The target sign in colorectal liver metastases: an atypical Gd-EOB-DTPA “uptake” on the hepatobiliary phase of MR imaging

To describe the MRI findings in colorectal cancer liver metastases using gadoxetic acid (Gd-EOB-DTPA), with special emphasis on the target feature seen on the hepatobiliary phase. The medical records of 45 colorectal cancer patients with an overall number of 150 liver metastases were reviewed. All patients underwent Gd-EOB-DTPA-enhanced MRI before any kind of treatment. We retrospectively evaluated, for each lesion, the signal intensity on the T1-weighted, T2-weighted, and diffusion-weighted images. Additionally, the enhancement pattern during the arterial-, portal-, equilibrium-, and hepatobiliary-phase was assessed. Fourteen lesions had a pathological correlation. Lesions size was 5–40 mm (mean 15 mm). All metastases were hypointense on T1-w imaging. Ninety-nine lesions (66%) had a central area of very high signal intensity on T2-w imaging. Fifty-one metastases (34%) were hyperintense on the T2-w images. In DWI, all lesions had a restricted diffusion. The mean ADC value was 1.31 × 10−3 mm2/s (range 1.10–1.45 × 10−3 mm2/s). During the arterial-phase imaging, 61 lesions (41%) showed a rim enhancement, while 89 lesions (59%) appeared as hypointense. All lesions had low signal intensity in the portal and equilibrium phase. Thirty-nine percent of the lesions also showed an enhancing rim on the portal-phase images. During the hepatobiliary phase, 80 lesions (53.3%) were hypointense, while 70 lesions (46.7%) had a target appearance. A number of metastases show an atypical contrast medium uptake during the hepatobiliary phase of gadoxetic acid-enhanced MRI, consisting in a target appearance.