Hypovascular Metastases

Hypovascular metastases are the most frequent malignancies in the liver. In the United States, colon cancer is the most common primary site and approximately 50,000 cases of hepatic colorectal metastases are encountered annually.

Lesion detection is size-related, with lesions smaller than 1 cm being difficult to identify with conventional techniques. Unfortunately, a postmortem assessment of the size of liver metastases has shown that the ratio between metastases larger than 1 cm and those smaller than 1 cm is approximately 1:1.6 for metastases of colorectal adenocarcinoma and 1:4 for other liver metastases [4]. Therefore an ability to accurately detect and characterize metastases under 1 cm in size is clearly warranted in order to accurately detect and stage the tumor extent within the liver.

Hypovascular metastatic lesions tend to be round in shape although metastases larger than 3 cm from colorectal adenocarcinoma commonly have a cauliflower aspect. The SI of these metastases is lower than that of surrounding hepatic tissue on unenhanced T1-weighted images and typically moderately higher on T2-weighted images. A hypointense peripheral rim around tumor nodules may be seen on T2-weighted images in about 25% of colorectal hepatic metastases. The histopatho-logic changes associated with this rim include compression of hepatic parenchyma, hepatocellu-lar atrophy, fibrosis, inflammation, and congested sinusoids.

It remains a matter for debate whether the detection of hypovascular metastases is improved on contrast-enhanced images using conventional Gd agents compared to unenhanced images. On the other hand, even hypovascular tumors may show some enhancement that occasionally helps to detect or characterize the lesion. On hepatic arterial

Fig. 26a, b. Metastases from cholangiocellular carcinoma on unenhanced imaging. The pre-contrast T2-weighted image (a) reveals a round, well-defined, hyperintense lesion (arrow) in segment VI of the liver. On the corresponding pre-contrast gRe Tl-weighted image (b) the lesion (arrow) is homogeneously hypointense

Fig. 26a, b. Metastases from cholangiocellular carcinoma on unenhanced imaging. The pre-contrast T2-weighted image (a) reveals a round, well-defined, hyperintense lesion (arrow) in segment VI of the liver. On the corresponding pre-contrast gRe Tl-weighted image (b) the lesion (arrow) is homogeneously hypointense

Fig. 27a-e. Metastases from cholangiocellular carcinoma after Gd-BOPTA. Same case as Fig. 26. On the pre-contrast GRE Tl-weighted image (a) the lesion (arrow) is homogeneously hypointense. The nodule appears markedly hyperintense on the arterial phase image (b) after Gd-BOPTA administration. This hyperintensity persists into the portal venous phase (c). In the equilibrium phase (d) the lesion is isointense with a thin peripheral hypointense rim (arrowhead). In the hepatobiliary phase image (e) the nodule is homogeneously, markedly hypointense

Fig. 28a-f. Metastases from gastrointestinal stromal tumor (GIST) after Gd-EOB-DTPA. On the pre-contrast T2-weighted image (a), two round, well-defined, markedly hyperintense lesions (arrows) can be seen in segments IV and II of the liver. On the pre-contrast GRE Tl-weighted image (b) the nodules appear homogeneously hypointense. No enhancement is seen on arterial (c) and portal venous (d) phase images acquired during the dynamic series after Gd-EOB-DTPA administration, indicating large necrotic components within the lesions. In the hepatobiliary phase (e-f) 20 min after injection of contrast agent, the nodules appear isointense with a thin hypointense peripheral rim. This is due to non-specific intra-lesional pooling of the contrast agent in the necrotic components

Fig. 28a-f. Metastases from gastrointestinal stromal tumor (GIST) after Gd-EOB-DTPA. On the pre-contrast T2-weighted image (a), two round, well-defined, markedly hyperintense lesions (arrows) can be seen in segments IV and II of the liver. On the pre-contrast GRE Tl-weighted image (b) the nodules appear homogeneously hypointense. No enhancement is seen on arterial (c) and portal venous (d) phase images acquired during the dynamic series after Gd-EOB-DTPA administration, indicating large necrotic components within the lesions. In the hepatobiliary phase (e-f) 20 min after injection of contrast agent, the nodules appear isointense with a thin hypointense peripheral rim. This is due to non-specific intra-lesional pooling of the contrast agent in the necrotic components

