Necrosis or Hematoma After Juvederm Lip Injections?

How do you know if you have recieved a hematoma vs necrosis immediately after a juvederm plus injection in the lip. There was very little Juve injected (aprox 0.2 ml) in center of one side top lip and immediate purple and black filled sack formed underneath injection site, very swollen and dark in color. The pain subsided within a couple hours. Anti-inflamatories and ice were applied immediately, but after couple hours we changed to nitropaste and warm compress due to the darkness of the swollen sack on underside of top lip just below injection site.