Ruiz‑Riera et al. Porc Health Manag (2021) 7:58 https://doi.org/10.1186/s40813-021-00237-8 CASE REPORT Open Access A case of uterine inclusion cysts in a sow Elisa Ruiz‑Riera1, Miquel Nofrarias3,4, Bernat Martí‑Garcia1, Mariano Domingo1,2,3, Joaquim Segalés1,2,3 and Enric Vidal3,4* Abstract Background: Serosal inclusion cysts are thin walled-structures located on the peritoneal surface of the uterus, frequently observed as multiple cystic structures in aggregates or grape-like clusters containing a clear, non-viscous fluid. In human and veterinary medicine, they are thought to be developed under hormonal effects, or after manipu‑ lation or inflammation of the reproductive tract. However, they have not yet been described in swine. Case presentation: A uterus of a 3-year-old crossbreed sow was condemned at slaughter due to the presence of multiples cystic cavities attached to the serosal surface. Microscopically, multiple cystic dilations emerging from the serosa were lined by a simple and flattened epithelium (cytokeratine positive and vimentin negative on immunohis‑ tochemistry) supported by a subepithelial layer of collagen. Grossly and histologically, they were diagnosed as serosal inclusion cysts. Conclusion: To the authors’ knowledge, this report represents the first description of serosal inclusion cysts in sows. These lesions should be taken into consideration within the differential diagnostic list of cystic peritoneal lesions such as cystic neoplasms, congenital cysts, and parasitic diseases. Keywords: Serosal inclusion cysts, Uterus, Reproductive tract, Swine Background In human obstetrical literature they are known as peri- Serosal inclusion cysts are thin-walled structures located toneal inclusion cysts because are often observed in peri- on the peritoneal surface of the uterus, frequently shown toneum affecting mostly uterus, but also other abdominal as multiple cystic structures in aggregates or grape-like organs. Although aetiology is not well understood, some clusters containing clear non-viscous fluid [1, 2]. In the studies suggest that they are developed under hormonal veterinary literature there are scant references regard- effects. Management options in women patients include ing this cyst type, with cases described mostly in the dog from observation and follow-up of the patient to ovario- [3, 4], but also in other species such as cats or ruminants hysterectomy [8]. (including one publication in buffaloes) [2, 5, 6]. Cysts This report describes, for the first time in the porcine are attached to the anti-mesometrial side and are mainly species, the gross pathology and histology of uterine described in the female dog during the postpartum inclusion cysts in a sow. period but have also been described in cases with pyome- tra. This is considered an incidental finding in this animal Case presentation species [1, 7]. During routine swine post-mortem examination at slaughterhouse, a uterus of a 3-year-old crossbreed sow was condemned due to the presence of multiple cystic *Correspondence: enric.vidal@irta.cat cavities attached to the serosal surface. Cysts were vari- 3 OIE Collaborating Centre for the Research and Control of Emerging able in diameter (from 0.5 to 5 cm) and were filled with and Re-Emerging Swine Diseases in Europe (IRTA-CReSA), Bellaterra, transparent fluid (Fig. 1a,b). Barcelona, Spain Full list of author information is available at the end of the article © The Author(s) 2021. 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The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​ mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Ruiz‑Riera et al. Porc Health Manag (2021) 7:58 Page 2 of 4 Fig. 1 Macroscopic and microscopic findings. a Gross image of the sow uterus, with multiple cystic structures of variable diameters attached to the serosa. b Detail of the cysts. Notice the transparent wall and clear fluid that fills the cysts. c Histologically, cysts were lined by a simple and flattened epithelium with no atypia, with the lumen filled with hyaline proteinaceous material (corresponding to fluid). The subepithelial lamina consisted mainly of collagen fibres. Insert: detail of the cysts lining epithelium. Externally, cysts are also lined by peritoneal epithelium. H&E. × 5 and insert × 80 Samples were submitted to the Slaughterhouse Sup- examination were obtained and stained with haematoxy- port Network (Servei de Suport a Escorxadors [SESC] lin and eosin. Also, immunohistochemical techniques to IRTA-CReSA]) [9] to rule out a presumptive diagnosis of detect cytokeratin and vimentin intermediate filaments multiple Cysticercus tenuicollis cysts or other potential were performed on the studied samples to confirm or lesions compatible with zoonotic pathogens. A container rule out the epithelial or mesenchymal origin of the cysts’ with formaldehyde (10%) was received with a 9 cm in cell covering layer, respectively. length piece of uterus with multiple serosal cysts of 0.3 Histological examination revealed multiple cystic dila- to 2 cm diameter. Sections were made and embedded in tions emerging from the uterus serosa that were lined by paraffin blocks. Subsequently, sections for histological a simple and flattened epithelium, with no cellular atypia. Ruiz‑Riera et al. Porc Health Manag (2021) 7:58 Page 3 of 4 Externally and concurrently, the cysts and the uterus were As pigs are progressively becoming pet animals, life recovered by an also simple and flattened epithelium corre- expectancy lengthens, with more reproductive tract dis- sponding to the peritoneum. The subepithelial lamina con- turbances reported as it happens in the feline and canine sisted mainly of collagen fibres. In the union between the homologues [1]. In