portal or hepatic venous structures. T4 lesions are tumours that have directly invaded adjacent organs. The use of the binary, lymph node staging consists of -N0 without regional metastasis and N1with regional lymph node metastasis. Distant metastasis and M1 being the presence of distant metastasis (Silverman, 2005).
Table 5. TNM staging system devised by the American Joint Committee on Cancer (Marsh, J.W. 2000)
According to Golfieri et al (2007) the TNM system has been tailored constantly having no prognostic accuracy and agreeing to this is a study by Olivia & Saini
(2004), adding that the system is limited in use because it is based on pathological findings, and liver function is not considered. The use of the Okuda classification, however, has been described as potentially suitable for patients with advanced HCC (Bolondi, 2003)
Although the Child-Pugh classification, was originally used to assess and predict mortality during surgery, it is still used today to assess the prognosis of chronic liver disease (mainly cirrhosis), including liver transplantation (Sarna, 2008). This is described below in Table 6.
Child-Pugh Classification
Points123 Albumin>3530-35>30 Bilirubin<5050-75>75 Prothrombin Time>6040-60<40 AscitesNONEMILDTENSE EncephalopathyNONEI-IIIII-IVTable 6. Child-Pugh Classification of severity of liver disease according to the degree of ascites adapted from Ahmed & Lobo (2006)
The negative aspect of the Child-Pugh system is that it considers only liver function, thus is not accurate (Christensen, 2004).
Several scoring systems have been created in the last few years, trying to stratify patients according to expected survival. However, most classification methods do not take into account the effects of treatment for different disease stages; when comparing results amongst staging systems none has been adequately cross-validated (Bruix & Sherman 2005).
Recently a study compared on staging systems by Marrero et al (2005) and Grieco et al (2005) validated the Barcelona-Clinic –Liver Cancer (BCLC) staging system. Figure 4.
Fig. 4. Strategy for staging and treatment assignment in patients diagnosed with HCC according to the BCLC proposal.(Adapted from Bruix &Sherman 2005)
This BCLC staging system uses variables related to tumour stage, liver functional status, physical status, and cancer-related symptoms, and links the four stages as described in the above figure. In brief, it identifies individuals at stage ‘0’ with very early HCC who may benefit from resection, those at stage ‘A’ with early HCC are candidates that may benefit for radical therapies (resection, liver transplantation or percutaneous treatments). Patient ‘B’ with intermediate HCC may benefit from chemoembolisation. Patients at stage ‘C’ with advanced HCC may receive new agents in the setting of randomised controlled trials, and patients at stage ‘D’ with end stage and a very poor life expectancy should receive symptomatic treatment.
3.2 Tumour Markers
There are a number of tumour markers, and several are currently used in clinical practice as a method for the detection of HCC as shown in Table 7.A particular protein produced by cancer cells can be used as a tumour marker, although small amounts of materials are also created from non-cancer cells. Therefore, the sensitivity and specificity of these markers must be taken in to account (Khan, 2009). Conversely, recent studies have publicised that the creation of such tumour markers replicate the biological nature of malignant grade, leading to the calculation of tumour progression and poor prognosis (Masuzaki, et al.,2008). The most frequent serum marker used is the Alpha-fetoprotein (?FP), (Khan, 2009).
Table 7 showing serum markers for HCC (Khan, 2009)
Khan, (2009) describes in his study that ?FP is a normal serum protein, amalgamated by foetal liver cells and york sac cells. Patients with chronic liver disease, those associated with a high number of hepatocyte regeneration, can convey ?FP in the absence of cancer. It is seen that ?FP is elevated in hepatocarcinogenesis, embryonic carcinomas, and in gastric and lung cancer (Grizzi, 2007). Alpha-fetoprotein has been used as a tumour marker for many years. In the years before the invention of sensitive imaging techniques such as US, CT and MRI, ?FP was considered to be equally sensitive and specific for HCC but now it is known not to be the case (Davis, 2008)
Alpha-fetoprotein is not always elevated in patients with HCC. Some patients carrying cirrhosis and hepatic inflammation can have elevated ?FP without the presence of a tumour. Alpha-fetoprotein levels <20 ng/mL are considered to be normal (Khan, 2009). The test tends to give a value of 39-65% for the sensitivity and 76-94% for the specificity with a optimistic prognostic value of 9-50% for the existence of HCC in published studies (Daniele, 2004).
Conversely, a debate by Franca,(2004) states that a higher value about 400-500 ng/mL gives a better diagnostic value for HCC in patients with cirrhosis. However, such a cut -off value is difficult in complete diagnostic terms, since high levels of this value are not always seen in the presence of small tumours <5cm; only 30% of HCC patients have levels higher than 100 ng/mL. In contrast Omata,(2010) finds in his review, receiver operating curve anaylsis of ?FP used as a diagnostic tool suggest that a value of about 20ng/mL provides the most favourable balance between sensitivity and specificity. In a meta-analysis , ?FP with a cut-off value of 200ng/mL showed a better combined Positive likelihood ratio (LR+) than with the normal 20ng/mL, suggesting that the cut-off value for ?FP should be set to 200ng/mL, rather than the normal value of 20ng/mL for the diagnosis of HCC (Tateishi, 2008).
Limitations in the specificity and sensitivity of ?FP in observation of high risk populations have combined the use of US as an additional tool for the detection of HCC . The Senitivity of US is 78-90%, giving a specificity of 93%(Omata, 2010). In some countries such as Japan, associated measurement of des-c-carboxyprothrombin (DCP) and lens culinaris agglutinin-reactive fraction of ?FP (?FP-L3) supposedly increases the detectability of small HCC. The use of CT or MRI with contrast medium can attain a higher diagnostic accuracy than US, but their use is expensive (Oka, 2001).
