History
An 8-year-old 47-kg (103.4-lb) nulliparous sexually intact female Vietnamese potbellied pig (Sus scrofa domesticus) was presented to the Michigan State University (MSU) Large Animal Surgery Service for evaluation because of a 30-hour history of tissue protruding from the vulva. In addition, the owners reported that a small amount of tissue had protruded from the pig's vulva after estrus but had resolved uneventfully, the pig had been vaccinated with tetanus toxoid a month before the present examination, and no other changes in the pig's health or behavior had occurred.
On physical examination, the pig had an approximately 8-cm-long piece of tissue that protruded from the vulva (Figure 1). The tissue was irregularly shaped and dark red, with black areas on the perimeter. The remainder of the findings from physical examination were unremarkable.
Photograph of an 8-year-old 47-kg (103.4-lb) nulliparous sexually intact female Vietnamese potbellied pig (Sus scrofa domesticus) evaluated because of a 30-hour history of tissue protruding from the vulva. Dorsal is toward the top of the image.
Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.917
For further evaluation, the pig underwent general anesthesia that was induced and maintained with sevoflurane in oxygen delivered by face mask. Digital vaginal examination revealed that the tissue seen extending from the vulva had prolapsed through the cervix. The tissue was ligated with 2-0 polyglactin 910 suture,a amputated at the level of the external cervical os, and submitted to the MSU Veterinary Diagnostic Laboratory for histologic examination. Abdominal ultrasonography revealed that the uterine wall was markedly thickened and that the lumen had a small amount of fluid (approx 1-cm intraluminal diameter; Figure 2). The pig recovered from anesthesia without complication and was discharged, with results of histologic examination pending.
Transabdominal ultrasonographic image of the uterus of the pig described in Figure 1 showing thickened walls of the uterus (brackets) and accumulation of intraluminal uterine fluid (asterisks).
Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.917
Question
What are your differential diagnoses for this condition? Please turn the page.
Answer
On the basis of ultrasonographic findings and origin of the tissue, the 2 main differential diagnoses were cystic endometrial hyperplasia (CEH) and neoplasia (eg, uterine leiomyoma, uterine leiomyosarcoma, or endometrial carcinoma).
Results
Results of histologic examination of the tissue sample confirmed a uterine origin and supported the diagnosis of CEH; however, neoplasia could not be ruled out. Therefore, the pig was returned to the MSU Large Animal Surgery Service for ovariohysterectomy (OHE) 2 weeks later. Physical examination at the time of readmission revealed a small amount of opaque mucoid discharge around the vulva and perineal region. The remainder of the findings from physical examination were unremarkable, and OHE was scheduled for the following day. Food was withheld from the pig overnight in preparation for surgery.
The next morning, the pig was premedicated with butorphanol (0.2 mg/kg [0.1 mg/lb], IM) and midazolam (0.2 mg/kg, IM). To allow for catheterization of the right auricular vein, anesthesia was induced with sevoflurane in oxygen delivered by face mask. Once the catheter was placed, propofol (1 mg/kg [0.5 mg/lb], IV) and lidocaine (0.8 mg/kg [0.4 mg/lb], IV) were administered, then the pig was intubated. Anesthesia was maintained with sevoflurane in oxygen, and the pig was positioned in dorsal recumbency and aseptically prepared for OHE.
An approximately 10-cm ventral midline incision was made starting from approximately 2 cm caudal to the umbilicus and extending to approximately 2 cm cranial to the pubis. Both uterine horns, both ovaries, and a portion of the uterine body were exteriorized. The uterine horns were substantially enlarged (diameter, approx 6 cm; reference limit, typically < 3 cm in diameter in our experience) and had engorged vasculature (Figure 3). In addition, there was a fleshy stalk of tissue (approx 6 cm in length × 1 cm in diameter) on the serosa of the lateral aspect of the left uterine horn. Because of the engorged vasculature, both ovarian pedicles were ligated and transected with an electrocautery device,b and the device was used for ligation throughout the OHE to minimize hemorrhage. For any hemorrhage not controllable with electrocautery, tissue was ligated with 2-0 polyglactin 910 suture. The uterine body was transected with the electrocautery device, and most of the reproductive tract was removed, leaving the uterine stump and stay sutures. A stalk of endometrium, which looked similar to the prolapsed tissue that had been excised on initial examination, everted from the remaining uterine stump. The everted tissue was ligated with 2-0 polyglactin 910 suture and excised with Metzenbaum scissors. On this endometrial tissue was a piece of white suture consistent with the suture used previously when the prolapsed tissue was removed. The uterine stump was oversewn with size-0 polyglactin 910a suture in a continuous Lembert pattern and then in a continuous Cushing pattern. The abdomen was lavaged with sterile saline (0.9% NaCl) solution, which was then removed with suction. No hemorrhage was identified, a routine 3-layer abdominal closure was performed, and penicillin G procaine (21,000 U/kg [9,545 U/lb], IM) was administered. The pig recovered from anesthesia without complication and was returned to a stall for observation overnight. In addition, amoxicillin–clavulanic acidc (15 mg/kg [6.8 mg/lb], PO, q 12 h for 5 days) and meloxicam (0.3 mg/kg [0.14 mg/lb], PO, q 24 h for 5 days) were prescribed.
