Histopathologic Findings in Canine Pituitary Glands

Transsphenoidal Surgery for Pituitary Tumors

Transsphenoidal surgery for the treatment of pituitary masses in cats and dogs has become a more established treatment over the last 2 decades. Although expert centers and surgeons that provide this service remain limited, the patient population presented for pituitary surgery increases with wider availability of advanced imaging, together with more challenging cases. In this review, the current state of hypophysectomy is described with future challenges and opportunities.

Cytologic features of canine melanotroph and corticotroph pituitary adenomas

BACKGROUND

The introduction of intraoperative cytology revolutionized neurosurgical procedures in human medicine, providing real-time diagnostic guidance to surgeons and contributing to improved patient outcomes. In the realm of veterinary medicine, the understanding of pituitary tumors in dogs and cats remains limited due to challenges in obtaining antemortem samples of central nervous system lesions.

OBJECTIVES

The aim of this study was to describe the cytologic features of pituitary adenomas in 12 dogs that underwent hypophysectomy.

METHODS

The series included nine melanotroph adenomas and three corticotroph adenomas. Definitive diagnosis was based on histopathology and immunohistochemistry.

RESULTS

Cytologically, the adenomas had high numbers of bare nuclei and intact cells that were round to polygonal and situated individually or in small clusters. The intact cells had round to oval, eccentric nuclei with finely stippled chromatin and one to three prominent nucleoli and ample to abundant lightly basophilic to amphophilic, grainy cytoplasm with distinct borders, and variable numbers of discrete vacuoles. Mild-to-moderate anisocytosis and anisokaryosis, occasional binucleation, rare and atypical mitotic figures, and nuclear molding were also observed.

CONCLUSIONS

The results suggest that intraoperative cytology of canine pituitary adenomas holds promise as a valuable diagnostic tool, aiding swift differentiation from other sellar masses before histologic confirmation. Cytologic characterization of pituitary adenomas in dogs is exceptionally rare in the scientific literature, making this study one of the first to offer a comprehensive description of these cytologic features.

Lymphocytic hypophysitis in dogs infected with Leishmania spp

Background

Morphological involvement of endocrine glands, such as the pituitary gland, remain uninvestigated in dogs with canine visceral leishmaniasis. Therefore, this study investigated the presence of amastigotes of Leishmania spp. and characterized inflammatory changes, highlighting the involvement of TCD3+ lymphocytes in different regions of the pituitary gland of dogs.

Methods

Samples were collected from 21 naturally infected dogs and 5 control, uninfected dogs. The different pituitary regions were analyzed in histological sections stained with hematoxylin and eosin (HE) under light microscopy. Inflammation was classified by intensity in a score from 0 to 3, absent (0), mild (1), moderate (2), and marked (3). The immunohistochemical (IHC) evaluation was performed in five high-power fields (hot spot) in a 40x objective of each region with manual counting (Image J1.52ª) of the TCD3+ lymphocytes and for amastigotes analyzed in 40x and 100x objectives. The Shapiro-Wilk test was used to assess the normality of the data. Differences between groups were determined by the Mann Whitney test. The correlation between variables was assessed by Sperman's correlation test. p < 0.05 were considered statistically significant.

Results

Amastigotes from the pituitary glands of two infected dogs were identified using IHC. The histopathological evaluation stained with hematoxylin and eosin showed greater intensity of inflammation in the pars distalis and pars intermedia regions of infected dogs. IHC for TCD3+ lymphocytes showed a higher median number of immunolabeled cells in pars nervosa in the infected group than in the control group (p < 0.05); and expecting a variation in the distribution and number of these cells in naturally infected dogs, the median of the control group was considered a cut-off point, an increase in T lymphocytes (p < 0.05) was also observed in the pars intermedia and pars distalis of an infected subgroup (n = 10). A moderate significant correlation between the intensity of inflammation and the number of immunolabeled TCD3+ lymphocytes was established in the analyzed pituitary regions, characterizing the occurrence of hypophysitis.

Conclusion

These findings presuppose that inflammation and/or the parasite in the pituitary region can result in gland dysfunction, worsening the clinical condition of the patient and compromising the efficiency of treatment and prognosis.

Effect of pituitary-dependent hypercortisolism on the survival of dogs treated with radiotherapy for pituitary macroadenomas

BACKGROUND

Radiotherapy (RT) is an effective treatment for dogs presented with neurologic signs caused by pituitary tumors. However, its impact on the outcome of concurrent pituitary-dependent hypercortisolism (PDH) is controversial.

OBJECTIVES

Determine whether dogs with PDH have longer survival after pituitary RT compared with dogs with nonhormonally active pituitary masses and to evaluate whether clinical, imaging, and RT variables affect survival.

ANIMALS

Ninety-four dogs divided into 2 groups: PDH and non-PDH, based on the presence of hypercortisolism. Forty-seven dogs were allocated to the PDH group and 47 to the non-PDH group.

METHODS

Retrospective cohort study in which clinical records of dogs undergoing RT for pituitary macroadenomas between 2008 and 2018 at 5 referral centers were retrospectively evaluated.