Therefore, it is clearly accepted that ?FP is not an ideal tumour marker for early detection of small HCC. However, it is still used in the role of diagnosing HCC, since in cirrhotic patients with a mass in the liver; an ?FP having a greater value has a very high diagnostic value for HCC (Bruix &Sherman, 2005)
3.3 Liver Biopsy
Diagnosis of hepatic lesions with liver biopsy has been widely used for over a half century. When liver biopsy is performed it offers a safe and effective means to confirm suspicious lesions for HCC (Bialecki, et al., 2005). Samples can be obtained for cytology and histology purposes by percutaneous FNA and core biopsy, respectively either by US or CT guidance. Using both FNA and core biopsy techniques gives a greater diagnostic accuracy than when either is used alone (Wang, et al., 2007).
Liver biopsy is not need to be performed when the diagnosis is certain after clinical, laboratory, and radiographic imaging is applied. In a situation of cirrhosis, a solid and hypervascular lesion that expresses late washdown should be considered to be HCC ( Davis, et al.,2008). Without preoperative verification of HCC by liver biopsy many studies show the rate of false-positive diagnosis being considerable in patients with small tumours (Caturelli, et al., 2004).
According to Hayashi, et al., (2004), false-positive rates can be high as 33% after histological examination.
Significant advances in imaging techniques have submitted a sensitivity ranging from 89-96% in the diagnosis of liver cancer, thus reducing the need for liver biopsies ( Maturen, et al.,2006). The comparison of ultrasound-guided fine- needle biopsy, imaging methods can eliminate the risk of tumour seeding in the biopsy-needle track whilst being less limited by invasiveness ( Baert & Sartor, 2005). However, consensus by Solmi, et al.,(2004), suggests the risk of false-positive results from imaging technique should not be ignored. On the other hand, current literature suggests that the specificity of FNA or the diagnosis of HCC is almost 100%, although its sensitivity ranges from 83.3%-97.5% (Wang, et al.,2007).
Complications that are linked with liver biopsy are rare and can be avoided by using one stick approach, such as coaxial technique and liver biopsies should be avoided when platelet counts are <50 000 per mm3 (Bialecki, et al., 2005). The risk of seeding depends on many factors, including needle calibre, number of passes, tumour histology and lesion location (Solmi, et al., 2004). The possible spread of tumour from the biopsy needle track is of great worry and increases much of the argument surrounding the need for liver biopsy. Although many studies show rates as high as 5%, and many larger studies specify the risk being as close to 1% ( Bialecki, et al.,(2005). Taking in to account the possible risk of biopsy and its precision, a diagnostic biopsy should only be performed if the result has a clinical impact, or if there is a significant risk in the treatments planned, against the background of a possible false-positive diagnosis based exclusively on imaging techniques (Fung, et al.,2004).
Chapter 4 Hepatocellular Carcinoma4.1 Introduction to Imaging Modalities
Diagnostic confirmation and assessment of HCC are crucial for the accurate clinical management of patients. The analysis of HCC is based on imaging examinations in combination with clinical and laboratory findings. However, with recent technological development in imaging, imaging plays a crucial role in the diagnosis and staging of HCC. Regardless, the detection of smaller tumours continues to be difficult, especially in cirrhotic patients whose parenchymal architecture is abnormal. (Bialecki, 2005).
HCC is the most common primary malignant hepatic neoplasm taking place in patients with chronic hepatic parenchymal disease (Harisinghani, 2002). Patients with chronic liver disease such as hepatitis C are mostly at risk in developing HCC and tend to undertake periodic liver screening for focal liver detection. Screening with ?FP and US is a useful tool for the early diagnosis of HCC (Olivia, &Saini, 2004).
Discovery of focal masses within cirrhotic liver is a daunting challenge. However, difference of HCC from other solid lesions such as regenerating nodules, (RN) dysplastic nodules, (DN) and confluent hepatic fibrosis is as equally important and difficult task (Harisinghani, 2002). Baert & Sartor (2005) conclude that one of the key pathologic factors for the differential diagnosis that reflects in imaging appearance is the vascular supply to the lesion.
Focal lesions in patients with cirrhosis should be suspected of HCC. The abdominal imaging to detect HCC has improved over the last two decades, and the methods have generally replaced more invasive procedures such angiography, exploratory laparotomy, and percutaneous biopsy as the preferred tools to identify hepatic tumours. Regardless of this progress, however, ultrasound, CT and MRI remain unpredictably insensitive for detecting HCC particularly with tumours <2cm in diameter (Snowberger, 2007).
Furthermore, Taouli & Krinsky (2006) elaborate that much of the older radiologic literature overvalued the sensitivity of imaging methods since no connection with whole organ pathology was available. New hardware and software technology that was introduced to CT and MRI in the 2000’s showed enhancement in sensitivity in both modalities. MRI is the most sensitive method and identifies 80% of tumours, including 63% of tumours <2cm, whilst CT scanning identifies 70% and ultrasound about 60% (Snowberger, 2007).
To choose which imaging modality is best one must consider that the modality must be sensitive in detecting hypervascular lesions. It must be able to differentiate between arterioportal shunts and true lesions. It should be able to recognize the supporting imaging features of HCC such as pseudocapsule, internal septa, and mosaic appearance as shown in figure 5(a-c). (Thng, & Kuo, 2004).
Figure 5 (A-C) HCC in chronic hepatitis C patient (Thng, & Kuo, 2004)
Figure 5 a) Arterial phase helical CT shows a multinodular mosaic pattern with a central necrotic scar.(b) Delayed phase helical CT shows an enhancing pseudocapsule (as indicated by the white arrow).(c) The cut surface of the gross specimen shows a similar multinodular mosaic pattern. Note the presence of the pseudocapsule (as indicated by the black arrows).
