Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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enhanced MRI appears superior (Fig. 7.33). Such comparisons are difficult to place in a wider clinical perspective; they reflect specific MR units used and specific imaging conditions. The SPIO-enhanced hepatocellular carcinomas appear slightly bigger than on comparable gadolinium-enhanced images.

A 3D MRA rotational display, obtained from 2D TOF images using SPIO, shows their rela-

tionship to portal and hepatic veins on the same image, information useful during presurgical planning.

Chondroitin sulfate iron colloid is a potential intravenous MR contrast agent. The tumor-to- liver contrast-to-noise ratio is significantly increased after chondroitin administration, primarily in moderately to poorly differentiated hepatocellular carcinomas.

Well-differentiated hepatocellular carcinomas exhibit considerably more uptake of MnDPDP than poorly differentiated ones and as a result these tumors can range from hyperto hypointense; those that become isointense are not detected with this contrast agent. In overall hepatocellular carcinoma detection Mn-DPDP appears inferior to gadolinium (108). This agent does not aid in differentiating these tumors from adenomas and focal nodular hyperplasia but does help in differentiating hepatocellular carcinomas from metastases (the latter exhibit little uptake).

Will combined use of SPIO followed by injection of a gadolinium contrast agent (called double-contrast MRI by some) aid carcinoma detection? Such a double-contrast study in cirrhotic patients with suspected hepatocellular carcinoma revealed that SPIO-enhanced MRI was more accurate than precontrast MRI, and double-contrast MRI was more accurate than SPIO-enhanced MRI (109). Such double MR studies are especially useful in characterizing nodules in a cirrhotic liver (110).

Scintigraphy

Some hepatocellular carcinomas have Tc-99m- IDA uptake. A not uncommon pattern is to see little or no uptake within the first hour, with the lesion subsequently filling in. In general, welldifferentiated carcinomas show uptake while less differentiated ones appear cold.

Hepatocellular carcinomas show variable gallium 67 citrate uptake, a nonspecific finding; abscesses and some metastases also reveal uptake; however, in the appropriate setting such uptake should suggest a hepatocellular carcinoma.

Uptake of Tc-99m-methoxyisobutylisonitrile (MIBI) using SPECT is variable and appears related to tumor histology.

Although thallium 201 chloride is a promising tumor imaging agent, its use in the liver is limited by normal liver uptake. When sequentially combined with Tc-99m–sulfur colloid, SPECT Tl-201 images show increased activity in hepatocellular carcinomas while Tc-99m–sulfur colloid SPECT reveals photopenia at these sites.

Some neoplasms have increased FDG metabolism, and PET-FDG is useful in their detection. Most hepatocellular carcinomas have increased uptake, but a minority have uptake equal to liver

ADVANCED IMAGING OF THE ABDOMEN

and thus are not detected. FDG metabolism does not necessarily correlate with tumor differentiation. Adenomas and fibronodular hyperplasia have poor uptake.

Biopsy

A need to establish pathologic diagnosis is obvious with a suspected tumor. Percutaneous biopsy using imaging guidance usually is diagnostic. If aggressive therapy of confirmed hepatocellular carcinoma nodules is planned, knowledge of the histologic subtype may suggest a specific therapy. Thus early or sclerosing carcinomas with their limited tumor vascularity do not respond to arterial embolization. Early carcinomas tend to respond to percutaneous ethanol injection, while sclerosing types respond poorly.

Both cytology and histology can be used to diagnose these tumors. Biopsies are often performed in cirrhotic livers and results are superior when cytology and histology are combined. In general, a diagnosis can be obtained in about 90% of tumors when using an 18 gauge cutting needle and US guidance. Biopsy appears safe provided the interposing liver parenchyma is >1cm. Postbiopsy bleeding is a recognized complication.

One biopsy complication is an intrahepatic arterioportal fistula. Postbiopsy (with a 14gauge Thru-Cut needle) arterioportal fistulas detected by DSA can be treated with coil embolization and followed by planned chemoembolization.

Tumor spread along a needle tract after fineneedle biopsy of a hepatocellular carcinoma appears rare, with only occasional reports published.

Staging

The TNM hepatocellular carcinoma staging classification is outlined in Table 7.12. Some investigators also use a Stage 0—defined as a solitary hepatocellular carcinoma <2cm in size in patients with compensated cirrhosis. Stage 0 is a useful concept in patients undergoing various percutaneous ablation therapies. In general, staging of these tumors is less useful than with most cancers because underlying liver function plays a major role in patient survival. Direct spread to adjacent structures is a

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Table 7.12. Tumor, node, metastasis (TNM) staging of liver cancer

Source: From the AJCC Cancer Staging Manual, 6th edition (2002), published by Springer-Verlag, New York, NY, used with permission of the American Joint Committee on Cancer (AJCC), Chicago, IL.

common late finding. For example, direct invasion of the proximal transverse colon, mucosal erosion, and exsanguination are not uncommon.

Iodized oil-CT is often used as an imaging gold standard to detect additional carcinoma nodules. Its limitation has already been mentioned.

Ultrasound angiography using small CO2 bubbles appears to aid in staging and planning therapy. Comparing helium and CO2 bubbles injected into proper hepatic artery in patients with hepatocellular carcinoma, enhancement duration is longer with helium than with CO2 and the degree of enhancement greater (111); helium aids in additional carcinoma nodule detection.

