Transsphenoidal hypophysectomy in beagle dogs: evaluation of a microsurgical technique

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.

Transsphenoidal hypophysectomy for the treatment of hypersomatotropism secondary to a pituitary somatotroph adenoma in a dog

Pituitary-dependent hypersomatotropism is rarely diagnosed in dogs and surgical treatment is not reported. A 6-year-10-month male neutered Patterdale Terrier presented with polyuria, polydipsia, progressive pharyngeal stertor, excessive hair growth and widened facial features and paws. Serum insulin-like growth factor-1 concentration via radioimmunoassay was consistent with hypersomatotropism (1783 ng/mL). A pituitary mass was identified on magnetic resonance and computed tomography imaging. Six weeks later, glucosuria, starved hyperglycemia and serum fructosamine above the reference range (467.6 μmol/L, RI 177-314) were documented, consistent with diabetes mellitus. Transsphenoidal hypophysectomy was performed under general anesthesia without complications. Pituitary histopathology identified an acidophil neoplasm, with positive immunostaining for growth hormone. Postoperatively, there was rapid resolution of clinical, biochemical and morphologic changes of hypersomatotropism with persistence of diabetes mellitus. This case demonstrates successful resolution of hypersomatotropism with ongoing diabetes mellitus in a dog after surgical treatment by transsphenoidal hypophysectomy.

Challenges of transsphenoidal pituitary surgery in severe brachycephalic dogs

Introduction

Transsphenoidal hypophysectomy is the standard surgical technique for the excision of pituitary neoplasms. Anatomy may be more obscured in brachycephalic skull types due to the crowding of soft tissue and osseous structures. We describe the unique challenges to approach the sphenoid bone and localize the correct burr hole site in severe brachycephalic dogs.

Materials and methods

A single institution retrospective case series of brachycephalic dogs with pituitary-dependent hypercortisolism (PDH). Preoperative computed tomography enabled 3D-, and cross-sectional reconstruction to plan and dry-practice the position of the ideal burr hole in relation to the sella turcica, pterygoid hamular processes, and hard palate. Rostral burring of the caudal hard palate obscuring the direct sphenoid approach necessitated adaptations to the original transsphenoidal hypophysectomy procedure. Postoperative outcomes and complications with respect to those seen in mesocephalic dogs are described.

Results

Ten brachycephalic dogs including French Bulldogs (n = 9) and a single Dogue de Bordeaux were included. All dogs were diagnosed with PDH and had preoperative advanced imaging performed on the skull. All but one dog had an enlarged pituitary gland, with a median pituitary/brain value of 0.5 (range 0.21-0.9). A total of 11 transsphenoidal hypophysectomy procedures were performed in these 10 dogs. Rostral extension of the soft palate incision into the hard palate was performed to access the burr hole site on the sphenoid bone. Major complications included aspiration pneumonia (n = 1), severe gastroesophageal reflux (n = 1), and central nervous signs (=1). All dogs survived until discharge, with a median time to follow-up of 618 days (range 79-1,669 days). Seven dogs experienced long-term remission of PDH.

Conclusion

Brachycephalic dogs undergoing transsphenoid al hypophysectomy benefit from meticulous presurgical planning and extension of the approach into the caudal hard palate. Advanced surgical skills can render a good outcome in a technically challenging environment.

Regression of venous thrombus after trans-sphenoidal hypophysectomy for pituitary-dependent hyperadrenocorticism in a dog

An 8.0-kg 8-year-old male dachshund was presented for surgical treatment of suspected pituitary-dependent hyperadrenocorticism with portal vein thrombosis. Advanced diagnostic imaging revealed a thrombus in the splenic and portal veins. For the portal vein thrombus, CT angiography showed an enhanced timing delay in the lateral right and caudate liver lobes. Blood tests showed a marked increase in the liver panel, including total bile acid. Brain MRI revealed a pituitary mass, suggesting pituitary-dependent hyperadrenocorticism. The mass was completely resected. The preoperative antithrombotic therapy of rivaroxaban (0.66 mg/kg, PO, once per day) and clopidogrel sulphate (1.66 mg/kg, PO, once per day) was continued postoperatively. Six months after resection of the pituitary mass, the thrombus had disappeared. Further studies are required to prove a causal association between the disappearance of the thrombus and the treatments provided.

