Differential Diagnosis

The advantages of SPIO-enhanced MR imaging have also been reported in tissue characterization. Some types of hepatic lesions such as focal nodular hyperplasia (FNH), hepatocellular adenoma, dysplastic nodules (DN), and well-differentiated HCC sustain phagocytic activity and may demonstrate iron oxide uptake (Grandin et al., 1995; Vogl et al., 1996). Sustained phagocytic activity is a feature of FNH, and is helpful in differential diagnosis with SPIO-enhanced MR imaging (Grandin et al., 1995; Vogl et al., 1996) (Figure 4.6). One criterion, of a threshold signal loss of 10% on SPIO-enhanced MR images, has been established to distinguish benign from malignant lesions (sensitivity 88%, specificity 89%) by receiver-operating characteristic analysis (Vogl et al., 1996). Successful differentiation between HCC and DN is clearly of great importance for the early

Figure 4.6. Focal nodular hyperplasia in a 34-year-old male. In the arterial phase of dynamic MR imaging, a well-enhanced tumor is noted in S7 (a, arrow). Pre-contrast T2W-FSE reveals a high-intensity mass (b, arrow). On SPIO-enhanced T2W-FSE, the tumor takes up SPIO and its signal intensity is decreased (c).

Figure 4.6. Focal nodular hyperplasia in a 34-year-old male. In the arterial phase of dynamic MR imaging, a well-enhanced tumor is noted in S7 (a, arrow). Pre-contrast T2W-FSE reveals a high-intensity mass (b, arrow). On SPIO-enhanced T2W-FSE, the tumor takes up SPIO and its signal intensity is decreased (c).

and precise treatment of HCC in cirrhotic liver. One study found no significant difference in the number of Kupffer cells between well-differentiated HCC and surrounding liver tissue (Tanaka et al., 1996). It should thus be noted that phago-cytic activity might overlap among borderline lesions. Another study reported that the ratio of the intensity of tumorous lesion to that of non-tumorous areas on SPIO-enhanced MR images (SPIO intensity ratio) correlated inversely with the Kupffer-cell-count ratio in HCCs and dysplastic nodules and increased as the degree of differentiation of HCCs decreased (Imai et al., 2000). This indicates that the uptake of SPIO in HCCs decreased as the degree of differentiation of HCCs declined.

We found that some well-differentiated HCCs exhibited signal decrease similar to the surrounding liver on T2W-FSE images, but less signal decrease than surrounding liver on T2W-GRE images (Table 4.3) (Tanimoto, 2006). Conversely, DNs exhibited strong decrease in signal on both T2W and T2*W images (Figure 4.7). This finding could be explained by the fact that magnetic susceptibility effects in T2*W-GRE imaging depends on the intracellular SPIO cluster size (Tanimoto et al., 2001). In well-differentiated HCCs, Kupffer cell density would be maintained but Kupffer cell function reduced compared to

Table 4.3. Contrast patterns on T2W and T2*W imaging of borderline lesions.

Rank

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