[Value of diffusion-weighted imaging for diagnosing vertebral metastases due to prostate cancer in comparison to other primary tumors].

PURPOSE

Several publications have reported that the apparent diffusion coefficient is generally lower in metastatically affected vertebrae. Therefore, metastases are represented in diffusion-weighted images by increased signal intensity in comparison to unaffected vertebrae. However, there were indications that metastases due to prostate cancer may differ from this. Therefore, the contrast behavior of vertebral metastases due to prostate cancer or tumors with another histology are to be systematically studied using diffusion-weighted images. The present study is intended to examine whether the two groups differed and whether possible differences depended on the degree of sclerosis.

MATERIALS AND METHOD

In a retrospective study the vertebral metastases of patients with prostate cancer (n = 18) were compared to those of patients with tumors of another histology (n = 20). A steady-state free precession sequence was used for the diffusion-weighted imaging. Additionally, a T1 weighted sequence before and after administration of contrast agent as well as a fat suppressed T2 weighted sequence were performed. The contrast behavior of the metastases was evaluated for all four sequences and was compared to that of the unaffected parts of the vertebra.

RESULTS

In 18 patients of the tumor group, the vertebral metastases showed positive contrast in the diffusion-weighted images, and 2 had minimally negative contrast up to - 0.04. In the prostate cancer group, the contrast was positive in 9 patients and negative in 9. 6 of the metastases with negative contrast had an osteoblastic metastasization, 1 had an osteolysis, and 1 had a normal finding in the conventional X-ray image. Between the tumor group and the prostate cancer group, the medians of the contrasts were not significantly different (p = 0.054).

CONCLUSION

In general, the metastatically affected vertebrae appear hyperintense in the diffusion-weighted images. This observation is only true for some vertebral metastases due to prostate cancer. The cause for this seems to be the degree of sclerosis of the metastases. Thus, it cannot be generally deduced from the hypointensity in diffusion-weighted images that a lesion is benign.