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.

Adrenocorticotropic hormone-producing pituitary adenoma with pituitary apoplexy treated by surgical decompression: a case report

Background

Pituitary-dependent hypercortisolism (PDH) is one of the most common endocrine disorders in veterinary medicine. However, there are few reports on pituitary tumor apoplexy (PTA) in dogs and no reports on its surgical intervention in veterinary medicine. Accordingly, the appropriate treatment is unknown. Herein, a case of PDH and PTA in a dog treated surgically is described.

Case presentation

A mongrel female dog (spayed; age, 8 years and 8 months; weight, 6.1 kg) with persistently elevated alkaline phosphatase underwent adrenocorticotropic hormone (ACTH) stimulation testing (post-stimulation cortisol: 20.5 μg/dL), abdominal ultrasonography (adrenal gland thickness: left, 5.7 mm; right, 8.1 mm), and brain magnetic resonance imaging (MRI) (pituitary-to-brain ratio [PBR], 0.61) at the referral hospital, resulting in a diagnosis of PDH (day 0). On day 9, the dog visited XXXX for the preparation of pituitary surgery to treat PDH. However, on days 10–15, the dog developed a loss of energy and appetite, bloody diarrhea, vomiting, and a decreased level of consciousness. However, on day 16, the dog’s condition recovered. A preoperative MRI scan performed on day 52 (the day of surgery) showed apoplexy in the dorsal pituitary region (PBR, 0.68). Based on the PTA findings, the risks of surgery were described to the owner, and approval was obtained. At the time of trans-sphenoidal surgery, a partial pituitary resection was performed with preservation of the PTA area due to adhesions between the PTA area of the right side of the pituitary and surrounding tissues. The resected pituitary tissue was diagnosed as an ACTH-producing adenoma, with necrotic and hemorrhagic findings. As of day 290, endogenous ACTH and cortisol levels did not exceed the reference range.

Conclusions

The acute signs that occurred on days 10–15 were most likely caused by PTA. Therefore, when signs similar to those detected in acute hypoadrenocorticism are observed in dogs with PDH, it is necessary to include PTA as a differential diagnosis. Trans-sphenoidal surgery may be effective in PDH-affected dogs that develop PTA, but careful attention should be paid to tissue adhesions secondary to hemorrhage that may occur after PTA.

A 3-Dimensional Printed Patient-Specific Surgical Guide to Facilitate Transsphenoidal Hypophysectomy in Dogs

Objective

Hypophysectomy in dogs is a difficult surgery that requires specific learning and training. We aimed to evaluate the accuracy of a 3-dimensional printed patient-specific surgical guide to facilitate choosing the entry point in the basisphenoid bone before approaching the sella turcica during transsphenoidal hypophysectomy in dogs.

Methods

Two canine cadavers and 8 dogs undergoing transsphenoidal hypophysectomy for Cushing's disease treatment, involving design and fabrication of a 3-dimensional printed guide. The ideal entry point in the basisphenoid bone outer cortical layer was determined in each dog pre-operatively; its anatomical location was described with a set of measurements then compared to post-operative computed tomography measures describing the location of the outer cortical window created in the basisphenoid bone.

Results

Several guide designs were proposed, and a consensus reached based on surgeons' experience performing hypophysectomy. The device chosen could be applied to the size and shape of skulls encountered in this case series. The pre-planned measurements were comparable to post-operative measurement (there was also no statistical difference), with median of differences <0.1 mm, which we judged as clinically acceptable.

Clinical Significance

Hypophysectomy in dogs is a challenging procedure that has a learning curve and needs to be performed by specialist neurosurgeons. We propose that a low-profile 3-dimensional printed surgical guide can aid the specialist neurosurgeon to locate the burring site of the outer cortical layer of the basisphenoid bone at a pre-defined location and with good accuracy. It does not alleviate the need to understand the anatomy of the region and to know how to create a slot within the basisphenoid bone, which remains essential to enter the sella turcica. This device could help specialist veterinary neurosurgeons wishing to be trained to perform hypophysectomy.