Intraoperative image showing the use of an electrocautery device (asterisk) to cauterize and transect the left broad ligament of the enlarged uterus of the pig described in Figure 1. The pig is in dorsal recumbency, and its head is toward the top of the image.
Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.917
The removed portion of the pig's reproductive tract was submitted to the MSU Veterinary Diagnostic Laboratory for evaluation. Grossly, the uterine wall was extremely friable, and numerous edematous and necrotic polyps projected from the endometrium (Figure 4). The serosal polyp identified at surgery contained endometrium, consistent with adenomyosis (the migration of endometrial glands through the myometrium and mucosa; Figure 5). On the basis of this finding and the earlier histologic results for the initially excised prolapsed tissue, the prolapsed tissue was considered to have been a large, necrotic polyp that originated from cystic endometrium, and the final diagnosis was chronic, diffuse CEH with no evidence of neoplasia.
Photographs of the uterine and ovarian tissues removed during OHE of the pig described in Figure 1. A—The uterus is enlarged and friable, and there is a serosal polyp (asterisk) that is approximately 6 cm in length × 1 cm in diameter on the serosa of the lateral aspect of the left uterine horn. B—The endometrium is edematous.
Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.917
Photomicrograph of a tissue section of endometrium from the pig described in Figure 1. There are numerous dilated, unorganized endometrial glands (asterisks) surrounded by fibrous tissue (arrows). H&E stain; bar = 500 μm.
Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.917
Discussion
Cystic endometrial hyperplasia has been reported in women1 and various veterinary species.2–5 Uterine cysts typically arise from the endometrial glandular epithelium but can also originate from the myometrium and serosal surface. Endometrial polyps develop from larger cysts and are a sign of advanced CEH, and CEH leads to infertility by impeding fertilization or attachment of the embryo to the endometrium.2,4 In some species, CEH predisposes affected animals to other uterine conditions, including pyometra and, as reported in swine, neoplasia.2–4
Although proposed factors for CEH vary among species, 2 common factors are nulliparity and older age.2 In women, CEH is associated with hyperestrogenism from treatment with estrogen.1 In pigs, sheep, and cattle, repeated estrus cycles without pregnancy increase the amount of estrogen exposure, which promotes endometrial hyperplasia.3 In dogs, prolonged exposure to high progesterone concentrations after estrogenic priming during their 60-day period of diestrus is associated with the development of CEH.4 Also in dogs, a life-threatening sequela to CEH is pyometra, during which the immunosuppressive effects of progesterone combined with pathological processes induced by CEH provide an environment in which bacteria can thrive during the diestrous period.4
The prevalence of CEH in aged pigs has been reported to be as high as 75% (24/32), with the incidence of neoplastic lesions being as high as 60% (20/32).5 The most common uterine neoplasms in pigs are smooth muscle neoplasms (leiomyoma and leiomyosarcoma) and endometrial carcinoma. A recent retrospective study6 of 108 captive animals in the families of Suidae or Tayassuidae with reproductive tract lesions at a zoological park shows that 32 (30%) had leiomyoma, 4 (4%) had leiomyosarcoma, and 13 (12%) had endometrial carcinoma and that there was a high correlation between the severity of endometrial hyperplasia and endometrial carcinoma.
Although more common in dogs than in pigs, pigs can develop pyometra secondary to CEH.7 Furthermore, a study7 shows that 3 of 5 potbellied pigs with pyometra died, whereas the mortality rate in dogs has been reported as 10% (36/356).8 This difference could be because pigs have greater risks with OHE, including higher body weight, greater amount of subcutaneous fat, older age at OHE, and greater vascularity and friability of uterine tissue.7 In the pig of the present report, the extreme friability of the uterus and engorged uterine vasculature illustrated the importance of careful surgical technique.
A study5 shows that 24 of 32 (75%) miniature pigs that were housed at pig sanctuaries or rescue facilities and underwent OHE had uterine lesions; the investigators reported an association between increased age and uterine lesions. Relatedly, to decrease the risk of developing uterine disease, such as CEH and uterine neoplasia, OHE is recommended in potbellied pigs before 6 years of age.7
It is important to note that the FDA does not distinguish between commercial pigs and potbellied pigs with regard to classification as food-producing animals. As such, potbellied pigs should be considered food-producing animals when prescribing and administering all medications, particularly those used in an extralabel manner. The extralabel drug use prescribed in treating the pig of the present report was in accordance with the AMDUCA, and we used information from the Food Animal Residue Avoidance Databank as a reference when counseling the owner regarding withdrawal periods. Similarly, veterinarians should be aware that although owners of potbellied pigs typically view these animals as pets, it is the legal responsibility of the attending veterinarian to adhere to the AMDUCA, including conveying information about withdrawal periods to the client.
Outcome
Ten months after undergoing OHE, the pig of the present report returned to the MSU Large Animal Medicine Service for a wellness examination and was determined to have been in good health, with no reported adverse effects from OHE.
Acknowledgments
Presented in abstract form at the Annual Conference of the Society for Theriogenology, Savannah, Georgia, July 2019.
The authors declare that there were no conflicts of interest.
Footnotes
Vicryl, Ethicon Inc, Somerville, NJ.
LigaSure, Medtronic, Minneapolis, Minn.
Clavamox, Zoetis Services LLC, Kalamazoo, Mich.
References
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