Hepatic colorectal metastases: correlation of MR imaging and pathologic appearance

Results of magnetic resonance (MR) imaging examinations for 76 patients with proved colorectal metastases to the liver were retrospectively reviewed. Signal intensity and morphologic patterns of 157 lesions were scored. The morphologic patterns were correlated with the histologic material obtained at segmental hepatic resections or excisional biopsies in 33 patients. In 154 lesions (98%) colorectal metastases to the liver were found to be hyperintense on MR images acquired with a long repetition time/echo time; in 77 lesions (49%) central low-signal-intensity changes were seen. Virtually all larger lesions demonstrated areas of low signal intensity within the tumor. These areas were found to reflect histologic findings of coagulative necrosis and desmoplasia within the tumor. Peripheral hyperintense halos around central hypointense areas encompassed the growing tumor margin and variable degrees of cell necrosis. Hypointense peripheral rims, which correspond to abnormalities of surrounding hepatic parenchyma, were seen in 40 lesions (25%). This sign should not be assumed to represent the fibrous pseudocapsule of primary hepatic malignancy. No correlation between tumor grade (differentiation) and tumor morphology was observed.