Transoral ventral tympanic bulla osteotomy in cats: 13 cases (2016-2019)

OBJECTIVE

To analyze the results of transoral ventral bulla osteotomy (TOVBO) in cats.

ANIMALS

13 client-owned cats treated by TOVBO between February 2016 and February 2019.

PROCEDURES

Medical records of cats with a diagnosis of middle ear disease (MED) that underwent TOVBO were reviewed. The procedure was similar to the one described for dogs. Short-term follow-up was obtained via clinical examination before discharge and at day 15 postoperatively. Long-term follow-up was performed via telephone interview.

RESULTS

13 cats (age range, 8 months to 12 years) underwent unilateral (n = 10) or bilateral (3) TOVBO (16) for the treatment of tympanic bulla (TB) infection (10), nasopharyngeal inflammatory polyps (5), or bullet retrieval from the TB (1). There were no intraoperative complications. One cat with a poor preoperative status died at postoperative day 3 from pneumonia. Eight cats experienced postoperative complications including head tilt (n = 2), Horner syndrome (3), loss of appetite (2), and temporary blindness (1). Collected samples confirmed the presence of nasopharyngeal inflammatory polyps (5), or otitis media (8). Six months after surgical intervention, 9 cats were free of MED signs.

CLINICAL RELEVANCE

This oral approach provided a good access to the TB in all cases. The complications observed after TOVBO were similar to those for VBO. In cats, TOVBO seems to be an acceptable and safe minimally invasive alternative to the other approaches of the TB to address MED.

Three Cases of Transtracheal Catheter Oxygenation for Postoperative Dyspnoea with Pituitary-Dependent Hyperadrenocorticism in Dogs Treated by Surgery

Transsphenoidal surgery (TSS) is a curative treatment for pituitary-dependent hyperadrenocorticism, and its use in dogs has recently increased. One of the most serious postoperative complications of TSS is dyspnoea. We report three cases where transtracheal catheter oxygen therapy prevented death from respiratory distress secondary to enlarged soft palate after TSS.

Evaluation of the accuracy of three-dimensionally printed patient-specific guides for transsphenoidal hypophysectomy in small-breed dogs

OBJECTIVE

To assess the accuracy of transsphenoidal hypophysectomy using 3-D printed patient-specific guides (3D-PSGs) in small-breed dogs.

ANIMALS

Heads obtained from the cadavers of 19 small-breed dogs (ex vivo portion of study) and 3 healthy adult (3 to 4 years) purpose-bred Beagles with a median body weight of 9.2 kg.

PROCEDURES

In the ex vivo study, CT images of the cadavers were collected. The position, width, and length of the pituitary fossa and the pilot hole (insertion angle and place) were measured. Using PSGs, 19 pilot holes were made for the pituitary gland fossa, and CT was performed to assess the position accuracy. In the in vivo study, 3 surgical windows from the pilot holes were made using PSGs. Repeated CT and MRI were performed to evaluate the safeness and effectiveness of PSGs, followed by necropsy.

RESULTS

In the ex vivo study, the median (interquartile range) difference between the pre- and postoperative insertion angles was 2° (0° to 3.5°) and the median deviation of the pilot hole was 0.46 mm (0 to 1.58 mm). In the in vivo study, the surrounding structures were not damaged, and favorable outcomes were evident in terms of the shape, size, and position of the surgical window.

CLINICAL RELEVANCE

3D-PSGs provided a safe and effective surgical window for transsphenoidal hypophysectomy. Our findings emphasized the applicability of PSGs in brain surgery, in terms of accuracy and effectiveness.

Plasma sodium and potassium concentrations after hypophysectomy in dogs with corticotroph adenomas

Background

Electrolyte abnormalities, especially hypernatremia, are frequent complications after transsphenoidal hypophysectomy in dogs with pituitary‐dependent hypercortisolism.

