Imperforate hymen is also known as nonporous hymen. The incidence of imperforate hymen is about 0.015 %. Imperforate hymen mainly obstructs the discharge of vaginal secretions. It may be asymptomatic at childhood due to minimal vaginal secretions, but at puberty, as both the vaginal and cervical secretions gradually increase, they accumulate in the vagina and lead to a sense of heaviness in the lower abdomen. After menarche, as the menstrual blood cannot drain out, it accumulates in the vagina forming a vaginal hematoma after several menstruations. Subsequently, it may lead to uterine and tubal hematomas, and eventually retrograde flow will enter into the pelvic cavity forming pelvic hematomas. Clinical symptoms are obvious with a cyclical lower abdominal pain, which progressively increases in intensity.

On gynecological examination, a bulging hymen can be seen, with a purple blue surface; on rectal examination, a vaginal mass bulging into the rectum is felt as a palpable pelvic mass. With a finger pressing on the vaginal mass, the bulging hymen can be made more obvious. Ultrasound scan may show accumulated fluid in the vagina and even in the uterine cavity.

It is a rare anomaly. There is a film covering the vaginal opening with just a pin hole opening as first described by Capraro in 1968 [1]. Since the pin hole is often difficult to detect, it is often misdiagnosed as an imperforate hymen. According to the sizes of the pin hole, the presenting symptoms will be different. Some patients have periodic menstruations with moderate amount of menstrual blood outflow, but a lot of blood still accumulates in the vagina; sometimes the periods are irregular; some patients presented with delayed menarche, with their chief complaints that include periodic abdominal pain and painful pelvic mass due to hematoma formation [2]. Microperforate or imperforate hymen can occur as an isolated anomaly, but it can also be associated with other reproductive tract anomalies, such as bicornuate uterus, vestibular anomalies, and anal atresia [3].

Similar to imperforate hymen, microperforate hymen can cause reflux of vaginal secretions and blood into the peritoneal cavity forming a pelvic mass. Unlike imperforate hymen, it will also cause recurrent urinary tract infections and sometimes a pelvic abscess. It is because the pinhole opening can have communication to the outside, through which bacteria will enter and multiply in the accumulated effusion or blood in the vagina or the pelvis leading a pelvic abscess. Bacteria can also migrate out of the vaginal opening, enter into the urethra, and cause recurrent urinary tract infections. On the contrary, patients with imperforate hymen do not have these presentations because their vaginas do not communicate with the outside [4]. The microperforate hymen is mainly diagnosed by examination under general anesthesia, and nowadays, fiber-optic hysteroscopy can be useful in its diagnosis together with simultaneous examination of any anomalies in the vagina and cervix [5].

A metal urinary catheter should be used if possible to guide its position to avoid bladder injury. The surgeon should wear double gloves and insert the index finger of the left hand into the anus pressing towards the vagina for guidance, so as to avoid injury to the rectum. The incision should be at the most prominent part of the bulging hymen, though it will depend on the personal choice. The incision can be a “cross” incision, a vertical incision or a puncture incision at the center. Some surgeons think that it should begin with a small incision (especially for a thickened hymen), so as to reduce the rate of blood flow and hence to prevent vasovagal reaction due to the sudden decompression of the vaginal hematoma. Then, the outer glove of the left hand is removed to examine if the vaginal opening can accommodate one finger. Attention should be paid to avoid damaging the urethra and rectum during surgery. Finally, the vagina and cervix should be examined for other associated anomalies.

After opening the imperforate hymen, the retained menstrual blood will drain off. Any blood should be mopped up with gauze, and the cervix can now be visualized and examined. In the presence of a cervical adhesion or stenosis, a small uterine dilator is used to discharge any intrauterine blood retention. Tubal blood collection will gradually drain out following the operation. The abdomen should not be pressed or kneaded to avoid rupture of a hematoma or to force more retained blood flowing into the peritoneal cavity.

Any redundant hymen tissue should be cut off from the incision wounds. Absorbable sutures are used to suture the edges, while a very thin hymen wound without bleeding may not require suturing. In the literatures, absorbable sutures No. 3 “0” or No. 4 “0” are recommended to suture the wound edges or to cauterize wound edges with diathermy, so as to avoid wound adhesion with subsequent stenosis.