Pathology in practice: pituitary adenoma in a sheep

Authors: Smith, Jodi; HARM, TYLER - Iowa State University; Greenlee, Justin

Submitted to: Journal of the American Veterinary Medical Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2017
Publication Date: 4/1/2019
Citation: Smith, J.D., Harm, T.A., Greenlee, J.J. 2019. Pathology in practice: pituitary adenoma in a sheep. Journal of the American Veterinary Medical Association. 254(7):819-821. https://doi.org/10.2460/javma.254.7.819.
DOI: https://doi.org/10.2460/javma.254.7.819

Interpretive Summary: Tumors of the pituitary gland are rare in domestic animals. This report describes a pituitary mass in a Suffolk sheep that was diagnosed as a pituitary adenoma and was associated with clinical signs of infertility. Veterinary laboratory diagnosticians, practicing veterinarians, and students of veterinary pathology will use this case report to better understand tumors of the pituitary gland and potential causes of infertility in sheep.

Technical Abstract: A 5-year-old Suffolk ewe maintained as breeding stock in the scrapie-free flock at the USDA National Animal Disease Center was euthanized and presented for necropsy because of poor reproductive performance. The ewe produced 5 lambs in 3 prior lambings, but failed to carry lambs to term in her 4th season. The ewe had been exposed to a ram for 40 days during the breeding season and records reflected that she had been observed being bred, however, she either failed to become pregnant or to carry lambs to term. On midsagittal sectioning of the head, a 3 cm x 4 cm x 3 cm, irregular, mottled tan-red mass was detected within the pituitary fossa, expanding the pituitary gland, enlarging the sella turcica, and elevating and compressing the hypothalamus, thalamus, and midbrain. Other changes observed on postmortem examination included bilaterally small ovaries lacking grossly visible follicles and corpora hemorrhagica or lutea, consistent with inactive ovaries. The microscopic appearance of the mass was consistent with pituitary adenoma, and the majority of neoplastic cells exhibited moderate to intense cytoplasmic immunoreactivity for prolactin. Based on histologic characteristics of the neoplastic cells and lack of features of malignancy such as vascular invasion, we diagnosed the lesion as a pituitary acidophil adenoma. Pituitary neoplasms in domestic animals are uncommon but are most often reported in dogs and horses. Pituitary tumors should be considered in the clinical differential diagnoses list for small ruminants with reproductive dysfunction and/or inappropriate lactation.