Fig. 29a-d. Metastases from gastrointestinal stromal tumor (GIST) after Gd-BOPTA. Same case as Fig. 28. On the pre-contrast GRE Tl-weighted image (a) the nodules (arrows) appear homogeneously hypointense. In the arterial phase (b) of the dynamic series after Gd-BOP-TA administration the nodules appear hypointense and are surrounded by a hyperintense peripheral rim. Partial wash-out is apparent on the portal venous phase image (c). In the hepatobiliary phase (d) 1 h after contrast agent administration, the lesion located in segment IV of the liver appears slightly hypointense, due to non-specific intra-lesional pooling of the contrast agent in the necrotic components of the lesion. The lesion in segment II appears homogeneously hypointense

Fig. 29a-d. Metastases from gastrointestinal stromal tumor (GIST) after Gd-BOPTA. Same case as Fig. 28. On the pre-contrast GRE Tl-weighted image (a) the nodules (arrows) appear homogeneously hypointense. In the arterial phase (b) of the dynamic series after Gd-BOP-TA administration the nodules appear hypointense and are surrounded by a hyperintense peripheral rim. Partial wash-out is apparent on the portal venous phase image (c). In the hepatobiliary phase (d) 1 h after contrast agent administration, the lesion located in segment IV of the liver appears slightly hypointense, due to non-specific intra-lesional pooling of the contrast agent in the necrotic components of the lesion. The lesion in segment II appears homogeneously hypointense

Liver Dynamic Enhancement Mri

Fig. 30a-f. Metastases from malignant melanoma after SH U 555 A. The pre-contrast TSE T2-weighted image (a) reveals a small, round hyperintense nodule (arrow) in segment VI of the liver. On the corresponding pre-contrast GRE T1-weighted image (b), the lesion is hy-pointense. During the dynamic study after injection of SH U 555 A (c-e), the nodule shows weak and progressive enhancement, mainly in the equilibrium phase (e), and a thin peripheral hyperintense rim is easily visible. In the reticuloendothelial phase (f) the lesion appears hyperintense, due to the lack of uptake of SH U 555 A since there are no functioning Kupffer cells in the lesion

Fig. 30a-f. Metastases from malignant melanoma after SH U 555 A. The pre-contrast TSE T2-weighted image (a) reveals a small, round hyperintense nodule (arrow) in segment VI of the liver. On the corresponding pre-contrast GRE T1-weighted image (b), the lesion is hy-pointense. During the dynamic study after injection of SH U 555 A (c-e), the nodule shows weak and progressive enhancement, mainly in the equilibrium phase (e), and a thin peripheral hyperintense rim is easily visible. In the reticuloendothelial phase (f) the lesion appears hyperintense, due to the lack of uptake of SH U 555 A since there are no functioning Kupffer cells in the lesion phase images metastases can show a fleeting ring enhancement that blurs the margins of the lesion. This corresponds to desmoplastic reaction, inflammatory infiltration and vascular proliferation in the tumor-liver parenchymal margin. The enhancement progresses centrally with concomitant peripheral wash-out. In the equilibrium phase around 10 min after administration of contrast agent, some lesions may show a peripheral hypointense rim ("peripheral wash-out" sign).

Dynamic phase imaging after Gd-BOPTA administration reveals identical enhancement patterns to those seen with conventional extracellular Gd-based contrast agents. Since the lesions are unable to take up Gd-BOPTA they appear as homogeneously hypointense on delayed T1-weighted images [2]. For metastases showing desmoplastic reaction, an accumulation of Gd-BOPTA in the fi-brotic part may be observed, which can remain for several hours. In these cases, the observation of a peripheral hypointense halo is highly suggestive of the malignant nature of the lesion (Fig. 31).

The enhancement pattern after mangafodipir trisodium is similar to that after Gd-BOPTA; an increase of the liver-to-lesion contrast-to-noise ratio occurs because of the lack of Mn++ uptake (Fig. 32).

Since metastases do not contain Kupffer cells, the contrast-to-noise ratio and hence lesion detection and conspicuity is improved after SPIO injection when compared to unenhanced T2-weighted images (Fig. 33) [28].

Due to the non-specific behavior of malignant liver lesions after SPIO injection, some authors have proposed a dual contrast study in order to improve lesion characterization. With this approach, pre- and post-SPIO images are obtained, followed, after bolus injection of a conventional Gd agent, by multiphasic dynamic T1-weighted GRE images. Contrast agents such as Gd-BOPTA and Gd-EOB-DTPA, which inherently have both dynamic extracellular characteristics and delayed hepatospecific characteristics, have clear advantages over such an approach.

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Responses

  • Keiren
    How to prevent hypovascular?
    3 years ago
  • abbie
    Why would you have hypovascular in liver?
    2 months ago

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