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Feline Pituitary Adenomas

Miller MA, Piotrowski SL, Donovan TA, Scott-Moncrieff JC, Owen TJ, McCue JP, DuSold DM, Ramos-Vara JA, Weng HY, Chen AV, Martin LG, Bruyette DS. Feline Pituitary Adenomas: Correlation of Histologic and Immunohistochemical Characteristics With Clinical Findings and Case Outcome. Vet Pathol. 2020 Dec 7.

Acromegaly is an increasingly recognized disorder of cats caused by a secretory adenoma in the pituitary gland (somatotroph) which produces an excess of growth hormone. Traditionally this condition leads to diabetes mellitus, enlarged head and paws, cardiac disease, and bone alterations. However, recent data has suggested many signs may be more subtle and in some cases limited to diabetes mellitus. Other tumors and hyperplastic conditions of the pituitary have also been recognized, many of which are subclinical. There is, however, a lack of good data on the prevalence, immunohistotype, and prognosis of pituitary disease in cats.

The purpose of this study was to determine the prevalence of pituitary lesions in cats and to correlate immunohistochemical features of feline pituitary adenomas with clinical findings and outcomes. The study was designed as a retrospective observational study in two parts: the first involved reviewing records of cats undergoing post-mortem exam who had their pituitary examined; the second involved the additional review of hypophysectomy specimens submitted from the Animal Medical Center. Only post-mortem specimens were included in the prevalence portion of the study.

Histologically, pituitaries were divided into normal, hyperplasia, adenoma, cysts, or miscellaneous lesions. Histochemically, masses were described at acidophilic, basophilic, or chromophobic. IHC stains were performed for growth hormone (GH), ACTH, MSH, prolactin, FSH, LH, and TSH.

For the prevalence section, 141 cases met inclusion criteria, of which 36 had lesions. Thirteen of these were adenomas, 13 hyperplasia, 5 lymphoma, 1 ependymoma, 2 FIP, and 3 cysts.

Hyperplasia was only associated with clinical disease in one cat (with hypersomatorophism), compared to 12 of 13 cats with adenomas.

Forty-four pituitary tumors from 43 cats underwent full IHC panels. 20% adenomas were somatotrophs (46%), 11 melanotrophs (25%), 11 gonadotrophs (25%), and 2 thyrotrophs. Lactotrophs were not identified. One cat had a double adenoma but no plurihormonal tumors were identified.

Hypersomatotropism was diagnosed in 16 of the 20 cats with somatotroph adenomas and none of the other cats. Hypercortisolism was diagnosed in 5/11 cats with melanotroph adenoma. Hypergonadotropism was not diagnosed in any cat, but 4 cats with gonadotroph adenoma had neurologic disease. 17/20 cats with somatroph adenomas and 6/11 cats with melanotroph adenomas had diabetes mellitus.

The authors conclude that hypophysectomy improves the survival of cats with pituitary adenomas. Somatroph adenomas are most common, followed by MSH/ACTH secreting tumors.

Several limitations were present to this study. The post-mortem portion was performed on cats already undergoing necropsy at a teaching hospital, who as such may have had a higher prevalence of disease states than the general population; further, those cats who hard their pituitary examined may have had a greater suspicion of pituitary lesions. The antemortem samples were recruited form a single center, and as such may not reflect regional or institutional differences.

Overall, this study suggests that hyperplastic and adenomatous pituitary disease is relatively prevalent in the feline population, and presents relevant information on the cell type of origin of most tumors. It suggests that most adrenocorticotrophic tumors are likely MSH and ACTH dual-secreting rather than solely corticotrophs, and that lactotrophs are very uncommon. Finally, it suggests that for cats with clinical signs attributable to pituitary growths, trans-sphenoidal hypophysectomy is associated with a greater survival than medical management. Further work into the distribution of disease and prognosis is needed to provide more information on these conditions. (MRK)

See also:

Coster C, Fenn J, Glanemann B, et al. A retrospective study on hypophysectomy in feline acromegaly. In: British Small Animal Veterinary Association Congress Proceedings; 2020;408.