The hymen forms at the junction of the upgrowth of endoderm from the urogenital sinus and the downgrowth of the fused paramesonephric duct. Normally, it is a thin incomplete membrane surrounding the vaginal orifice with one or more apertures that allow escape of menstrual blood. It is usually torn during the first coitus.
Sometimes in development, canalisation of the upgrowth of the urogenital sinus fails and the hymen is imperforate. It may be detected as a mucocolpos - accumulation of mucous in the vagina behind the hymen - but frequently, is missed.
Undetected, the condition usually remains asymptomatic until puberty. The post-pubertal patient may complain of amenorrhoea as the outflow of menstrual blood is obstructed. Blood accumulates behind the imperforate hymen and is inspissated. With successive periods, the collection increases. The child is menstruating but it is concealed - cryptomenorrhoea.
Gradually, the vagina becomes distended with blood - haematocolpos - which in severe cases, may extend up into the uterus - haematometra - or fallopian tubes - haematosalpinx.
Examination shows a mass rising from the pelvis into the abdomen. A mucocolpos has a white appearance whereas in a haematocolpos, the vulva is tinted blue by the underlying altered blood. The distended vagina may be detected on rectal examination.
Treatment is by incising the hymen which ideally, should occur in the newborn period or at the time of the menarche when the tissues are oestrogenised.
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