RESULTS

Survival was not statistically different between PDH and non-PDH groups (median survival time [MST], 590 days; 95% confidence interval [CI], 0-830 days and 738 days; 95% CI, 373-1103 days, respectively; P = .4). A definitive RT protocol was statistically associated with longer survival compared with a palliative protocol (MST 605 vs 262 days, P = .05). The only factor statistically associated with survival from multivariate Cox proportional hazard analysis was total radiation dose (Gy) delivered (P < .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

No statistical difference in survival was identified between the PDH and non-PDH groups, and longer survival was associated with higher Gy delivered.

Clinical characteristics and outcome in 15 dogs treated with transsphenoidal hypophysectomy for nonfunctional sellar masses

OBJECTIVE

To characterize the clinical features, neurological examination findings, diagnostic imaging results, histopathological findings, and outcome following transsphenoidal hypophysectomy (TSH) in dogs with nonfunctional sellar masses (NFSM).

STUDY DESIGN

Multi-institutional retrospective study.

METHODS

Medical records of dogs that underwent TSH for a NFSM were reviewed for clinical signs, physical and neurological examination findings, diagnostic imaging results, endocrine testing, surgery reports, and outcome. Magnetic resonance (MR) imaging was rereviewed, and tumors were classified using the previously described system according to pituitary tumor extension and vascular involvement. Owners of dogs that survived to discharge were contacted.

RESULTS

The majority of dogs presented for mentation change (12/15). The mean pituitary to brain ratio (P/B ratio) was 1.05 (0.6-1.4). Eight dogs had a tumor imaging classification of 5B. Eleven dogs were diagnosed with a nonfunctional pituitary adenoma (NFPA). Perioperative mortality was 33% (5/15). The median survival for all dogs was 232 days (0-1658). When dogs that did not survive to discharge were excluded, the median survival time was 708 days. Seven of 10 dogs that survived the perioperative period received adjunctive therapy. Owner assessment of outcome was excellent (6/7) to good (1/7).

CONCLUSION

The common presenting complaint for dogs with large NFSM causing mass effect was mentation changes. Dogs with NFPA that survived to discharge and received adjunctive therapy had good to excellent outcomes.

CLINICAL SIGNIFICANCE

Transsphenoidal debulking with adjunctive therapy can be considered for the treatment of NFSM causing clinical signs of mass effect in dogs. Successful long-term outcomes are possible.

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

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.

Pituitary tumour types in dogs and cats

Pituitary tumours are common in dogs and are being increasingly recognized in cats. Pituitary tumours are usually classified as adenomas and should only be classified as carcinomas when there is evidence of metastatic spread of the tumour, which is rare. Despite the benign nature of most pituitary tumours, they can still compress or invade neighbouring tissues. Pituitary tumours can be functional (hormonally active) or non-functional (hormonally silent). The aim of this review was to provide an overview of the different pituitary tumour types in dogs and cats that have been reported in the literature. In dogs, the most common pituitary tumour type is the corticotroph adenoma, which can cause pituitary-dependent hypercortisolism. In cats, the most common pituitary tumour is the somatotroph adenoma, which can cause hypersomatotropism, and the second-most common is the corticotroph adenoma. A lactotroph adenoma has been described in one dog, while gonadotroph, thyrotroph and null cell adenomas have not been described in dogs or cats. Hormonally silent adenomas are likely underdiagnosed because they do not result in an endocrine syndrome. Tools used to classify pituitary tumours in humans, particularly immunohistochemistry for lineage-specific transcription factors, are likely to be useful to classify canine and feline pituitary tumours of unknown origin. Future studies are required to better understand the full range of pituitary adenoma pathology in dogs and cats and to determine whether certain adenoma subtypes behave more aggressively than others. Currently, the mechanisms that underlie pituitary tumorigenesis in dogs and cats are still largely unknown. A better understanding of the molecular background of these tumours could help to identify improved pituitary-targeted therapeutics.

Pituitary Surgery: Changing the Paradigm in Veterinary Medicine in the United States

Medical management is currently the most common treatment for pituitary-dependent hyperadrenocorticism and hypersomatotropism/acromegaly in veterinary medicine. Medical management does not provide a cure for either disease process, and rarely is pituitary imaging a part of initial diagnostics. Early pituitary imaging in animals with clinically functional pituitary tumors provides a baseline assessment, allows monitoring of tumor changes, and permits radiation and surgical planning. Surgery is the only treatment for pituitary tumors that has curative intent and allows for a definitive diagnosis. Surgical removal of pituitary tumors via transsphenoidal hypophysectomy is an effective treatment for clinical pituitary tumors in patients exhibiting endocrine abnormalities associated with pituitary-dependent hyperadrenocorticism and hypersomatotropism. Surgery, however, is rarely pursued until patients have failed medical management, and often not until they are showing neurologic signs, making surgical success challenging. It is well documented that dogs surgically treated when the pituitary mass is small have a lower mortality, a lower recurrence rate, and a longer survival than those with larger pituitary masses. Providing owners with the option of early pituitary imaging in addition to medical, surgical, and radiation treatment options should be the standard of care for animals diagnosed with pituitary-dependent hyperadrenocorticism or hypersomatotropism.

