Differentiation of hepatic metastases from hepatic hemangiomas and cysts by using MR imaging.

T1-weighted and T2-weighted pulse sequences were employed for MR imaging of hepatic metastatic tumors (98 patients), hemangiomas (24 patients), and cysts (seven patients); a 0.6-T superconducting magnet was used. In a retrospective study, signal intensity and morphology were used to establish criteria for differentiating metastases from hemangiomas and cysts. The signal intensity of the lesion alone failed to be an etiologic discriminator because over 96% of all masses had a signal intensity less than that of liver on T1-weighted sequences, and at least 90% had a signal intensity greater than that of liver on T2-weighted sequences. Morphologic features depicted on T2-weighted images were more specific than those depicted on T1-weighted images in differential diagnosis. Amorphous, target, and halo signs and a change in morphology were present only in metastatic disease, with a frequency of 45%, 27%, 13%, and 12%, respectively. Two other morphologic patterns--doughnut and lightbulb signs--were found to have overlapping causes. Overall, at least one of the specific signs was observed in 92% of patients with metastatic disease. These data suggest that T2-weighted pulse sequences are essential for discriminating between hepatic metastases and hepatic hemangiomas and cysts. MR imaging is a promising technique for distinguishing these lesions.