Surgical Resection

The role of surgical resection in the treatment of hepatic metastases of primary colorectal carcinomas is well-recognized and may contribute to the five year survival of 25% to 37% of affected patients [9]. However, the approach to the surgical treatment of hepatic metastases from primary tumors other than colorectal cancer is less obvious, and is highly dependent upon the type of primary tumor. Nevertheless, a reported five year survival rate of 21% after resection of metastases from non-colorectal carcinomas can be considered comparable to that for metastases from colorectal carcinomas [ 12].While outstanding results are obtained when metastases from neuroendocrine tumors are resected, less favorable results are frequently obtained from the resection of metastases from gastric or breast cancer.

As only about 30% of the patient population with hepatic metastatic disease is eligible for liver resection, preoperative magnetic resonance imaging (MRI) provides detailed information for surgical therapy planning, as it can help determine the number and location of intrahepatic lesions [32]. Exact anatomic description of the tumor spread in correlation with the segmental distribution and the course of major hepatic vascular structures is es-

Fig. 1a-f. Pre- and post-surgical imaging in a patient with liver metastases from colorectal cancer and postoperative bilioma formation. The preoperative imaging studies show a metastasis with high SI on the T2-weighted image (a, arrow) and typical peripheral wash-out on the contrast-enhanced T1-weighted fat-suppressed image post-injection of Gd-BOPTA (b). On post-surgical imaging, three weeks after resection of the liver metastases (c-f), a triangular defect from atypical resection of the lesion is visible on axial (c) and coronal (d) T2-weight-ed HASTE images (arrows). The resulting defect is filled with a high SI fluid, which aspiration showed to be a bilioma formation. Note susceptibility artifacts from surgical clips on the unenhanced T1-weighted image (e, arrows). In the equilibrium phase post-contrast agent injection (0.05 mmol/kg BW Gd-BOPTA) no enhancing rim surrounding the defect is visible, which excludes an inflammatory process or abscess formation

Fig. 1a-f. Pre- and post-surgical imaging in a patient with liver metastases from colorectal cancer and postoperative bilioma formation. The preoperative imaging studies show a metastasis with high SI on the T2-weighted image (a, arrow) and typical peripheral wash-out on the contrast-enhanced T1-weighted fat-suppressed image post-injection of Gd-BOPTA (b). On post-surgical imaging, three weeks after resection of the liver metastases (c-f), a triangular defect from atypical resection of the lesion is visible on axial (c) and coronal (d) T2-weight-ed HASTE images (arrows). The resulting defect is filled with a high SI fluid, which aspiration showed to be a bilioma formation. Note susceptibility artifacts from surgical clips on the unenhanced T1-weighted image (e, arrows). In the equilibrium phase post-contrast agent injection (0.05 mmol/kg BW Gd-BOPTA) no enhancing rim surrounding the defect is visible, which excludes an inflammatory process or abscess formation sential. Infiltration of central hilar vascular structures such as the portal vein, hepatic artery and central hepatic bile ducts almost always excludes a possible treatment by liver resection. Moreover, ex-trahepatic tumor growth and infiltration into adjacent organs should be carefully evaluated.

Post-operative MRI of the liver within the first four weeks is helpful for the detection of surgical complications such as hematoma or abscess formation, perfusion disturbances or bilioma formation. Bilioma or abscess formations are characterized by a hypo- to hyperintense signal on T1-weighted images and by typically high signal intensity on T2-weighted images. A lack of central enhancement is seen both with bilioma and abscess formations, however if a pronounced peripheral enhancement, indicating an abscess wall, can be identified, the patient may require intervention-al drainage or surgical revision (Fig. 1). As regards bilioma formations, follow-up studies are advised since some bilioma formations resolve spontaneously with time. In the case of port-surgical biliary leaks, the precise location of the leak can frequently be accertained with the use of MR contrast agents such as Gd-BOPTA that are excreted in part through the hepatobiliary system. In this regard, T1-weighted images acquired during the hepatobiliary phase at around 2h after injection will usually reveal the location of the leak through contrast extravasation at the site of bile duct damage.

In most cases, surgical resection involves the removal of two or more liver segments and post-surgical follow-up imaging does not differ greatly from pre-surgical imaging. However, if the borders of the resected liver lesions are within 2 cm of the resection margin, special attention should be paid to the neighboring areas at follow-up. Using T1-weighted imaging, detailed evaluation of the j

Fig. 2a-c. Recurrent tumor after atypical liver resection. On the unenhanced T2-weighted TSE image (a), an area of slightly increased SI surrounds the resection defect (arrows). On the Tl-weighted arterial phase image (b) after bolus injection of contrast agent (0.05 mmol/kg BW Gd-BOPTA), an irregular shaped margin of increased enhancement is visible (arrows), which is separated by a tissue rim from the resection defect. This rim of tissue represents recurrent tumor which on the hepatobiliary phase Tl-weighted image (c) 1 hour after contrast agent administration, shows no uptake of contrast agent. This indicates a recurrent tumor rather than just a post-surgery perfusion abnormality

Fig. 2a-c. Recurrent tumor after atypical liver resection. On the unenhanced T2-weighted TSE image (a), an area of slightly increased SI surrounds the resection defect (arrows). On the Tl-weighted arterial phase image (b) after bolus injection of contrast agent (0.05 mmol/kg BW Gd-BOPTA), an irregular shaped margin of increased enhancement is visible (arrows), which is separated by a tissue rim from the resection defect. This rim of tissue represents recurrent tumor which on the hepatobiliary phase Tl-weighted image (c) 1 hour after contrast agent administration, shows no uptake of contrast agent. This indicates a recurrent tumor rather than just a post-surgery perfusion abnormality resection margins is sometimes difficult due to susceptibility artifacts caused by surgical clips (Fig. 1e). Follow-up evaluations may also be difficult in cases of atypical resection. Likewise, when liver lesions are enucleated with a margin of 2-3 cm a clear identification of the resection margins may not always be possible. Additionally, signal intensity on unenhanced T1-weighted and T2-weighted images as well as on T1-weighted dynamic imaging may be influenced by hemorrhage, seroma formation, inflammation and ischemia of surrounding liver tissue, particularly during the first one to two months after resection. Thus follow-up imaging is usually best performed at three or more months after resection, in order to minimize the influence of post-surgical changes. In such cases, hyperintense nodular regions on T2-weighted images, hypointense areas on unen-hanced Ti-weighted images and irregular vascularization on T1-weighted dynamic images is usually indicative of a recurrent tumor (Fig. 2). Since the majority of patients develop recurrent metastases after surgical resection, careful restaging is mandatory.

Furthermore, in post-surgical follow-up imaging, special care should be taken to detect intra-hepatic or intraperitoneal seeding of tumor cells from surgery. This is particularly important in instances of atypical resection of liver metastases.

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