Background: Diffusion-weighted MRI (DWI) has been used in neurosurgical practice mainly to distinguish cerebral\nmetastases from abscess and glioma. There is evidence from other solid organ cancers and metastases that DWI\nmay be used as a biomarker of prognosis and treatment response. We therefore investigated DWI characteristics of\ncerebral metastases and their peritumoral region recorded pre-operatively and related these to patient outcomes.\nMethods: Retrospective analysis of 76 cases operated upon at a single institution with DWI performed pre-operatively\nat 1.5T. Maps of apparent diffusion coefficient (ADC) were generated using standard protocols. Readings were taken\nfrom the tumor, peritumoral region and across the brain-tumor interface. Patient outcomes were overall survival and\ntime to local recurrence.\nResults: A minimum ADC greater than 919.4 Ã?â?? 10-6 mm2/s within a metastasis predicted longer overall survival\nregardless of adjuvant therapies. This was not simply due to differences between the types of primary cancer\nbecause the effect was observed even in a subgroup of 36 patients with the same primary, non-small cell\nlung cancer. The change in diffusion across the tumor border and into peritumoral brain was measured by the\nââ?¬Å?ADC transition coefficientââ?¬Â or ATC and this was more strongly predictive than ADC readings alone. Metastases with a\nsharp change in diffusion across their border (ATC >0.279) showed shorter overall survival compared to those\nwith a more diffuse edge. The ATC was the only imaging measurement which independently predicted overall survival\nin multivariate analysis (hazard ratio 0.54, 95% CI 0.3 ââ?¬â?? 0.97, p = 0.04).\nConclusions: DWI demonstrates changes in the tumor, across the tumor edge and in the peritumoral region which\nmay not be visible on conventional MRI and this may be useful in predicting patient outcomes for operated cerebral\nmetastases.
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