a recently published case series of pet cysts and the uterus, normal smooth muscle fibres with no adult female pigs [12], cystic endometrial hyperplasia was pathological alterations were also observed (Fig. 1c). Immu- a common finding as well as uterine tumours detected nohistochemistry revealed that the epithelium on both sides during ovariohysterectomy or at necropsy. Tumours of the cyst walls was positive to cytokeratin and negative to identified were leiomyoma, fibroleiomyoma and leiomyo- vimentin, suggesting a mesothelial origin (Fig. 2). Histologi- sarcoma [11]. cal findings were consistent with serosal inclusion cysts. Serosal inclusion cysts are occasionally described in the veterinary literature, mostly in dogs and cats [1, 3–5, 7]. Discussion and conclusions Lesions are located on the surface of the uterus, and it is There are few publications regarding benign and malignant hypothesized that they develop in areas with mild perito- neoplastic lesions found in the reproductive tract of sows. neal reactivity, which may cause entrapment of small areas In a recently published review from carcass inspection in of serosa. Subsequent eventual secretions of this serosa domestic pigs [10], the most frequently reported lesions of produce very thin-walled cysts that emerge and protrude the reproductive tract in the sow were leiomyoma, fibroma, from the surface into the peritoneal cavity. Cysts may be cystadenoma, fibroleiomyoma and carcinoma, with occa- single or multiple, and frequently occur in clusters on any sional metastatic lymphomas described. No inclusion cysts area of the peritoneum covering the uterine horns or body. have been reported so far in swine [10, 11]. They are referred to contain clear, non-viscous fluid. These lesions are commonly seen in bitches following caesarean section, where the uterus has been previously handled and manipulated or in post-partum uterine involution [1, 2]. In the human literature, multiple denominations are used for the same finding, being peritoneal inclusion cysts the most frequently used terminology, but also, they have been referred as benign (multi) cystic peritoneal mesotheliomas, inflammatory cysts of the peritoneum, postoperative peritoneal cysts, and benign papillary peri- toneal cystosis. The aetiology and pathogenesis are not well understood but, in all cases described, the patients have a clinical history of women of reproductive age with abdominal or pelvic surgeries, or inflammation in the abdominal cavity or reproductive tract. Evidence suggests that hormone shifts influence the course of the disease. Management options range from observation and follow- up of the patient to surgical resection of the reproduc- tive tract. Cure is thought to be achievable with surgical resection only [8]. No apparently vital implication occurs for women, female dogs nor cats. Since the current case is the first description of serosal inclusion cysts in swine to the authors’ knowledge, prob- ably it is a very uncommon incidental finding at slaugh- ter. However, no clinical signs are expected in affected animals, since it is a non-infiltrating but a soft com- pressing structure into the abdomen. Therefore, it is also probable that veterinarians, at abattoir or also during a necropsy, may just overlook or minimise the importance of this finding in the eventuality of being present. On the Fig. 2 Immunohistochemical characterization. a Both the inner other hand, there are other conditions implying cysts in and outer epithelium (arrows) were positively stained with pan-cytokeratin antibody, the immunolabeling was more intense at the reproductive tract of the sow. Epithelial neoplasms of the base of the cyst and more faint as the epithelium flattened. b The the ovary must also be considered. An ovarian papillary epithelium was negative to vimentin immunolabeling cystadenocarcinoma has been described with multiple Ruiz‑Riera et al. Porc Health Manag (2021) 7:58 Page 4 of 4 clustered fluid filled cystic lesions of variable diameters Consent for publication Not applicable. throughout the abdominal serosa [10]. Another pos- sible differential diagnosis with cystic implication in Competing interests abdominal surfaces is congenital serous cysts. These The authors declare that they have no competing interests. latter cysts are attached to the capsule of the liver and Author details have been reported in many different species, including 1 Servei de Diagnòstic de Patologia Veterinària (SDPV), Departament de Sanitat swine, and are considered rare incidental findings dur- i d’Anatomia Animals, Universitat Autonòma de Barcelona, 08193 Bellaterra (Cerdanyola del Vallès), Barcelona, Spain. 2 UAB, Centre de Recerca en Sanitat ing laparotomies or necropsies. Congenital serous cysts Animal (CReSA, IRTA‑UAB), Campus de la Universitat Autònoma de Barcelona, are usually small and multiple, but can be isolated and Barcelona, Spain. 3 OIE Collaborating Centre for the Research and Control grow extremely large and become symptomatic [13–15]. of Emerging and Re-Emerging Swine Diseases in Europe (IRTA-CReSA), Bel‑ laterra, Barcelona, Spain. 4 IRTA, Centre de Recerca en Sanitat Animal (CReSA, Parasitic diseases can also cause cystic formations affect- IRTA‑UAB), Campus de la Universitat Autònoma de Barcelona,, 08193 Bellaterra ing serosal surfaces. Cysticercus tenuicollis cysts (Tae- (Cerdanyola del Vallès), Barcelona, Spain. nia hydatigena larval stage) are shown as transparent Received: 13 August 2021 Accepted: 19 October 2021 vesicles on the surface of the liver, omentum, or other abdominal viscera. Cysticerci are subspherical, whitish, translucent, fluid‐filled cysts about 1 cm in diameter. 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