Feline Pituitary Adenomas: Correlation of Histologic and Immunohistochemical Characteristics With Clinical Findings and Case Outcome

Abstract

Pituitary glands from 141 feline autopsy cases were reviewed histologically. Adenoma and hyperplasia were the most common lesions at 13 cases each. Pituitary adenoma was more likely than hyperplasia to be associated with clinical evidence of endocrinopathy or an intracranial mass ( P < .001). A histochemical and immunohistochemical panel was applied to 44 autopsy- or hypophysectomy-derived pituitary adenomas in 43 cats from 2 diagnostic laboratories. Adenomas were differentiated from hyperplasia by the presence of disrupted reticulin fibers. One cat had a double (somatotroph and melanotroph) adenoma. Twenty somatotroph adenomas consisted of periodic acid-Schiff (PAS)-negative acidophils that expressed growth hormone; 16/20 had hypersomatotropism; 17/20 had diabetes mellitus. Eleven melanotroph adenomas consisted of PAS-positive basophils or chromophobes that expressed melanocyte-stimulating and adrenocorticotrophic hormones; 5/11 had hypercortisolism; 6/11 had diabetes mellitus. Eleven gonadotroph adenomas consisted of PAS-negative chromophobes that expressed follicle-stimulating and/or luteinizing hormones. Two thyrotroph adenomas consisted of PAS-negative basophils or chromophobes that expressed thyroid-stimulating hormone. Pituitary-dependent disease was not recognized in cats with gonadotroph or thyrotroph adenomas. The Ki-67 proliferation index in hypophysectomy specimens was lower in somatotroph than in melanotroph adenomas. Fourteen cats with hypophysectomy-treated somatotroph or melanotroph adenoma had an 899-day median survival time versus 173 days in 17 nonsurgical cases. After adjusting for age, adenoma size and type, hypophysectomized cats had an overall better survival time than nonsurgical cases ( P = .029). The study results underscore the value of hypophysectomy and trophic hormone immunohistochemistry in the treatment and classification of feline pituitary adenomas.

Case Report: Cytologic Description of Somatotroph Pituitary Adenoma in a Cat

“…The cytologic appearance of the tumor exhibited some malignancy criteria such as marked anisokaryosis, prominent nucleoli, and nuclear molding. Despite these features, histological evaluation, in conjunction with CT and postmortem findings, was consistent with the accepted definition of an adenoma ( 9 , 12 ). Cellular features are not a reliable indicator of malignant behavior in these neoplasms ( 12 ).…”

“…Growth hormone immunoreactivity can vary widely in somatotroph adenomas, but the pattern and location of staining similar to that in the control (i.e., relatively weak in both the sample and the control) warranted the interpretation of immunoreactivity. The lack of intact reticulin network was used to differentiate adenoma from hyperplasia, and there was no evidence of vascular, bone, or local invasion or metastasis based on CT, gross postmortem examination, or postmortem histopathology ( 9 ). It is unclear why cytological interpretation in the smear showed cellular features of malignancy while histologically anisocytosis and anisokaryosis were interpreted as mild.…”

“…Growth hormone immunohistochemistry revealed many clusters of cells with faint or weak cytoplasmic immunoreactivity within the neoplasm (Figure 4) similar to that in the control. The cellular architecture based on H&E staining, histochemical and immunohistochemical profile and lack of evidence of invasion or metastasis on histology and clinical imaging resulted in a diagnosis of somatotroph adenoma (9). A week later, during post-surgical hospitalization, the patient's clinical condition worsened, and it died.…”

“…These can be classified based on size (microadenomas when they are smaller than 10 mm and macroadenomas when 10 mm or larger) and secretory pattern (e.g., corticotroph, somatotroph, melanotroph, or plurihormonal) (6). Somatotroph adenomas represent the most common pituitary tumor in cats and, when associated with hypersomatotropism, present with weight gain, broad facial and limb features, abdominal organomegaly, heart murmur, and diabetes mellitus-related clinical signs (7)(8)(9). In a recent study (9), the median survival time in cats with pituitary adenomas varied from 515 to 730 days, depending on the tumor type (9).…”

“…Somatotroph adenomas represent the most common pituitary tumor in cats and, when associated with hypersomatotropism, present with weight gain, broad facial and limb features, abdominal organomegaly, heart murmur, and diabetes mellitus-related clinical signs (7)(8)(9). In a recent study (9), the median survival time in cats with pituitary adenomas varied from 515 to 730 days, depending on the tumor type (9). Diagnosis and treatment normally depend on clinical signs, advanced imaging investigation, histopathology, transsphenoidal surgery, medical management, or radiotherapy (6,10).…”