Incomplete Müllerian duct fusion and canalizing.
Keywords: luteolysis, segmental aplasia, bovine, cervix, mucometra, infertility
A fascinating tract, no doubt from a heifer culled for infertility.
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This tract shows two principal abnormalities. The first is partial aplasia of both uterine horns. However, this aplasia was not in the form commonly encountered, where a segment of one uterine horn is missing. Instead, the Müllerian (paramesonephric) tubes had never canalized to form uterine horns except for a segment in the right Müllerian tube. In that region, a substantial lumen had formed and the uterus contained clear mucoid fluid. The ovaries appeared to be normal and functional, a recent ovulation having occurred from the right ovary.
The ability of the uterus to produce sufficient amounts of prostaglandin F2 alpha (PGF) to cause luteolysis was of particular interest. In that regard, readers will recall that luteolysis in ruminants depends on production of PGF by the endometrium in the uterine horn ipsilateral to the corpus luteum (CL). In the left ovary of this specimen, there was a small corpus albicans, suggesting that the left uterine horn had indeed produced enough PGF to bring about luteolysis. Yet, there was no apparent lumen in that horn, so the question arises: Were there endometrial mucosal fragments in that horn, not visible to the author?
It is possible that luteolysis could have occurred by slow (degenerative?) luteolysis in the left ovary. This is known to occur in cattle with complete absence of one uterine horn. In other words, cows or heifers with ovulations ipsilateral to completely aplastic uterine horns do not experience interminable luteal phases.
The second feature of this tract that was particularly interesting was the complete separation of the two uterine horns, including it would appear, their cervixes as well. This is akin to the situation in lagamorphs (rabbits and hares) where the two Müllerian tubes only fuse distal to the cervixes. That is referred to as uterus didelphys (< Gr Delphus meaning womb.). In cattle, it is not rare to encounter two separate or partially fused cervical canals within a large cervical body or even bands of incomplete fusion of the Müllerian system in the vagina but a situation where there are two completely separate Müllerian tubes is indeed rare. Unfortunately the vagina of this specimen was unavailable; it would have been fascinating to see if the cranial vagina (also part of the Müllerian system) was completely separate as well.