Hepatocellular carcinoma has a predilection for vascular invasion (Fig. 7.34). Most common is spread to the portal vein, although inferior vena caval involvement is not uncommon, an occasional one even extending intraatrially. Normally, the portal vein enhances on postcontrast MRI portal venous phase images; with invasion, the portal vein contains an intraluminal nonenhancing tumor rather than contrastenhancing blood, although some tumor thrombi show early arterial enhancement during dual-phase CT, thus suggesting a diagnosis. The etiology of portal vein thrombosis detected in patients with a known hepatocellular carcinoma is of obvious staging importance. Not all thromboses are neoplastic in origin; the superimposed cirrhosis present in many of these patients is also associated with portal vein thrombosis. A US-guided needle biopsy of the thrombus is a viable staging technique.

Although some authors believe that metastatic hepatocellular carcinoma is rare, tumor

spread outside the liver is not uncommon, mostly during advanced stages. Lymphatics, lung, and skeleton are typical sites; on the other hand, biliary tract involvement is uncommon. An incidental extrahepatic tumor in a patient with stage I or II intrahepatic hepatocellular carcinoma likely is not a metastatic focus.

The uncommon intraperitoneal drop metastases range from single to multiple, but are discrete. A rare metastatic hepatocellular carcinomas causes spinal cord compression.

Therapy

If applicable, resection is the preferred therapy for liver cancers. Several other modalities have evolved as therapies for unresectable hepatocellular carcinomas (Table 7.13). Some have had limited application, while others are currently in use, especially in those parts of the world where hepatocellular carcinoma is prevalent. Conventional chemotherapy and radiation therapy have a limited role. Based on a retrospective multicenter Japanese study of patients with hepatocellular carcinoma comparing resection, transcatheter arterial chemoembolization, and percutaneous transhepatic ethanol injection, the authors recommend either resection or ethanol injection for stage I tumors < or = 3 in number and < or = 30mm in size, ethanol injection for stage II tumors < or = 3 in number and < or = 30mm in size and resection (if applicable) for stage I tumors >31mm in size and

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regardless of number (113). Use of antiangiogenic agents to treat hepatocellular carcinomas is too new to draw any firm clinical conclusions.

Unresectable

The borderline between a resectable and an unresectable tumor varies between surgeons. Also, some hepatocellular carcinomas deemed unresectable are amenable to preoperative cytoreduction therapy to the point that it is subsequently resectable. In fact, an argument can be made that the primary role of preoperative therapy is to convert an unresectable hepatocellular carcinoma into a resectable one.

An occasional patient undergoes aggressive therapy and achieves prolonged survival even with an extensive hepatocellular carcinoma.

Resection

Preoperative localization of a focal liver lesions to a specific hepatic segment is of obvious interest to the surgeon, and therefore a need exists for imaging techniques to identify a segment in question. Two systems are in use for classifying liver lobes and segments: the Couinaud system, widely used throughout Europe and Asia, and an English system more common in Great Britain and United States (Table 7.14). The primary difference between the two systems is in nomenclature, with the Couinaud classifi-

cation dividing liver parenchyma into a left liver and a right liver, with each then being subdivided into sectors and segments. These segments are based primarily on portal vein subdivisions, their primary importance being in their anatomic use during surgical planning and resection.

Surgical resection continues to be the mainstay of therapy in patients without cirrhosis. A small solitary tumor is ideal for surgical resection. In such a setting absence of major vessel invasion or absence of intrahepatic metastases are factors affecting survival. Either a lobectomy, segmentectomy, wedge resection, or other type of resection is performed. Aggressive surgery is in vogue in some centers. A tumor thrombus in portal vein branches, hepatic veins, inferior vena cava, or bile ducts is not a contraindication to resection. In Japan, 5-year survival for patients with stage I hepatocellular carcinoma is about 70%, stage II is 50% and stage III is 30%. With recurrence, repeat surgery appears to prolong survival in some patients.

A small solitary tumor is ideal for surgical resection. In such a setting the absence of major vessel invasion or the absence of intrahepatic metastases is a factor affecting survival.

In a cirrhotic liver, postoperative residual liver function limits the extent of resection possible. Some surgeons are reluctant to perform a major hepatectomy in a setting of cirrhosis, although in some patients a partial hepatectomy

in such a setting has a mortality rate close to that in patients with a normal liver. A segmentectomy is effective for small hepatocellular carcinomas and can be safely performed even in a setting of chronic liver disease. Nevertheless, postoperative hepatic decompensation is a risk in cirrhotic patients, especially those with an increased preoperative portal pressure, and some surgeons restrict resection to patients without portal hypertension. Nevertheless, highly extended resection for advanced hepatocellular carcinoma with portal vein tumor thrombi is performed in some centers.

Preoperative portal vein embolization using a percutaneous transhepatic approach is feasible. Whether such embolization aids subsequent resection is debatable.

Laparoscopic hepatic resection is feasible for a hepatocellular carcinoma.

Extracorporeal resection has been tried in patients with an otherwise inoperable liver tumor. Whether ex-vivo MRI with its high spatial resolution aids such resection is not clear.

Transplantation

In a minority of patients transplantation is an option for hepatocellular carcinomas, treating both the carcinoma and any underlying liver disease. Typical candidates are patients who should be able to tolerate major surgery, should