Microscopic insights into cervical pathology of canine pyometra

Introduction

Although hormonal influences, particularly progesterone and oestrogen, play a central role in the pathogenesis of pyometra, structural and cellular changes in the cervix and uterus determine disease severity and clinical presentation. Histopathological evaluation provides critical insights into these tissue-level alterations, including epithelial integrity, glandular proliferation, stromal remodeling, vascular changes, and inflammatory cell infiltration, which have been reported in canine pyometra lesions (Prasad et al., 2017 and Xavier et al., 2024) [8,11] . Such microscopic examination is essential not only for understanding disease progression but also for identifying potential correlations between cervical patency, uterine pathology, and systemic hormonal status. The disease typically occurs during the luteal phase of the oestrous cycle, when prolonged progesterone exposure predisposes the endometrium to cystic hyperplasia and secondary bacterial infection (Bosschere et al., 2001) [4] . Clinical manifestations depend largely on cervical patency: open-cervix pyometra often presents with vulvar discharge, whereas closed-cervix pyometra may lead to more severe systemic illness due to retained uterine contents (Renton et al., 1993) [9] . Though ovarian steroid hormones, particularly progesterone and oestrogen, play a role in disease susceptibility, structural and cellular changes within the cervix and uterus determine clinical outcome (Blendinger et al., 1997; Kunkitti et al., 2011) [2,7] . Differences between open-and closed-cervix pyometra include variations in epithelial disruption, stromal density, and inflammatory response (Blendinger et al., 1997; Schoon et al., 1992) [2,10] . Despite its clinical importance, comprehensive cervical histopathology in pyometra remains inadequately characterized. This study aimed to evaluate and compare histopathological features of the cervix in open-and closed-cervix pyometra and contrast them with normal dioestrous bitches to elucidate tissue-level determinants of cervical function.

Materials and Methods

Female dogs of various breeds with clinical signs suggestive of pyometra and six healthy dogs in dioestrous phase (Group III, n = 6) presented to University Veterinary Hospitals, Kokkalai and Mannuthy were utilized for the study. Pyometra confirmed bitches were classified into open cervix (Group I, n = 6) and closed cervix (Group II, n = 6) depending on the clinical signs. Laparotomy was performed with the animal positioned in its dorsal recumbence. The samples were collected and preserved in 10 per cent neutral buffered formalin. The tissues were processed by routine paraffin embedding techniques (Sheehan and Hrapchak, 1980) [11] . The paraffin embedded tissues were sectioned at four-micron thickness and stained with haematoxylin and eosin stain (Bancroft and cook, 1995) [1] . The stained sections were subjected to detailed examination under light microscope. The number of neutrophils in the stroma of mucosa was examined microscopically (400x). For each uterine cervix, 3 sections and 5 fields were investigated. The data were analyzed using suitable statistical software (IBM Corp. 2016) [6] and comparisons between groups were performed using a one-way ANOVA model.

Results and Discussion

From the study, it revealed that in normal dioestrous bitches, infiltration of very few inflammatory cells could be noticed. Cervical glands were noticed which had apparently normal lining epithelium (Fig. 1). In open cervix pyometra, the blood vessels were dilated with pooling of blood characterized by presence of large number of leucocytes within the blood vessels and also pavementing of leucocytes on the wall of the blood vessels. These are the changes characteristic of an inflammatory process in that area. Massive infiltration of the inflammatory cells was also observed. The cervical glands were dilated, hyperplastic and cystic changes noticed. Also, hypertrophy of the muscle fibers were observed. In closed cervix pyometra, scanty infiltration of the inflammatory cells in the sub-epithelial layer could be visualized in the Fig. 2 and3. The cervical glands were apparently normal. Hypertrophy of the muscle fibers were also noticed. The number of neutrophils infiltrated in the stromal layer of the cervix in pyometric dogs and dioestrous dogs were counted, (Table 1). Significant difference was noticed between three groups, Group I was significantly different from Group II & Group III, Group II was significantly different from Group I and Group III, Group III was significantly different from Group I and Group II at five per cent level. The research works pertaining to the histopathological evalution in the cervix of pyometra affected dogs are scarce. A pioneering work by Kunkitti et al. (2011) [7] reported the histopathological changes pertaining to the infiltration of leucocytes in normal and pyometra affected dogs. They reported that neutrophils were the most commonly observed inflammatory cells in the cervix of pyometra affected dogs and subepithelium contained more leukocytes than other layers. The observations of this study correlate with reports of Kunkitti et al. (2011) [7] who observed more neutrophil inflitration in open pyometric dogs when compared to closed pyometric ones, which might have triggered structural changes in cervix and influenced its patency. (Cawston, 1996; Winkler et al., 1999) [5,13] stated that the degree of cervical relaxation in women, was linked with the level of neutrophil infiltration, which could generate collagenolytic enzymes viz., proteases and metalloproteinases. The rise in collagenase enzyme would lead to huge turnover of collagen and deprivation of recently synthesized collagen, which resulted in decreased collagen content in the cervical area of remodeling. Corroborative to the observations of this study, indicating increased neutrophil infiltration in the cervix of open pyometra dogs in comparison to closed pyometra dogs, Kunkitti et al. (2011) [7] also reported that, in open-cervix pyometric dogs more neutrophil infiltration was noticed than closed pyometric dogs, both during anoestrous and dioestrous stages. However, in pyometric dogs, they observed more neutrophils and plasma cells in the vaginal part of the cervix than uterine part which had more inflammatory cells. Also, Tamada et al. (2012) [12] stated that on histopathological examination of pyometric cervix, patency of cervix was directly proportional to neutrophilic count infiltrated in the uterine cervical tissue. Histopathological observations of hyperplastic changes of the cervical glands in cervix of both open and closed cervix pyometra dogs also finds agreement with Bosschere et al.( 2001) [4] who opined that in pyometric bitches, histopathology of the uterine cervix was similar to that of ones with severe Cystic endometrial hyperplasia. Closed-cervix pyometra demonstrated comparatively scant inflammatory infiltration with relatively preserved glandular structure. A significant difference in neutrophil infiltration among the groups highlights the close association between inflammatory cell infiltration and cervical patency. These findings suggest that cervical patency in canine pyometra is primarily influenced by local inflammatory-mediated tissue remodeling rather than hormonal factors alone, underscoring the importance of histopathological evaluation in understanding disease progression and clinical manifestation.

Acknowledgement

AcknowledgementThe author expresses sincere gratitude to Dr. C. Jayakumar for his valuable guidance, to Dr. Latha C., Dean, COVAS, Mannuthy, for providing essential research facilities, and to KVASU for the assistantship and fellowship support.

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