MR Imaging Correlates of Intratumoral Tissue Types within Colorectal Liver Metastases: A High-Spatial-Resolution Fresh ex Vivo Radiologic-Pathologic Correlation Study

Purpose: To analyze the direct relationship between complex internal magnetic resonance (MR) signal intensity (SI) patterns observed in colorectal liver metastases and their microscopic tissue characteristics. Materials and Methods: The institutional ethics board approved this study. In seven consecutive patients undergoing hepatic resection for liver metastases (primary colorectal in six, breast mistaken for colorectal in one), the resected fresh ex vivo liver specimen was examined with T1-weighted (repetition time msec/echo time msec, 9/4.4-4.8) and T2-weighted (2500/90) MR imaging by using a voxel size of 0.47 x 0.7 x 2 mm. The liver was sectioned in a concordant plane, and individual histologic slides were scanned and reconstructed to form a whole-mount pathologic image of the metastases. A pathologist identified the regions of interest for intraacinar necrosis (IAN), loose or dense fibrosis, and moderately and poorly differentiated cells within the metastases, and these regions were matched to the corresponding MR image. The morphologic and SI patterns were noted. The normalized ratio between the SI of these regions and that of the background liver was determined on T1- and T2-weighted images. Pairwise differences between tissue types were calculated by using linear mixed model, with the P values adjusted for multiple comparisons by using the method of Sidak. Results: A total of 98 zones were defined after pathologic analysis. On T2-weighted images, IAN was significantly lower in SI (P < .05) than the other tissues types. On T1-weighted images, IAN was significantly higher in SI than the other tissues types (P < .001). The type of necrosis encountered in these specimens was exclusively IAN. Qualitatively IAN had a specific pattern of SI (hypointense on T2-weighted and hyperintense on T1-weighted images). Other tissues types, including fibrosis, showed a pattern of hyperintensity on T2-weighted and hypointensity on T1- weighted images. Conclusion: IAN seen in colorectal metastases exhibits high T1- weighted SI and mixed T2-weighted SI. This SI pattern is unusual for common benign liver lesions and may be helpful in the MR imaging diagnosis of colorectal liver metastases. (C) RSNA, 2010.