Infarction refers to tissue death which is what necrosis actually is. An infarction is due to a blockage of the blood supplying a tissue in the body. When this occurs, the tissue will die due to a lack of oxygen which the blood would have been unable to supply due to the blockage. The supplying artery can be blocked due to a build-up of plaque, a clot, a tumor, or constricted due to drug use. Necrosis is technically the premature death of cells in living tissue. Trauma, infection, arterial blockage can all lead to tissue death. Necrotic tissue sends different signals as compared to cells undergoing natural tissue death. This causes the immune system to not engulf the dead cells, which causes a buildup near the site of dead cells and debris. Surgery will sometimes be necessary to remove this tissue. Other reasons tissue may become necrotic are cancer, poisons, injury.