The hymen usually has remnants in an adult woman in a ring around the entrance to the vagina. It often looks like irregular bits of tissue - but you can usually pretty clearly see a whole ring of tissue around the opening. It is a landmark used when doing a vaginal repair, too. I have only occasionally seen bad swelling like you describe - usually in folks who pushed a long time and often in women who had epidurals and lots of IV fluids, but occasionally it happen spontaneously. I don't think it usually re-occurs. Sometimes I'll see fragments of the hymenal ring that swell amazingly, but they usually get better in a few days. Sitz baths, and resting a little in knee-chest several times a day seem to help.