Histopathological Characteristics of Endometrosis in Thoroughbred Mares in Japan: Results from 50 Necropsy Cases

Abstract

Uteri from 50 necropsied nonpregnant Japanese Thoroughbred brood mares (1–30 years of age) were investigated to clarify the histopathological characteristics of endometrosis in Japanese Thoroughbred mares and the distribution pattern of endometrosis lesions in the uterus as a whole. Endometrosis was observed in all animals over 6 years of age and in all of the 21 mares aged over 12 years of age. The affected mares showed elastofibrosis of arteries, veins and lymphatic vessels in the uterine wall, atrophy of the uterine smooth muscle layers and hyperplasia of collagen fibers among the smooth muscle fascicles of the myometrium, in addition to pathomorphologic features of endometrosis such as stromal endometrial fibrosis accompanied by endometrial atrophy, periglandular fibrosis and reduction of uterine glands. The severity of the histopathological changes increased with advancing age. Lymphatic vessels with elastofibrosis showed marked lymph congestion, leading to lymphatic edema. With increasing age, the extent of the distribution of these lesions tended to expand from focal to diffuse involvement of the entire uterus. Based on these findings, we speculate that aging plays a role in the pathogenesis of endometrosis; circulatory disturbances due to intrauterine angiosis or angiopathy, particularly reduction of the arterial blood supply and disturbance of venous drainage, resulting in a reduction of lymphatic drainage (lymphatic edema), are closely related to the onset and progression of endometrial fibrosis and myometrial atrophy with fibroplasia may result in myometrial hypofunction during the peri-implantation or puerperal period.

Strain-specific induction of endometrial periglandular fibrosis in mice exposed during adulthood to the endocrine disrupting chemical bisphenol A

“…The decreased reproductive efficiencies and loss of fertility caused by equine endometrosis in mares suggests that the endometrosis-like phenotype may play a role in the decreased average litter size characteristic of C57Bl/6N (6.5 pups) compared to CD-1 mice (11 pups) [35, 78]. Whereas age is the most important factor related to onset of equine endometrosis in mares [36, 39], the observed increases in density and incidence of gland nests, as well as increased periglandular fibrosis resulting from BPA exposure in both strains of mice suggest that genetic and endocrine disruptive effects contribute to alterations in stromal collagen accumulation and the development of endometrosis.…”

“…In addition to being associated with pathology of the human uterus, dysregulation of collagen accumulation and excessive fibrosis is a hallmark of equine endometrosis, one of the most important causes of infertility in mares [34]. Equine endometrosis is an age-related and irreversible degenerative disease of the uterus characterized by markedly increased endometrial stromal and periglandular fibrosis (EPF) associated with “gland nest” structures and is unrelated to human endometrioses [35–39]. The severity of EPF is inversely correlated to successful conception and gestation and is associated with increased rates of embryonic or fetal foal loss and increased susceptibility to infection [37].…”

IIB or not IIB, part 1: retrospective evaluation of Kenney–Doig categorization of equine endometrial biopsies at a veterinary diagnostic laboratory and comparison with published reports

“…It is well established that the incidence of endometrial fibrosis increases as mares age. 9,[11][12][13]16,18,32,45 Mare populations that consist predominantly of older animals may therefore be expected to have a higher incidence of endometrial fibrosis and more severe Kenney-Doig categories. One retrospective analysis was conducted on 816 biopsies submitted from exclusively mares that were ≥20-y-old.…”

Endometriosis in Mare; What the Mare Can Teach Us When Dealing with Endometriosis in the Woman

“…A grading system came into effect in the late 1980s [12]; this was later modified by Schoon [12,13]. Currently endometriosis is defined as active or inactive periglandular and/or stromal endometrial fibrosis including glandular alterations within fibrotic foci [14]. Single glands and/or glandular nests may be affected in equine edometriosis [15,16].…”