Diffusion-Weighted Imaging of Brain Metastasis: Correlation of MRI Parameters with Histologic Type

To compare the diffusion properties of brain metastases as imaging biomarkers in various types of tumours, to determine their histology and origin.

Magnetic Resonance Imaging (MRI) and diffusion-weighted imaging (DWI) were used to retrospectively study the data of 143 patients suffering from brain metastases. Four categories of primary tumours with metastases to the brain were included: lung carcinoma (n=102, 71.3%); breast carcinoma (n=27, 18.8%); colon carcinoma (n=8, 5.6%); and others (n=6, 4.2%). The Apparent Diffusion Coefficient (ADCmin ) values, as well as the normalised ADC ratio (nADC), were determined. The lesions on the DWI were categorised as follows: type 1, with negative findings on DWI; type 2, which were isointense with the normal cortical grey matter; type 3, which were hyperintense compared to the normal cortical grey matter.

The diffusion type, mean ADCmin, and mean nADC showed statistically significant differences in different types of metastases. In the subgroup analysis, it was found that type 3 was the diffusion type found most extensively in the brain metastases of small cell carcinoma (SCLC) (n=52, 65.8%, p < 0.000). Furthermore, the mean ADCmin and nADC values were the least for the brain metastases of the SCLC (552.0 ± 134.2 and nADC = 0.8 ± 0.1, p < 0.000, respectively). The value of the mean ADCmin was low in the human epidermal growth factor receptor 2 (HER-2) negative groups than in the HER-2 positive groups at 786.8 ± 299.1 vs 844.8 ± 141.3 (p < 0.006).

Our findings indicated that there is a correlation between diffusion parameters as imaging biomarkers of the solid component of brain metastases of primary tumours and the tumour histology.