History
A 16-year-old 450-kg Italian Saddle Horse maiden mare, retired from sport activity for over a year, was evaluated for monitoring of the estrous cycle for breeding purposes. The mare was housed in an individual paddock (10 X 10 m), was fed with polyphyte hay, and had water access ad libitum. No abnormalities were observed at clinical examination. During reproductive soundness evaluation, the conformation of the perineal region was found to be clinically normal. Transrectal palpation of the cervix, uterus, and right ovary revealed no abnormalities. However, transrectal palpation revealed an enlarged left ovary with irregular shape, surface, and consistency.
Question
What are key differential diagnoses that could have caused the abnormalities of the left ovary?
Answer
The differential diagnosis list for unilateral ovarian enlargement should include nonneoplastic conditions, such as anovulatory follicle, ovarian hematoma, and abscess, as well as neoplastic conditions, such as teratoma, granulosa, and theca cells tumors.
Results
Transrectal ultrasonography of the mare’s reproductive tract was performed immediately after clinical examination and then every 5 days for the following 20 days with the use of a 7.5-MHz linear probe (Sonosite Micromaxx; FUJIFILM Sonosite Inc). At the first examination, the cervix and uterus had neither cysts nor edema, and the right ovary had no follicle > 25 mm diameter and no corpus luteum. The left ovary had a corpus luteum surrounded by a heterogeneously echoic mass structure (Figure 1). Transrectal palpations and ultrasonographic examinations were performed over a 40-day period, during which the complex mass persisted unmodified. On the basis of ultrasonographic findings, our differential diagnosis list included anovulatory follicle (hemorrhagic, luteinized), neoplasia (teratoma, granulosa theca cell tumor), or ovarian abscess.
Ultrasonographic image of the left ovary of a 16-year-old 450-kg Italian Saddle Horse maiden mare evaluated for monitoring of the estrous cycle for breeding purposes. Notice the presence of corpus luteum (asterisk) surrounded by hypoechoic (dotted outline) and hyperechoic (arrowheads) areas.
Citation: Journal of the American Veterinary Medical Association 260, 11; 10.2460/javma.22.04.0186
The mare was treated with a single injection of cloprostenol (250 μg, IM, once) to promote the onset of estrous, which happened 3 days after administration of this prostaglandin. During estrous, the mare underwent natural cover at days 3, 5, and 7 until ovulation verified by ultrasound examination. At day 11, the presence of 2 embryonic vesicles (7 and 5 mm in diameter) were identified with transrectal ultrasonography, and early pregnancy was diagnosed.
Discussion
According to clinical and ultrasonographic findings for the mare of the present report, the differential diagnosis for unilateral ovarian enlargement should include both neoplastic and nonneoplastic conditions. Anovulatory follicle is the primary cause of ovarian enlargement1 and in the present case was ruled out because the ultrasonographic monitoring of the complete estrus cycle demonstrated that the mass did not change over time. In addition, the ultrasonographic appearance of anovulatory follicle did not match the case herein described. The mass was not compatible with ovarian hematoma, which is ultrasonographically characterized by an initially hypoechoic blood-filled cyst that modifies into a mottled appearance (when the blood clot matures) and then returns to clinically normal size and echogenicity.2 Ovarian abscess is commonly differentiated from other ovarian conditions thanks to its ultrasonographic appearance, which usually presents a homogeneous hyperechoic content surrounded by a thick wall.3 Despite rare, ovarian neoplasm (like teratoma, granulosa, and theca cells tumors) should be always considered as differential diagnoses in mares when transrectal examination reveals unilateral ovarian enlargement and ultrasonography shows an ovarian structure that is large, has a mixed echogenic pattern, and is a capsuled structure.4,5
Outcome
Two days after pregnancy diagnosis, the mare died because of colic. At necropsy, the ovaries were collected for analysis. At gross examination, the left ovary was firm, multinodular, and 5.5 X 3.0 X 3.5 cm (Figure 2). On cut section, the left ovary had a large cyst that exuded moderate amount of tan fluid with brownish clumped material. Histologically, the left ovary was characterized by the presence of an unencapsulated, demarcated, densely cellular, multilocular neoplasm, which effaced the normal ovarian architecture and compressed the rare residual ovarian follicles, surrounded by areas of mesenchymal cell proliferation (thecal-like). The neoplasm consisted of a tissue with large areas representing 3 primordial germ lines: 1) ectodermal elements consisting of neural tissue and a cystic structure that was lined by stratified squamous epithelium with gradual keratinization, had a large lumen filled with keratin, and was surrounded by sebaceous glands; 2) endodermal elements represented by well-differentiated lobules of the thyroid gland consisting of many colloid-filled follicles, respiratory epithelium, and renal parenchyma; and 3) mesodermal elements consisting of mature cartilage, trabecular bone with bone marrow, and bundles of smooth muscle tissue. According to histological findings, a definitive diagnosis of ovarian teratoma was made, and these findings were consistent with findings on ultrasonography, during which different echogenicity patterns were detected that related to the presence of bony material (hyperechoic areas) and hair or keratinized material (linear echogenic shadow lines) within the mass.
Postmortem gross and photomicrographic images of the left ovary of the horse described in Figure 1. A—The external surface appears irregular and multinodular. B—On cut surface, a large cyst contains clumped brownish debris and pink solid nodular areas. C—A cystic structure is lined by stratified keratinizing epithelium, and the lumen is filled with keratin. H&E stain; bar = 200 µm. D—Mesenchymal elements shown include hyaline cartilage surrounding trabecular bone filled with bone marrow. H&E stain; bar = 200 µm.
Citation: Journal of the American Veterinary Medical Association 260, 11; 10.2460/javma.22.04.0186
Acknowledgments
No third-party funding or support was received in connection with this case or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
References
- 1. ↑
McCue PM. Tumour, or not tumour, that is the question. Equine Vet Educ. 2013;25(1):11–14. doi:10.1111/j.2042-3292.2012.00404.x
- 2. ↑
Cuervo-Arango J, Newcombe J. Ultrasound confirmation of ovulation in mares: a normal corpus luteum or a haemorrhagic anovulatory follicle? Reprod Domest Anim. 2013;48(1):105–111. doi:10.1111/J.1439-0531.2012.02039.X
- 3. ↑
Ramirez S, Sedrish SA, Paccamonti DL, French DD. Ultrasound as an aid for diagnosis of ovarian abscesses in two mares. Vet Radiol Ultrasound. 1999;40(2):165–168. doi:10.1111/J.1740-8261.1999.TB01903.X
- 4. ↑
Catone G, Marino G, Mancuso R, Zanghì A. Clinicopathological features of an equine ovarian teratoma. Reprod Domest Anim. 2004;39(2):65–69. doi:10.1111/j.1439-0531.2003.00476.x
- 5. ↑
Lefebvre R, Theoret C, Doré M, Girard C, Laverty S, Vaillancourt D. Ovarian teratoma and endometritis in a mare. Can Vet J. 2005;46(11):1029–1033.
