Specific description of cases of proliferative lesions of endometrial glands with different forms of the disease is not easy and often misleading. In addition, the physiology of the reproductive cycle, during which the endometrium of bitches is subject to dynamic reconstruction, does not make the task easier. The research presented recognizes changes in the macroscopic and microscopic image of the endometrium observed in the disease known as CEH-P complex.
De Bosschere et al.  points to the importance of research in the pathological diagnosis of the diseases of the uterus in female dogs. According to the author, a very frequent mistake encountered while making definitive diagnoses of specific diseases of the reproductive system is that vets only clinically assess the state of the organ, but this assessment is not accompanied by detailed research. In women, histopathological examination is the golden rule in the diagnosis of diseases of the uterus [29, 35]. In such cases, an abnormal bleeding or a suspected infertility are the indicators for advanced diagnostics. It is a routine test in the case of a chronic inflammation of the lining of the uterus, and the identification of plasma cells in the endometrial stroma provides the basis for a diagnosis .
Lesions involving the uterus were classified according to the severity of CEH-P. In the macroscopic and microscopic assessment of the uterus of a bitch with a significant advancement of the disease, the changes typical of classical pyometra were noted. The significant enlargement of the organ, congestion and thickening of the endometrium as well as residual purulent exudates in the lumen of the uterus were observed. Microscopic examination of the sections of the uterine horns showed structural changes typical of CEH, including proliferation, together with the presence of cysts on the surface of the endometrium (Figure 4B, C). In addition, the proliferation of the endometrial epithelial lining was observed as well as the transformation of the endometrial glandular epithelium (secretory phase).
The results presented in this study as well as the authors cited for all cases of the analyzed uteri, describe a considerable degree of endometritis, mainly purulent. Inflammatory infiltration, primarily of mononuclear cells, demonstrating a chronic (100% of cases per group), inflammatory process was identified within the endometrial stroma. However, on the mucosal surface and in the lumen of the uterine glands a plurality of neutrophils was observed (Figure 4 C). In addition, though rare, there were cases of moderate to significant degrees of, mostly, multifocal fibrosis (16,7%) and endometrial haemorrhage (13,3%).
A picture typical of CEH-P was also observed by Groppetti et al. . Apart from cystic and inflammatory processes, instances of CEH-P were accompanied by swelling of the endometrial stroma, infiltration of inflammatory cells and mucosal haemorrhage, which has also been described in this research.
The research findings by Younis, et al.  also confirm the existing changes in the macroscopic and microscopic image observed in this study. In the group of uteri affected by CEH-P, the authors chose three characteristic histological changes typical of the disease. The first one included the purulent uterine content, which, in some cases occupied the deeper layers of the uterus. Another one was referred to the changes associated with pathological enlargement and proliferation of endometrial glands (CEH). The last, third group of changes included - progesterone dependent - proliferation of glandular epithelium, showing vacuolization of the cytoplasm and a single pyknotic nucleus. To a lesser or greater extent, the observed histopathological changes were also recorded by Bigliardi et al. .
An analysis of the age structure of bitches with particular uterine diseases in our study confirms the development of pyometra occurring more often in older females, aged about - 9.3 years, while CEH – affects bitches over 6 years of age, (p<0,001). Although both diseases are distinct conditions included in the complex pathology of the uterine diseases of bitches, the importance of CEH in the development of pyometra is unquestionable [5, 10, 36].
Relating our own results to the works cited, it should be noted that among the analyzed cases of pyometra, there were also advanced, multifocal cystic hyperplasia of endometrial glands in all of them (100% of cases, Figure 4B, C). The histological picture refers to class VI of the classification of uterine diseases described by de Bosschere et al.  as pyometra (hyperplastic) with severe inflammatory response, numerous cysts, an overstated relation of endometrium to myometrium as well as moderate proliferation of fibroblasts.
Although cystic endometrial hyperplasia glands (CEH) are encountered in both bitches and queens, the disease more often affects the bitches. This is associated with a longer period of impact of progesterone on the endometrium during the diestrus [1, 37, 38]. In the literature, many studies describing abnormal endometrial hyperplasia in relation to diseases like CEH, also mark the likelihood of its progress to life-threatening stages [14, 22, 23, 30, 36-40]. Cysts developing in the endometrium classified as CEH differ significantly in terms of number, size, distribution and histomorphology . Groppetti et al. , in their microscopic evaluation of CEH, observed a clear hyperplasticity and thickening of the tissue with endometrial stromal edema and a significant extension and branching of glands. The diameter of the cysts identified by them amounted to a few millimeters, and the interior was filled with clear secretions of mucous character. Both the superficial and glandular epithelium of the endometrium formed high and irregular stratified columnar cells.
Compatibility of the described results was also achieved in our research; microscopic analysis of histologic preparations of uteri affected by CEH revealed a wide range of observed changes ranging from mild (13,3% cases per group) to advanced (86,7%). The histologic evaluation was dominated by an increase in glands of the endometrium, with the occurrence of both focal and multifocal kinds. In addition, we observed a significant flattening and progressive atrophy of the glandular epithelium as well as the often acute, multifocal haemorrhage of the endometrium (30%), which has not been included in the analyses of the previously cited authors (Figure 3B, C). Using the classification of uterine diseases used by De Bosschere et al. , the presented conversion, which does not include an inflammatory response, is eligible for the third group - described as a severe form of CEH with numerous large cysts and increased relation of endometrium to myometrium.
During the initial evaluation of the research material, the uteri of the bitches from the experimental group I (GI) have been characterized as falling within the range of moderate inflammation. Such a finding is possible thanks to the macroscopic evaluation of the endometrium of clinically heathy bitches in the anestrus phase. A clearly reddened and thickening endometrium, in some cases, with a small amount of serous-bloody discharge, suggested the classic picture of endometritis (Figure 2A). Meanwhile, microscopic research has not confirmed any inflammation of the lining of the uterus, and, what is more, there was no presence of any cells that provide for ongoing inflammatory process within this organ, but only multifocal endometrial haemorrhage (100 % of cases per group) with mild (20%) to moderate (80%) severity (Figure 2B, C). In some cases uteri classified into this group showed a moderate (56,6%) to high (23,3%) degree of endometrial edema, occurring uniformly within the tested section of the horn. The results obtained by our studies confirm the need to perform detailed analyses in the differentiation of conditions of the uterus in bitches due to the lack of consistency of macroscopic assessment with histological analysis. The presented results, however, require the continuation of studies and more detailed biological analysis, due to the lack of data clarifying the described condition.
As indicated by published literature, the clinical condition of the patient does not constitute grounds for the exclusion of uterine diseases [1, 2, 10]. The obtained studies reported that the majority of bitches, which were classified as clinically healthy, were found to have uterine or ovary disorders in varying degrees of progression. In De Bosschere et al.  this problem concerned 20 out of 26 patients identified as having hyperplastic changes of the endometrium from mild (8) to heavy CEH (9) - both in the diestrus and anestrus phase. Additionally, in some cases, stromal edema, endometrial haemorrhage and local endometrial bleeding was diagnosed. These results are consistent with our own observations, where the majority of cases of haemorrhage of the endometrium and hyperplasia of glands, occurred in clinically healthy bitches who had undergone ovariohysterectomy for the purpose of reducing the risk of later development of uterine diseases and depression of fertility.