A diffuser for a centrifugal impeller assembly of a gas turbine engine includes a diffuser case having a plurality of vanes extending therein defining a plurality of circumferentially distributed angled passages in communication with an inlet space. Each vane includes a bleed port defined in a suction surface thereof, in proximity of the leading edge. The diffuser case includes a passive fluid communication defined at least partially through each one of the vanes between each bleed port and the inlet space upstream of the leading edge, such that air bled through the bleed ports is recirculated upstream of the leading edges to the inlet space to increase a surge margin of the diffuser.