Percutaneous Ethanol Injection PEI

Several studies have shown that PEI is an effective alternative to surgery in cases of small HCC. Tumor cell destruction is achieved by alcohol-induced immediate coagulative necrosis of the affected tissue as a consequence of protein denatu-ration and cellular dehydration [16].

The maximum diameter of HCC lesions that can be treated successfully by PEI is approximately 3 cm. Larger lesions are less amenable to treatment with this technique because the ethanol distributes less homogeneously, resulting in incomplete necrosis of the lesion. This applies equally for the treatment of liver metastases where PEI is of limited effectiveness for local tumor control [8].

T2-weighted MR images acquired post-PEI

typically demonstrate areas of markedly decreased signal intensity, corresponding to regions of ethanol-induced coagulative necrosis. The possibility of tumor recurrence should be considered if an area of increased signal intensity is observed within the lesion. However, in rare cases, necrosis with high signal intensity may be observed in the center of the lesion. This is indicative of liquefac-tive necrosis and should be borne in mind for differential diagnosis.

Contrast-enhanced Tl-weighted images in the equilibrium phase reveal a hypovascular area.

Recurrent or residual tumor should be considered if enhancement is detected within three to six months post-therapy (Fig. 10) [11, 17]. In cases of treated HCC, special attention should be paid to early enhancing areas in the arterial phase of the dynamic series of acquisitions since early enhancement is highly indicative of recurrent tumor.

On post interventional T1-weighted images a fan-shaped hypointense area of normal liver tissue adjacent to the treated HCC with a corresponding hyperintense signal on T2-weighted images can sometimes be observed and might be mistaken for residual tumor. This area, which typically enhances strongly on T1-weighted images after administration of contrast agent, represents pathologic changes in the normal liver tissue as a toxic reaction to the injected ethanol. Awareness of such abnormalities is important for the correct evaluation of therapeutic efficacy [29].

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