This occurs in consequence of the retention and accumulation of material in the utems. It results, therefore, from Obstruction of the vagina or of one of the orifices of the uterus. There may be imperforate hymen or congenital closure of the external or internal os (generally the external). When the period of the puberty is reached and menstruation begins, the blood accumulates in the uterus and there may be enormous distension, the contents having a tarry or pulpy character. This condition is designated Hsematometra. The uterus may assume the size of the pregnant organ, and there is thickening of its walls, which, however, are loose. If escape is not provided artificially the uterus may actually rupture; not usually into the peritoneum, but, after the formation of adhesions, into some neighbouring organ. The rupture is by a process of ulceration from within, unless external violence bursts the distended organ.

There may be an acquired Obstruction of the os uteri as from chronic catarrh, or even from inflammation occurring after delivery. In such cases also we may have a hsematometra from accumulation of menstrual blood. It is more common, however, to have such closure after menstruation has permanently ceased, and in that case a catarrhal secretion may accumulate and distend the uterus. After a time the contents, which are at first mucous in character, become serous, and the condition called Hydrometra is brought about.

Lastly, the organ is sometimes distended with Gas, a condition designated Physometra. This may be the result of decomposition of the accumulated fluid in hydrometra, or from decomposition of retained clots, etc.; but cases have occurred in which the cavity has been dilated with gas and assumed considerable proportions without apparent cause.