There are many imaging modalities and diagnostic tools employed for the characterisation and detection of HCC; these are US, CT, MRI, PET and angiography. Conversely, plain film imaging is completely non-specific for the detection of HCC; although it may identify a calcified abdominal mass in a very extreme case (Olivia &Saini 2004). Since technological advances in these modalities and their association with contrast media continues to improve, no broad consensus currently exists to which modality should be used (Olivia &Saini 2004).
4.2 Ultrasonography
US is becoming the most popular method for the detection of HCC. Recent advances in digital technologies have resulted in remarkable development in the field of imaging modalities. US is one modality that has shown significant improvements within the past decade. For the diagnosis of liver tumours, US in the clinical setting have the advantages of real- time observation, a simple technique, and non-invasiveness (Nicolau, 2004). As ultrasound is widely available it is also less expensive than other imaging modalities and at a high frequency, it is a first step, reliable method for the diagnosis of liver tumours (Maruyama, & Ebara, 2006). Further, Maruyama & Ebara (2006) echo their own views that the use of Doppler method and micro bubble contrast agents provide details of haemodynamic, which are useful for the detection and the characterisation of liver tumours, and that US allows 3D visualisation of combined tissue structures and colour blood flow appearance. US guidance techniques allow the accurate percutaneous advancement of needle biopsy and treatment (Schiff , 2007).
The diagnostic success of US for HCC surveillance depends on many factors, particularly the size and character of the focal liver changes as well the experience of the sonographer in accordance with the technical quality of the US equipment (Colli, 2006). However, Bolondi (2006) states that one major drawback has been its limited impact in the detection and characterisation of focal liver lesions; many prove difficult to detect because their echogenicity is indistinguishable from the surrounding liver. However, in the B-mode (baseline) ultrasound, these isoechoic lesions and their haemodynamics have often proved to be non-specific, slightly adding improvements in the ability to detect distinct vascular structures.
A recent literature study concluded by Choi, & Lee, (2010) evaluated the accuracy of US for detecting HCC, and demonstrated that the sensitivity was 60% and the specificity was 97%. In a recent study by Hatanaka, (2008) demonstrated that contrast enhanced US has sensitivities, specificities, and positive predictive values of greater than 90% in the diagnosis of HCC.
4.3 HCC Screening with Ultrasound
Review of the literature offers the straight forward conclusion that the use of US as the imaging modality of choice for the HCC screening is widely accepted; this technique is a rapid and non-invasive evaluation of liver parenchyma. As previously mentioned, US is relatively inexpensive, does not expose the patient to ionising radiation and is readily available (Soye, 2007). However, according to Baert & Sartor (2005), a complete ultrasound assessment of the liver parenchyma may sometimes be impossible due to the patient’s size and body habitus or even the colonic interposition.
In accordance with the most recent literature, the combination of serum ?FP with US improves detection rates. The best possible diagnostic tests in a observation program should be measured from the view of cost efficacy, because it is clear that more regular tests can detect HCC nodules of smaller size. Many recent studies have adopted an interval of six months between periodic diagnostic tests, although there are no randomised studies that have determined the optimal interval (Omata, et al 2010). In cirrhotic patients the suspicion of early HCC should be raised when a new small focal liver lesion (FLL) is detected during follow up US as more than 50% of the FLL found in liver cirrhosis are HCCs (Nicolau, et al 2004).
According to Bolondi et al (2007) there is not enough data to actually compare the sensitivity of conventional US with screening programmes. However, it should be outlined that a recent study carried out by Omata, et al (2010) concurs that most ?FP studies have a cut-off value of 20 ng/mL with sensitivity ranging from 49 to 71 % and a specificity from 49 -86% in HCCs smaller than 5cm. The limitations in the sensitivity and specificity of ?FP in surveillance -of elevated risk populations have led to the use of US as a further method for the detection of HCC.
An Omata, et al (2010) study found that in some countries, such as Japan, associated measurement of des-?-carboxyprothrombin (DCP) and Lens culinaris agglutinin-reactive portion of ?FP (AFP-L3) reportedly enhance the detectability of small HCC. The use of CT and MRI scans with contrast media can achieve a higher diagnostic accuracy than US. However, it must be taken into account that there use is costly (Omata, et al 2010).
4.4 Gray Scale Imaging
2-D grey scale US is the basic and the most essential first step examination for the diagnosis of HCC. For a number of years, tissue harmonic imaging’s (THI) have been used as an optional tool for grey scale imaging (Maruyama & Ebara, 2006).This is because THI improves both lateral and contrast resolution, as it narrows the width of the US beam; together with the reduction of echo and side lobe artifacts, the margin and the structure of the tumour nodule becomes clearer, with distinct delineation (Harvey, 2001).
At present, THI plays a major role in the regular work of grey scale US examination. Advances in transducer performance are also important for improving the diagnostic ability of US. Recent digital technologies have provided control of the broad-frequency band, improved penetration and signal-to-noise-ratio, and increased spatial and contrast resolution; all such features help to raise the imaging qualities of sonograms. However, a small lightweight transducer is now desirable due to the increasing population worldwide of elderly people ( Maruyama.H &Ebara, M. 2006).
4.5 Contrast Enhanced Sonography
Contrast-enhanced ultrasound (CEUS) is a dynamic real-time examination performed with intravascular microbubble contrast agents. It shows lesional and liver enhancement analogous to that shown on contrast-enhanced CT or magnetic resonance (MR) scan (Wilson, &Burns, 2006).
