Microvascular surgery: Surgery on very small blood vessels such as those only 3 to 5 millimeters in diameter. Microvascular surgery is done through an operating-room microscope using specialized instruments and tiny needles with ultrafine sutures. Microvascular surgery is used to reattach severed fingers, hands, arms, and another amputated parts to the body by reconnecting the small blood vessels and restoring the circulation before the tissue starts to die. Microvascular surgery also can be used in reconstructive surgery. See also: Replantation.