Change in postsurgical cavity size within the first 30 days correlates with extent of surrounding edema: Consequences for postoperative radiosurgery

OBJECTIVE: Resection cavity diameter of less than 40 mm is required to be eligible for stereotactic radiosurgery (SRS), after gross total resection of brain metastasis at our institution. Our study evaluates the correlation between vasogenic edema and change in cavity size for 30 days. METHODS: Cavity size was measured on the postoperative and follow-up magnetic resonance imaging. Vasogenic edema was quantified as the largest axial measurement of T2 hyperintensity surrounding the resection cavity (postoperative magnetic resonance imaging). RESULTS: Thirty-nine resection cavities (37 patients) were reviewed. There was a statistically significant (Pearson coefficient =-0.35; P = 0.02) negative correlation between edema and change in cavity size. An arbitrary cutoff value of a 15-mm edema yielded a sensitivity of 96% and a specificity of 65% (P < 0.001) to predict 10% decrease in cavity size. CONCLUSIONS: In patients with cavity size close to the size cutoff for SRS, rescanning closer to the date of SRS should be considered, especially if there is significant edema surrounding the cavity.