The recent development of microbubble contrast agents has changed the role of US in the evaluation of cirrhotic patients. According to Nicolau et al (2004), US can be used not only for the detection of HCC s and FLLs but it is also valuable for the evaluation of vascular blood supplies of these lesions. The first ever studies using US contrast agents were performed with Doppler (spectral and colour) in the attempt to improve the visualisation of the vascular structure and identify vessels smaller in size with slower flow than were detectable with unenhanced Doppler.
According to Francanzani et al (2001) the use of first generation contrast agents demonstrated a significant improvement in the depiction of the blood flow of HCCs using colour Doppler modalities, and found intratumoral blood flow in 95% of HCCs after the administration of contrast agent. In contrast to this Vilana et al (2003) detected intratumoral arterial vascularity in 87% of HCCs before and 100% of HCCs after the administration of contrast agent.
However, the use of contrast agents associated with Doppler US causes poor signal resolution from the microbubbles, as they cannot depict the tumour’s microvasculature. In addition, the high transmit power used with colour Doppler causes rapid destruction of the microbubbles producing blooming artefacts, preventing clear evaluation of the microvascularisation and the different phases of the contrast dynamics. Another limitation in the use of colour Doppler contrast is its high susceptibility to tissue motion artefacts (Nicolau, et al 2004).
New technologies such as phase or pulse inversion harmonic imaging have been developed to improve the detectability of the microbubble signals, while specific US software is now able to detect the non-linear responses of the microbubbles and at the same time suppressing the linear signals from the tissue. The combination of second generation CEUS with microbubble techniques using low transmit power provides high-quality, detailed information of blood supply of an FLL similar to that of helical CT or MRI (Gaiani et al 2004).
This combination demonstrates many advantages over CT, such as real-time evaluation, no ionising radiation exposure, the avoidance of iodinated contrast agents, and a possible reduction in the waiting time to achieve the final diagnosis.
According to Maruyama, & Ebara, (2006) it has been ongoing challenge to establish contrast-enhanced US with microbubble agents. While free gas bubbles are efficient scatters of US, their utility has been limited due to their removal by the lungs.
Although colloidal suspensions and emulsions were developed, in the 1980s, for stabilized US contrast agents, their practical use was compromised by difficulties in the controlling of the size of bubbles and in attaining stabilisation of the contrast effects (Maruyama, & Ebara, 2006). However, in the late 1980-1990s, the grey scale CEUS, with the use of carbon dioxide gained a broad appreciation as an echo-enhancing technique, with high sensitivity for detecting tumour vascularity and high performance for the characterisation of liver tumours; however, the method requires arteriography procedure, because carbon dioxide is easily soluble in the blood (Maruyama, et al 2004).
According to the blood supply of the liver, three contrast phases are applied in succession; the arterial, portal and late phase shown in Figure 5, ending with the disappearance of the microbubbles about five minutes post injection (Cokkinos et al 2007). It is believed by Rettenbacher (2007) that the above phenomenon is attributed to the uptake of the microbubbles in the liver cells. As a consequence of this additional retention, the entire liver volume may be scanned for several minutes following a single dose of contrast agent.
The safety of CEUS has been studied extensively. It has been found to be generally safe, not nephrotoxic, and the incidence of hypersensitivity or allergic reactions appear much lower than CT or MRI contrast (Rettenbacher, 2007).
With CEUS, HCCs are characterised by hypervascularity in the arterial phase. Using real time evaluation with low MI, early and usually intense arterial enhancement is identified and in most cases the feeding artery is clearly identified. Tumour vessels usually appear with a basket like structure extending from the periphery to the centre of tumour (Nicolau, 2004) Figure 6.
Fig 6 a-d Hepatocellular carcinoma in a 75-year-old woman. a On baseline US, an echo-poor lesion was detected in the right liver lobe. b Dynamic CEUS using CPS and SonoVue with a low MI (<0.2). The early arterial phase at 24 s showed peripheral tumoural vessels with enhancement filling from the periphery to
the centre. c The arterial phase at 28 s showed homogeneous tumoural enhancement except for a small echo-poor area. d In the portal phase the HCC became iso-echoic with respect to the surrounding liver with the small non-enhancing area that was clearly demonstrated (Nicolau, (2004)
Recent studies by Wilson, & Burns, (2006) demonstrated that CEUS had a positive predictive value of 90% in diagnosing HCC. However, more recently US elastography has been introduced as a new technique for the evaluation of the elastic property (stiffness) of tissue and according to Choi, & Lee, (2010) it shows promise in discriminating malignant from benign lesions and improving conspicuity of malignant nodules.
Many microbubble contrast agents have been developed as summarised in Table 8.
Table 8 showing summery of US Contrast Agents (Maruyama,2006).
As mentioned above in table 8, there are many contrast agents on the market but most of them have not given a positive outcome; the results with Albunex and Echovist have had a disappointing outcome, after being injected via the peripheral route, as they did not provide sufficient enhancement in the left ventricle, aorta, and abdominal organs due to their instability (Goldberg, 1997). At the end of the twentieth century, a glactose based agent was introduced Lovovist. This agent was long awaited, according to Maruyama, (2006), and was said to provide a stable improvement in abdominal organs with a peripheral injection. Adding to this a current literature concludes that Sonazoid, which is a new second generation US contrast agent , provides detailed perfusion features of the tumour during the vascular phase, as well as Kupffer imaging in the post vascular phase (Hatanaka, 2008). However, both Lovovist and Sonazoid mount up in the liver, and sonograms in this phase are frequently used for the detection or characterisation of liver tumours.
