MMP9 and arteriovenous malformations of the brain: However, when compared to control samples (median; range, 97.3; 65.4 pg/ml), MMP-9 expression was significantly higher in BAVM patients preoperatively (median; range, 4,551.0; 12,585.7 pg/ml) (p = 0.002; Mann–Whitney U-test) and postoperatively (median; range, 5,589.5; 12,939.7 pg/ml) (p = 0.002; Mann–Whitney U-test) (Fig. 1F).