Diffusion-weighted MRI of metastatic liver lesions: is there a difference between hypervascular and hypovascular metastases?

ABSTRACT

BACKGROUND: Different perfusion characteristics and histopathologic features of liver metastasis may potentially lead to different diffusion-weighted magnetic resonance imaging (DW-MRI) characteristics which can affect the performance of DW-MRI in their diagnosis. PURPOSE: To compare ADC values of hypervascular and hypovascular metastases and the added value of DW-MRI to T2-weighted (T2-w) images in their detection. MATERIAL AND METHODS: In this retrospective study, 46 patients (21 with hypervascular, 25 with hypovascular liver metastases) who had undergone abdominal MRI were included. Two independent observers first reviewed T2-w images only and then T2-w+DW-MR images and recorded number of metastases in each session. Lesion detection rate was compared using McNemar test. ADC of metastases in each patient was measured and compared between hypo- and hypervascular lesions using t-test. RESULTS: A total of 153 hypervascular and 187 hypovascular metastases were detected at consensus review. Two observers detected significantly more hypervascular metastases on T2-w+DW-MR image review session compared to T2-w image only review session (reader 1 148 [96.7%] vs. 129 [84.3%], P=0.002; reader 2 125 [81.9%] vs. 113 [73.8%], P=0.004). Detection rate of hypovascular metastases was similar between two sessions for both observers (reader 1 180 [96.2%] vs. 184 [98.4%]; reader 2 176 [94.1%] vs. 180 [96.2%], P>0.05). The mean ADC value of hypervascular metastases was significantly lower than mean ADC value of hypovascular metastases (1.23+/-0.31 × 10(-3)mm(2)/s vs. 1.49+/-0.19 × 10(-3)mm(2)/s) (P=0.001). CONCLUSION: Liver metastases are not a homogenous group of lesions with uniform DW-MRI features. Hypervascular metastases demonstrate significantly lower ADC values compared to hypovascular metastases. DW-MRI improved detection of hypervascular metastases compared to T2-w images alone and is a useful adjunct to T2-w images for their detection.