In contrast, Definity and Sono Vue which are popular in European countries including UK do not accumulate in the liver (Lim, et al 2004). SonoVue is a second generation contrast agent that contains phospholipid stabilised microbubbles filled with sulphur hexafluoride, with a diameter of less than 8µm. These microbubbles circulate in the blood vessels, crossing the pulmonary and systemic capillary circulation. SonoVue shows characteristic oscillation behaviour under very low mechanical index (MI), and can reduce the signals derived from tissue and microbubble breakdown. As a result of this, contrast harmonic imaging under low MI level has received considerable attention for the real time observation of microbubble images, and it is expected to improve in the near future to diagnose liver tumours (Greis, 2004).
It is believed according to Soye et al (2007) in the future, contrast materials will be a routine component of ultrasound as well as with other imaging modalities such as CT and MRI, rather than a special option.
4.6 Computed Tomography
The ability of CT to detect and characterise liver lesions has been one of the most studied and evolving issues in radiology over the past twenty years (Zech, 2009). Technological advances, combined with increased knowledge about the pathophysiology of these tumours and the liver has resulted in dramatically increased abilities to detect and characterise HCC, imaging large or small lesions remain a difficult task despite what other authors claim (Baron, 2004).
CT is the most commonly used imaging modality in the diagnosis of HCC, made easily available and having short examination time. Multiphasic helical CT (MPCT) is considered the imaging technique of choice for the detection and staging of HCC (Yu, 2004).
MPCT consists of four phases; pre-contrast hepatic arterial (HAP), portal venous (PVP) and delayed phase (DP). In the MPCT, a high speed single detector spiral scanner is used to obtain images. Images are achieved after contrast injections at a delay of 25s HAP, 70s PVP, and 300s DP. HCC appear as hypervascular during the HAP; owing to the fact the hepatic artery grants the main blood supply, and appears rather hypodense during DP, which is recognised to the early wash out of contrast. However, in the DP images can assist in the diagnosis of HCC in 14% of patients (Khan, 2009).
The diagnostic accuracy of CT is affected by technical factors, such as contrast injections, and intrinsic factors related to the tumour, such as tumour size and vascularity (Franca, 2004). The sensitivity of the four phase CT in identifying HCC was up to 100% for tumour greater than 2cm in size, it showed 93% of tumours being1-2 cm in size and 60% of tumours less than 1 cm in size,(Khan, 2009).
Bruix, et al (2001) concludes that spiral CT is the standard imaging technique for the detection of response to loco-regional treatment of HCC. However, Colagrande, et al, (2003) elaborates further, that it is more effective than merging US scanning and ?FP level in the recognition of early HCC recurrence after successful treatment. A more recent study by Dai, (2008) evaluates the diagnostic efficacy of CECT and CEUS in patients with small hepatic nodules. This gave the CEUS a diagnostic value of 89.3%, for sensitivity 91.1%, and specificity 87.2%. For the CECT the diagnostic accuracy came to 88.4%, sensitivity 80.4% and specificity 97.9%. This shows no significant distinction between CEUS and CECT in characterising small (1-2 cm) hepatic nodules.
A study by Zech, et al., (2009) concludes that multidetector CT (MDCT ) technology has outstandingly improved the performance of CT in liver imaging. The ideal imaging temporal window for the detection of HCC using an extracellular fluid agent is very short approximately10s, whereas dynamic liver imaging requires high temporal and spatial resolution.
MDCT provides substantial improvement in temporal resolution from 25s for single spiral CT technology to <3-10s for MDCT and also in spatial resolution isotropic or near isotropic voxel dimension (Lencioni, et al., 2005). MDCT allows collection of early (18-28s after injection of contrast) and early parenchymal (35-45 s) arterial phase images. The early arterial images demonstrate vessels most favourably needed for treatment planning in patients who are likely to go through surgery, while the late arterial phase images illustrate the lesion better than the early arterial phase (Baron, 2004). Evaluation of both late and early phase images allows better results in sensitivity and positive predictive values, but MDCT with two arterial phases hold the risk of increased radiation exposure therefore limiting its use (Saar, & Kellner-Weldon, 2008). MDCT has shown to have elevated sensitivity in the detection of HCC in cirrhotic liver, due to the high speed and flexibility primary to the achievement of high quality thin section imaging and 3D capabilities (Bailecki, 2005).
The latest development in CT applications for liver imaging is volume perfusion imaging. Perfusion CT provides quantitative data regarding perfusion parameters, which might differentiate diverse tumour tissues based on perfusion behaviour and as a result, can enhance the ability to monitor therapy and grade tumours. HCC has also been reported to show high perfusion values (high blood flow, blood volume, and permeability and low mean transit time) compared to the normal tissue according to (Sahani, et al., 2007). In addition CT perfusion reveals that HCC has reduced blood flow, blood volume and permeability after antiangiogenic treatment or chemoembolisation, but the current problem is high radiation dose (Zhu, et al 2008).
On contrast enhanced CT (CECT) MDCT, the typical HCC demonstrates similar improved patterns to those seen on CEUS, with powerful inhomogeneous enhancement seen in the hepatic arterial – dominant phase and contrast wash-out in the late portal venous phase (Khan, 2009) Figure 7.
Figure 7 HCC Contrast enhanced CT demonstrates heterogeneous arterial phase enhancement of a focal liver lesion (red arrow) adjacent to a low attenuation area representing a previous radiofrequency ablation site (white arrowhead) (Khan, 2009)
It was reported the study conducted by Zhoa,(2007) that MDCT scanning was helpful in early detection and the effective treatment of small HCCs. In particular, the study found this to be the case during follow –up process of patients with chronic hepatitis and cirrhosis. The study compared the efficacy of gadolinium-enhanced multiphase dynamic MRI with MDCT scanning for the detection of small HCCs. The study found the detection rate of small HCCs on MDCT to be 97.5%-97.6% and 90.7%-94.7% on MRI according to tumour size. For very small HCCs of ? 1cm, the sensitivity of detection on MDCT was higher compared to MRI (90.0%-95.0% and 70.0%-85.0% respectively).
