Contrast clearance analysis in post-operative brain metastases resection cavities: case series and literature review.

Background: The aims of this study were to assess how previously described treatment response assessment maps/contrast clearance analysis (TRAMs/CCA) imaging appearances may present in post-operative brain metastasis resection cavities and to discuss their potential contribution to clinical decision-making. Methods: This retrospective descriptive case series included four patients with surgically resected brain metastases. Cases were purposively selected to illustrate distinct post-operative TRAMs/CCA imaging appearances resembling those previously described after stereotactic radiosurgery (SRS). All included patients had histologically confirmed metastatic disease and underwent routine post-operative magnetic resonance imaging (MRI) surveillance. TRAMs/CCA imaging was performed using a 1.5-T MRI scanner according to the Brainlab Elements protocol for CCA with standard-dose gadolinium administration. Early and delayed post-contrast 3D T1-weighted sequences were analyzed to generate contrast clearance maps, providing complementary imaging information regarding contrast enhancement characteristics of post-operative lesions. Post-operative cavities were assessed in multidisciplinary consensus. Results: Four representative CCA/TRAMs imaging appearances within post-operative resection cavities, showing features analogous to TRAMs/CCA imaging features previously described after SRS, were observed and correlated with conventional contrast-enhanced T1-weighted MRI findings and follow-up outcomes. Appearances characterized by the absence of early contrast clearance or by extensive persistent delayed retention despite marked contrast enhancement were observed in cases with post-operative changes without local recurrence; in these cases, adjuvant SRS was deferred and MRI surveillance was performed. Mixed TRAMs/CCA appearances with focal areas of early contrast clearance were observed in a case that subsequently developed local recurrence within regions considered suspicious on TRAMs/CCA. In contrast, appearance characterized by a thin peripheral early contrast clearance with adjacent delayed contrast retention was observed in a case with intermediate post-operative findings for which follow-up imaging was not available. Conclusions: TRAMs/CCA may represent a useful non-invasive adjunct to conventional MRI for SRS planning after brain metastases resection. These findings support further investigation of TRAMs/CCA as a potential adjunct for treatment planning and longitudinal surveillance. Further prospective studies are warranted.