Teste if MemoryStream was created

Hi All !
   How can we test if a memory stream was created ?

Var
   mStream : TMemoryStream;
Begin
   mStream := TMemoryStream.Create;
   mStream.Position := 0;
   mStream.Free;
   if mStream exists Then     ----->> How to do it ?
      ShowMessage('Mstream exists')
   Else
      ShowMessage('Mstream doesn´t exists');
End;

Thanks a lot.

Gustavo