The authors conclude that MDCT scanning was better than MRI in the early detection of small HCCs during the follow-up of patients with chronic hepatitis and cirrhosis (Zhoa, 2007).
4.7 Magnetic Resonance Imaging
MRI is superior to CT and US in detecting and characterising HCC in the cirrhotic liver (Takayama, et al., 2008 ). According to Takayama, et al., a recent advance in MRI software and hardware, including the use of parallel imaging and surface phased array coils, provide faster sequences that can be acquired within a breath-hold, decreasing motion and respiratory artefacts. The use of intravenous contrast material with multiphasic imaging is vital to identify and characterise focal hepatic lesions (Takayama, et al., 2008).
Although MRI is often termed as the most sensitive and detailed technique for evaluating the liver, this can be debatable, given the recent revolution in MDCT technology (Glockner, 2007). On the other hand, lesion/liver distinction is higher for MRI than that with CT and the flexibility, range of pulse sequences are available in MRI providing a considerable advantage over CT (Khan, 2009). Most examinations in MRI include a T1 – weighted in-phase/out-of-phase spoiled gradient echo sequence and one or more T2 – weighted sequences. A small HCC is defined by a size < 2 cm. Small HCCs have a uneven appearance on T1 –weighted images. On T2 – weighted images, HCCs are classified as hyperintense. However, well differentiated HCC lesions can be iso- intense on T2 –weighted images, both the hypo-tense or iso-intense is highly suggestive of an HCC developing within dysplastic nodule (DN)(Takayama, et al., 2008).
Combining T1 and T2 – weighted sequences with extracellular intravenous contrast agents, usually fat saturated spoiled gradient echo sequence, allows the patterns of tumour enhancement to be determined (Khan, 2009)
According to Kim,(2004) the use of super-paramagnetic iron oxide (SPOI)-enhanced MRI or manganese dipyrid-oxal diphosphate – enhanced MRI is less efficient than Gd- enhanced dynamic MRI in the detection and characterisation of HCC. However, Gandhi,(2006) states that the use of tissue-specific contrast agents such as super-paramagnetic iron oxide,(SPOI) permits enhanced detection and classification of liver tumours. Contraindications to MRI are pacemakers, implantable cardiac defibrillators, cochlear implants and metallic orbital foreign bodies (Choi,& Lee, 2010 ).
HCC obtain its blood supply almost from the hepatic artery most HCCs are best seen on arterial phase images. This allows differentiation from regenerative nodules (RNs) and DNs, which are not hyperintense during the arterial phase (Takayama, 2008). Khan, (2009) echoes this statement, commenting that HCC can have an uneven look on unenhanced T1– weighted images and characteristically shows increased signals on T2– weighted images shown in Figure 8.
Figure 8 HCC. T2-weighted gradient echo sequence shows a solid lesion in segment V (arrow) of the liver which is of intermediate signal hyperintensity compared to the surrounding liver parenchyma
In the administration of gadolinium, HCC demonstrates distinguishing early enhancement on arterial phase imaging and washout on the delayed images- resulting in a hypointense lesion in contrast to the surrounding parenchyma shown in Figure 9 (a) and (b)
Figure 9 A: T1-weighted fat-suppressed sequence following gadolinium intravenous injection shows arterial phase enhancement of a focal liver lesion in segment IV (red arrow);
Figure 9 B: The same lesion as shown in Figure 9A becomes relatively less conspicuous on the portal phase images (red arrow) as the surrounding liver parenchyma begins to enhance.
Another new MR technique which is apparently promising for the diagnosis of HCC is diffusion-weighted imaging (DWI) (Zech, 2009). This technique is based on intravoxel incoherent motion and provides insight into the molecular water composition and the degree of tumour viability at the cellular level (Zech, 2009).
DWI is said to differentiate malignant nodule from benign liver lesions, and to monitor the treatment response after chemoembolisation and allowing an increasing detection rate for HCC with gadolinium enhanced MR in the cirrhotic patient (Zech,2009). However, the technique shows no evidence in how far DWI might be a realistic approach to differentiate between RNs, DNs, and HCC. It may also aid in the detection and characterisation of FLLs. The liver parenchyma appears to be dark on DWI, whereas, liver tumours both benign and malignant are portrayed as high signal concentrated masses, although malignant liver tumours have lower apparent diffusion coefficients (ADCs) than benign cysts and haemangiomas (Khan, 2009).
The sensitivity of MRI in detecting HCC depends on tumour size (Zech, 2009). It is about 95% in tumours larger than 2 cm, while in tumours less than 2 cm the sensitivity is reduced to 30% (Zech, 2009). MRI is also very good at outlining the internal architecture of the tumour, the tumoral margins and intrahepatic vascular invasion (Khan, S.A.2009).
4.8 Positron Emitted Tomography
Positron emission tomography (PET) is different from other imaging modalities due to the use of radiopharmaceuticals whose accumulation is due to specific cellular mechanisms that characterise properties related to tumour activity. There are PET radiopharmaceuticals that evaluate the tumour blood flow, glucose metabolism, protein synthesis, proliferation, apoptosis, hypoxia, and the presence of specific receptors (Hellman, 2006).
