Immunohistochemical Evaluation of Canine Pituitary Adenomas Obtained by Transsphenoidal Hypophysectomy

Abstract

Hypophysectomy specimens from 16 dogs with pituitary adenoma were evaluated with periodic acid-Schiff (PAS), reticulin, and immunohistochemistry for adrenocorticotrophic hormone (ACTH), melanocyte stimulating hormone (MSH), growth hormone (GH), and Ki-67. The reticulin network was obliterated in all adenomas. One adenoma expressed ACTH and GH. Eight corticotroph adenomas were basophilic to chromophobic, and PAS- and ACTH-positive. Seven melanotroph adenomas were distinguished from corticotroph adenomas by expression of MSH. Pituitary-dependent hypercortisolism was diagnosed in 5 of 8 dogs with corticotroph and 4 of 7 with melanotroph adenoma. Pituitary height/brain area (P/B) ratio was elevated in all dogs. Previous canine hypophysectomy studies suggested that melanotroph adenomas were larger and carried a worse prognosis than corticotroph adenomas; however, in this study, corticotroph adenomas in comparison to melanotroph adenomas were larger (median P/B ratio: 1.06 versus 0.76), more proliferative (median Ki-67 index: 9.47% versus 1.99%), and associated with shorter survival (median: 300 versus 793 days). Recommended immunohistochemistry for PAS-positive pituitary adenomas includes ACTH and MSH to distinguish corticotrophs from melanotrophs and Ki-67 for proliferation index.

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

“…46 Corticotroph adenomas, which express ACTH but not MSH, are also common in dogs. 27 However, all ACTH-expressing adenomas in this feline study also expressed MSH, so were classified as melanotroph adenoma. Because IHC for MSH is not routine in all veterinary diagnostic laboratories, feline melanotroph adenomas may have been underdiagnosed or misclassified as corticotroph adenomas based on their ACTH expression.…”

“…Because IHC for MSH is not routine in all veterinary diagnostic laboratories, feline melanotroph adenomas may have been underdiagnosed or misclassified as corticotroph adenomas based on their ACTH expression. As in the dog, 27 hypercortisolism was diagnosed in about half the cats with a melanotroph adenoma.…”

<p>Transsphenoidal Surgery in Canines: Safety, Efficacy and Patient Selection</p>

“…33,41 Regarding the relationship between pituitary tumor origin and size, some reports have indicated that adenomas originating from the intermediate lobe were larger than those originating from the anterior pituitary; 23 conversely, other reports have shown that adenomas originating from the anterior pituitary grow larger than those originating from the intermediate lobe. 3,47 However, currently, no indicators have been identified for predicting the adenoma growth rate after the diagnosis of pituitary tumors in canines. Reports have analyzed the Ki-67 and minichromosome maintenance-7 (MCM7) expression levels in sampled pituitary tumors, and suggested that in canine pituitary adenomas, MCM7 level may be a more effective growth marker than Ki-67 level.…”

“…Reports have analyzed the Ki-67 and minichromosome maintenance-7 (MCM7) expression levels in sampled pituitary tumors, and suggested that in canine pituitary adenomas, MCM7 level may be a more effective growth marker than Ki-67 level. 47,48 However, a clinical indicator that can predict adenoma growth rate prior to surgery is still needed. to cases without involvement of the cavernous sinus and/or arterial circle of Willis, and type B referring to cases with involvement of either or both.…”

“…Regarding the growth markers of the pituitary adenoma itself, the survival time is short when the Ki-67 index is >3%. 47 In addition, Vastenhout et al reported recently that the pituitary tumor-transforming gene 1 (PTTG1) mRNA expression level was three times higher than normal in an ACTH-producing pituitary tumor and that tumors with higher PTTG expression levels had shorter remission durations after TSS. 60…”