Some young girls suffer from an imperforated hymen. This is a physical condition in which the hymen (the small membrane at the entry to the vagina) completely obstructs the vaginal opening. Consequently, menstrual blood cannot flow out and instead it accumulates inside the vagina. This problem is rare (one in 2000 young girls).
How is it repaired?
Surgery under anaesthesia involves an incision into the hymen to open a passage, or even to remove it if it's very thick. The surgeon puts a pipe in place to drain out the accumulated blood. This procedure is medically referred to as a hymenectomy.
Consequences
Periods begin and sexual relationships are possible. Stomach pains usually disappear, along with urinary problems as well (the build-up of blood can press against the bladder).