The first PET scan was reported in the 1980s and since then, their use in both research and practical applications have rapidly expanded (Sun, et al 2007). The most widely available PET radiopharmaceutical is 18F-fluorodeoxyglucose (FDG), this is a glucose analogue that accumulates in regions of hypermetabolic activity. After intra-cellular transportation and phosphorylation, 18F-FDG is locked within the cell as unlike glucose it is unable to undergo further metabolism (Garcea, et al., 2009)
The combination of conventional cross-sectional imaging with PET scanning enables both functional and anatomical information regarding a patient to be fused into one study (Sun et al., 2007). With PET images on its own, it may not be possible to accurately localise an area of increased activity as a result of the absence of identifiable anatomical structures. With the CT scan, the intensity of the images seen correlates with the structure and visceral density of the examined organ. However, in PET/CT the image intensity is dependent on the functional activity of the tissue taking up the radiotracer (Garcea, 2009).
Shin et al., (2006) state that several radiotracers are available and have been used in the detection of HCC using PET/CT, which provides an insight into their physiological features, including glucose consumption assessed with 18F-FDG and lipid synthesis (11C-acetate), cell membrane metabolism and tumour proliferation ( 18F-fluorocholine).
However, in PET/CT investigation only 30-50% of primary HCC demonstrate 18F-FDG up take above background levels. High levels of glucose-6-phosphatase are found in normal liver and HCCs leading to dephosphorylation of 18F-FDG, which subsequently no longer accumulates in cells and redistributes back into the circulation. For this reason, PET-CT has limited application in the evaluation of intra-hepatic HCCs (Garcea, 2009).
Recently, the radiopharmaceutical 11 C-acetate was tried to overcome the low sensitivity of 18F-FDG PET/CT for detection of HCCs. (Ho, et al., 2007)
Ho, et al., (2007) showed in his study that with less than three HCC lesions,11C-acetate PET detected 87.3% of the tumours whereas 18 F-FDG PET/CT detected 47.3%. However, Talbot, et al., (2006) concludes that the use of 11 C-acetate is limited to PET centres which have on-site cyclotrons due to its short half-life approximately twenty minutes. This disadvantage has prompted the development of other radiotracers such as the 18 F-fluorocholine (FCH) which have longer half-life of 110 minutes.
18 F-FCH is more readily available than 11 C-acetate in PET centres according to Talbot, et al., (2006) and it permits delayed imaging, which is useful in to obtain improved signal to noise ratios, permitting wash-out from non-specific sites of uptake. One must take into account that this study was only carried out in patients with suspicious liver masses or suspicion of HCC recurrence, and that too few studies have been performed, therefore a larger number of series are required in the future to confirm these initial findings.
4.9 Angiography
According to Yu, et al., (2004) most HCCs are hypervascular. The arterial feeders to the tumour are often dilated, tortuous, distorted and displaced. Neovasculatures show a muddled and disorganized pattern. There is often a strong tumour stain. Vascular lakes or venous pools are common as shown in Figure 10.It is thought that the diagnostic effectiveness of hepatic arteriography is related to tumour size and vascularisation (Khan, 2009 ). However, some tumours are only placidly hypervascular with mild tumour staining that can only be demonstrated in a good quality discriminatory arteriogram. Central necrosis is not uncommon in large hypervascular tumours, and it is represented angiographically by a hypervascular area. Invasion of the portal trunk and its major branches is not uncommon in HCC (Yu, et al., 2004).The “thread and streaks” appearance seen in hepatic arteriogram is due to tumour invasion of the vasa vasorum of the portal vein (Yu, et al., 2004) Figure 11.
Fig 10. Arteriography showing dilated, tortuous and displaced arterial tumour feeders with Neovasculatures showing a chaotic and disorganised pattern. Vascular lakes are present (Yu, 2004)
Fig 11.Tumour invasion of a right hepatic vein on hepatic angiogram. Note the “thread and streaks” sign. (Yu, 2004)
The use of angiography in the detection of HCCs smaller than 5cm is reported that the sensitivity, specificity and diagnostic analysis falls in the value of 82%-93%, and 735-89% respectively. Currently, angiography is used to outline hepatic structure before resection or as management for transarterial chemoembolisation of HCC lesions (Bialecki, 2005)
CHAPTER 5 HEPATOCELLULAR CARCINOMA5.1 Treatment of HCC
Hepatic resection, radiofrequency ablation (RFA), and liver transplantation are accepted as an effective treatment for HCC (Takayama, 2008).
Resection is the most favoured treatment for HCC in non-cirrhotic patients, who account for about 5% of the cases in Western countries (Lencioni, 2005). However, patients with cirrhosis, the choice of resection has to be carefully considered due to the risk of postoperative liver failure (Crocetti, 2008). It has been shown in the Crocetti, (2008) study that having both normal bilirubin concentration, absence of clinically significant portal hypertension, gave an excellent outcomes after surgery, and it may achieve a 5-year survival higher than 70%.
Liver transplantation is the only option that provides a cure for both the tumour and the underlying chronic liver disease (Llovet, 2003). Liver transplantation is recognised as the best treatment for patients with a solitary HCC smaller than 5 cm in the setting of final stage of cirrhosis and for those with early multi focal disease (up to 3 lesions, no more than 3cm), (Llovet, 2003). Crocetti, (2008) concludes that patients that underwent transplantation were better than those patients that were submitted to resection, especially if the significantly lower rates of tumour recurrence are less than 10-20% versus more than 70% at five years.
Image guided percutaneous ablation is currently accepted as the best therapeutic choice for non surgical patients with early stage HCC (Bruix, 2005). Over the past two decades, several methods for chemical ablation or thermal tumour obliteration have been developed and clinically tested. These include the injection of ethanol or acetic acid, microwave coagulation, and the administration of localised heating or freezing (radiofrequency ablation) (Crocetti, 2008).
