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

Purpose: 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. Material and methods: 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. Results: 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. Conclusion: A number of metastases show an atypical contrast medium uptake during the hepatobiliary phase of gadoxetic acid-enhanced MRI, consisting in a target appearance.