Endometrium of cavitary rudimentary horns in unicornuate uteri

The rudimentary horns removed from ten patients with unicornuate uterus, subclass A1b, were studied by light and scanning electron microscopy. Seven of the horns removed were small in volume (range 7.5-15.7 mL) and three were larger (range 20.8-39.7 mL). In four cases the endometrial cavity communicated with the tubal lumen, hematometra was present in three cases, and endometriosis was diagnosed in six. In six of the seven rudimentary horns without hematometra, the endometrial mucosa did not correspond to the cycle phase of the endometrium of the hemiuterus; however, in the three rudimentary horns with hematometra, the endometrium presented cycle-phase characteristics similar to those of the hemiuterus. The endometrio-myometrial junction, the underlying myometrium, and the arcuate arterioles were always altered. We consider that the absence of cyclic changes in the endometria of the smaller horns may be attributed to reduced vascular supply, to the absence of any isthmocervical structure, and to the qualitative and/or quantitative differences in endometrial mucosal receptors.