If infection continues, lymphocytes are usually the prominent cell type, activation of fibroblasts takes place, and there is laying down of fibrous tissue around the blood vessels and glands. Fibrosis - Stromal cells of the lamina propria do not normally form collagen. However, they do have the ability to produce collagen. Endometrial fibrosis is a result of continued irritation by infectious agents, as well as other stimuli. Fibrosis begins by being laid down around blood vessels and around endometrial glands.
Fibrosis spreads throughout the stratum compactum and stratum spongiosum.
Atrophy - Endometrial atrophy is a feature of seasonal anestrus. It is also caused by ovarian inactivity and is often seen in aged mares with poor ovarian activity or in the final stage of fibrosis when the glands are all lost. The earliest attempt to classify the degree of damage to the endometrium was by Kenny. In 1986, Kenny and Doig collaborated on a classification method, which standardized the interpretation of equine endometrial biopsy. A Category B Category C Category D Kenny Category I Category IIa Category IIb Category III Category I - Normal endometrium with no pathologic changes or existing changes are slight and sparsely scattered.