Xanthogranulomatous Pituitary Adenoma in a Dog with Typical Hyperadrenocorticism

Xanthogranuloma of the sellar region has been reported in both humans and animals. The lesion is rare, and its aetiology and pathogenesis are not fully understood. The association of sellar xanthogranuloma with an adenoma, known as xanthogranulomatous pituitary adenoma (XPA), is an extremely rare condition in humans and is usually associated with anterior pituitary insufficiencies, headache, vomiting and visual deficits. We present the first report of XPA in an animal. A 7-year-old male neutered Labrador Retriever was presented for investigation of progressive lethargy, vomiting and hyporexia, having been previously diagnosed with chronic kidney disease, pituitary-dependent hyperadrenocorticism and hypoparathyroidism. The dog was euthanized due to lack of response to medical treatment and post-mortem examination revealed XPA. Although rare, xanthogranulomatous lesions should be considered in patients with pituitary disease.

Presence of CD3+ and CD79a+ Lymphocytes in the Pituitary Gland of Dogs at Post-mortem Examination

Hypophysitis has been reported occasionally in dogs, with most cases resembling primary lymphocytic hypophysitis in man. Although it is generally assumed that lymphocytes are not present normally in the canine pituitary gland, few studies have investigated this hypothesis. However, lymphocytes are recognized in the pituitary gland of people and horses without signs of pituitary disease. It is unknown to what degree lymphocyte infiltration of the pituitary gland might occur as an incidental finding in dogs. The aim of the present study was to investigate the presence and distribution of lymphocytes in the pituitary gland of dogs without clinical suspicion of pituitary disease. Twenty dogs were subjected to routine necropsy examination. Formalin-fixed and paraffin wax-embedded sections of pituitary were stained with haematoxylin and eosin (HE) or subjected to immunohistochemistry (IHC) using primary antibodies specific for the T-cell marker CD3 and the B-cell marker CD79a. The number of CD3⁺ and CD79a⁺ cells per area unit (CPA) was determined for different pituitary regions. Two dogs had extensive neoplastic lesions in the pituitary gland and were excluded from analysis. In the remaining 18 dogs, occasional scattered CD3⁺ cells were found in the pituitary gland. There was a significant difference in CD3⁺ CPA between pituitary regions (P = 0.001). The highest CD3⁺ CPA was found in the pars tuberalis (median 41.3 cells/mm², interquartile range 20.9-50.5 cells/mm²). In six of the 18 dogs (33%), CD79a⁺ cells were detected in small number (median total cell number 0 cells/section, interquartile range 0-1.0 cells/section). This study shows that T cell, and fewer B cells, may be found in the pituitary gland of dogs without clinical suspicion of pituitary disease. Regional difference in T-cell density, with the highest CD3⁺ CPA in the pars tuberalis, may imply regional immunoregulatory functions in the canine pituitary gland.

A Recurrent Suprapituitary Ependymal Cyst Managed by Endoscopy-Assisted Transsphenoidal Surgery in a Canine: A Case Report

A 9-years-old spayed female mixed-breed dog was referred for the evaluation of intermittent head tremors, obtundation, long-standing blindness, and a tendency to seek confined spaces. The dog lost its vision 6 months before the current presentation. A menace response was absent on ophthalmological examination. Neurological examination did not show any abnormalities. A cyst measuring 16 × 18 × 14 mm was observed above the pituitary gland on magnetic resonance imaging. It extended toward the frontal area and compressed the optic chiasm and hypothalamic regions. A minimum preoperative database, including the findings of other required blood tests, was prepared. No abnormal laboratory findings were observed. Endoscopy-assisted transsphenoidal hypophysectomy was performed to remove the pituitary gland, drain the cyst, and partially excise the cyst wall. Normal pituitary gland tissue was observed on histopathology, and the mass was found to have a neuroendocrine or ependymal origin on cytology. Strict post-operative laboratory tests were performed at 1-h intervals for 24 h. An empty sella turcica region, and a collapsed and empty cyst wall was observed on follow-up magnetic resonance imaging. After 3 days of observation, the dog was discharged with a prescription of substitution therapy. However, the dog presented with the same signs and symptoms 73 days after the surgery. Cyst recurrence was apparent on magnetic resonance imaging. The owner requested euthanasia, and an ependymal cyst was observed on necropsy. To the best of our knowledge, we present the first case of an intra- and suprasellar ependymal cyst, and its surgical management in a canine. The findings from this case suggest that endoscopic transsphenoidal drainage and hypophysectomy could be a good surgical approach in cases where involvement of the pituitary gland is confirmed or strongly suspected on the basis of cytological and imaging findings.

Immunohistochemical Evaluation of Canine Pituitary Adenomas Obtained by Transsphenoidal Hypophysectomy

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.