Background: The phenomenon of "contrast media leakage" in metastatic brain tumors, where contrast enhancement of perilesional edema can overestimate actual tumor volume.

Methods: The radiologic and pathologic characteristics of 3 surgically resected metastatic brain tumors with contrast media leakage were analyzed. Five metastatic tumors were treated with gamma knife radiosurgery (GKRS), deliberately avoiding areas of contrast media leakage. Methods: The characteristics of these tumors, the administered radiation dosage, and progression-free survival were evaluated.

Results: The region of "contrast media leakage within edema" showed different signals from tumor boundaries on T2-weighted magnetic resonance imaging, fluid-attenuated inversion recovery, and apparent diffusion coefficient maps. No increased cerebral blood volume and a low transfer coefficient were indicated on perfusion images. Pathologically, these areas showed prominent endothelial proliferation and perivascular lymphocyte infiltration without tumor cell infiltration. Immunohistochemical staining revealed a weak positive for clauidin-5 and a strong positive with antibodies against leukocyte common antigen and cluster of differentiation 68. Five lesions treated with GKRS were adenocarcinomas of lung origin. The median radiation volume was 3.10 cc (range, 2.32-3.78), and the median radiation dose was 22 Gy (range, 20-22). Treatment responses were nearly complete in 1, partial in 3, and stable in 1. There were recurrences at 6.0 and 10.0 months after GKRS. Median progression-free survival was 18.2 months (95% confidence interval: 9.2-27.1), and there was no treatment-related complication.

Conclusions: This study revealed that the region of "contrast media leakage within edema" showed more pronounced blood-brain barrier disruption associated with inflammatory cells. It was effective when the GKRS targeted the actual tumor, excluding the area with contrast media leakage.