The influential technique used for local ablation of HCC is percutaneous ethanol injection (PEI). Ethanol persuades coagulation necrosis of the lesion as a result of cellular dehydration, protein denaturation, and chemical occlusion of small tumour vessels. PEI is a well-established technique for the treatment of nodular-type HCC. HCC nodules have a soft consistency and are surrounded by a firm cirrhotic liver. Subsequently, injected ethanol disperses within them easily and selectively, leading to complete necrosis of about 70% of small lesions. Although several retrospective studies have provided indirect evidence that PEI improves the natural history of HCC (Koda, 2000).
The disadvantage of PEI is the high local recurrence rate, which may reach 33% in lesions smaller than 3 cm and 43% in lesions exceeding 3 cm. The injected ethanol does not always achieve complete tumour necrosis because of its inhomogeneous allocation within the lesion especially in the presence of intratumoral septa and the limited effect on extracapsular cancerous spread (Omata, et al., 2010). Moreover, PEI is unable to create a safety margin of ablation in the liver parenchyma surrounding the nodule, and therefore may not destroy tiny satellite lesions that even in small tumours may be located in close proximity to the main nodule (Crocetti, 2008).
Radiofrequency ablation (RFA) is used to encourage thermal injury to the tissue through electromagnetic energy deposition. RFA imaging techniques such as US, MRI and CT are used to help guide the needle electrode into the specific site of tumour. High frequency electrical currents are then passed through the electrode, creating heat that destroys the abnormal cells. RF ablation has been the most broadly assessed alternative to PEI for local ablation of HCC (Lencioni, 2005).
Historical data from explanted liver specimens in patients who underwent RFA showed that tumour size and the presence of large (3mm or more) adjacent to vessels significantly affect the local treatment effect (Omata, et al.,2010). Complete tumour necrosis was pathologically shown in 83% of tumours less than 3 cm and 88% of tumours in a non-perivascular location (Lu,2005).
Randomised control trials (RCT) have proved that RFA is superior to PEI in the treatment of small HCCs in terms of treatment response, recurrence, and overall survival rates, while some literature report that RFA have higher complication rates ( Omata, et al., 2010).
The RCT established that the amount of treatment sessions was reduced with RFA than that with microwave coagulation. Moreover, in RFA the survival rates were reported to be 39.9-68.5% at 5 year (Yan, 2008). The local tumour progression rates to be 2.4-16.9% and mortality, morbidity rates of RFA reported to be 0.9-7.9% and 0-1.5% respectively (Cheng, 2008).
Chapter 6 Hepatocellular Carcinoma6.1 Conclusion and Future Recommendation
The prevalence of HCC is increasing around the world. It is estimated 610,000 lives will decrease from HCC worldwide, this figure is set to increase year by year.
Imaging analysis of HCC remains difficult, and correct diagnostic confirmation and careful staging of patients with HCC is crucial to establish prognosis and plan appropriate treatment. The current imaging modalities such as CEUS, MRI and CT, have a high sensitivity and positive predictive values in diagnosing obvious HCC, but they are less sensitive for detecting early HCC and fail to spot tumours that are 2cm or are well differentiated.
Ultrasound has dramatically improved in the recent years, and continues to be the most used imaging modality for the screening of HCC. The development of US system and its application of CEUS, US are more likely to play a leading role in the diagnosis and treatment of HCC. However, the improvement in US devices, with the use of contrast agents shows an increase in sensitivity and accuracy in evaluating the haemodynamics of HCC. It also shows that using low mechanical index contrast-specific US techniques can reduce the signals coming from tissue and microbubble breakdown.
Microbubble contrast agents have dramatically changed the role of US in the evaluation of cirrhotic patients, not only can US be used for the detection of HCCs and FLLs but also allows the evaluation of vascular blood supplies. CEUS is found to be safe, not nephrotoxic, hypersensitivity and allergic reactions are much lower than CT or MRI contrast.
The advent of MDCT in recent years has dramatically improved the ability to detect and stage HCC, providing sensitivities similar to CEUS. However, limitations do include; these being inherent radiation dose and a low sensitivity for characterising tumours smaller than 2cm in diameter. Advances in MRI technology and development of liver-specific contrast agents have greatly improved the accuracy in HCC evaluation, and is now emerging as the modality of choice in this field. MRI is superior to CT in sensitivity and specificity and therefore should be utilised where CT is ambiguous or non-contributory.
The main characteristic in the development of HCC is neovascularisation and complete response to treatment is defined by the elimination of enhancement in the arterial phase. However, follow-up CT or MRI is the most commonly used techniques for assessing treatment efficacy. This is because they are able to detect residual viable tumour. In patients with poor liver function, multifocal tumours or associated diseases, surgical resection of HCC is not an option and, in cases, non-surgical therapy such as PEI, PMC or RFA may be applied.
The combination of conventional cross-sectional imaging with PET scanning enables both functional and anatomical information regarding a patient to be fused into one study. With PET on its own, it may not be possible to accurately localise an area of increased activity as a result of the absence of identifiable anatomical structures.
Future evaluation of radiological tests for the detection of HCC in cirrhotic patients should focus on the detection and characterisation of tumours smaller than 2 cm in size. The optimal imaging parameters and contrast injection protocols for lesion detection should be defined.
Therefore it clearly shows that, CEUS using second generation contrast agents and specific is a very useful tool in the characterisation of FLLs detected by US in cirrhotic patients, allowing the differential diagnosis between HCC and other FLLs. CEUS may also help in the staging of HCC and in the management of patients with HCC treated percutaneously.
Both MDCT and MRI have reached high standards for the detection of HCC with the possibility of multiphasic examinations, high resolution imaging and functional capabilities.
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