Objectives

To describe electrolyte abnormalities after transsphenoidal hypophysectomy and to investigate possible associations between postoperative hypernatremia and clinical and surgical variables as well as with postoperative outcome.

Animals

One hundred and twenty‐seven client‐owned dogs.

Methods

Dogs with pituitary corticotroph adenomas that underwent transsphenoidal hypophysectomy were retrospectively included. Plasma sodium and potassium concentrations were measured −2, +2, +8, +24, and +48 hours from hypophysectomy. Clinical (breed, age, body weight, skull type, urinary cortisol/creatinine ratio, percentage of suppression to dexamethasone) and surgical variables (duration of anesthesia and surgery, pituitary dimensions) were compared to the development of hypernatremia.

Results

Postoperative hypernatremia developed in 46.5% (57/127) of dogs and hyponatremia in 6.3% (8/127). Plasma sodium concentration increased after surgery and peaked at 8 hours after surgery, normalizing after 24 to 48 hours. Plasma potassium concentration increased without exceeding the reference limit.

No significant associations were found between clinical and surgical variables and hypernatremia, or between hypernatremia and postoperative death, long‐term survival or recurrence.

Surgery time was significantly longer in dogs that developed persistent diabetes insipidus (P = .02) and persistent diabetes insipidus occurred more frequently in dogs with enlarged pituitary glands (P = .01).

Conclusion and Clinical Importance

Hypernatremia remains a frequent postoperative complication after transsphenoidal hypophysectomy but did not appear to have an impact on postoperative outcome. No predisposing factor to postoperative hypernatremia was identified. Variations in plasma potassium concentrations do not seem to influence postoperative outcome.

Case Report: Radioactive Holmium-166 Microspheres for the Intratumoral Treatment of a Canine Pituitary Tumor

Introduction: In this case study, a client-owned dog with a large pituitary tumor was experimentally treated by intratumoral injection of radioactive holmium-166 microspheres (166HoMS), named 166Ho microbrachytherapy. To our knowledge, this is the first intracranial intratumoral treatment through needle injection of radioactive microspheres. Materials and Methods: A 10-year-old Jack Russell Terrier was referred to the Clinic for Companion Animal Health (Faculty of Veterinary Medicine, Utrecht University, The Netherlands) with behavioral changes, restlessness, stiff gait, and compulsive circling. MRI and CT showed a pituitary tumor with basisphenoid bone invasion and marked mass effect. The tumor measured 8.8 cm3 with a pituitary height-to-brain area (P/B) ratio of 1.86 cm-1 [pituitary height (cm) ×10/brain area (cm2)]. To reduce tumor volume and neurological signs, 166HoMS were administered in the tumor center by transsphenoidal CT-guided needle injections. Results: Two manual CT-guided injections were performed containing 0.6 ml of 166HoMS suspension in total. A total of 1097 MBq was delivered, resulting in a calculated average tumor dose of 1866 Gy. At 138 days after treatment, the tumor volume measured 5.3 cm3 with a P/B ratio of 1.41 cm-1, revealing a total tumor volume reduction of 40%. Debulking surgery was performed five months after 166HoMS treatment due to recurrent neurological signs. The patient was euthanized two weeks later at request of the owners. Histopathological analysis indicated a pituitary adenoma at time of treatment, with more malignant characteristics during debulking surgery. Conclusion: The 40% tumor volume reduction without evident severe periprocedural side effects demonstrated the feasibility of intracranial intratumoral 166HoMS treatment in this single dog.

Transsphenoidal Surgery in Canines: Safety, Efficacy and Patient Selection

Pituitary-dependent hyperadrenocorticism (PDH) is the cause of approximately 80-85% of naturally occurring cases of hyperadrenocorticism(HAC) in canines and is triggered by an adrenocorticotropic hormone (ACTH)-producing pituitary adenoma or hyperplasia of the corticotroph in the pituitary anterior lobe or intermediate lobe. Transsphenoidal surgery(TSS) is an effective treatment that can directly remove pituitary tumors that cause PDH in canines under a single course of general anesthesia. However, careful evaluations of the definitive diagnosis, adenoma size and growth rate, relationship with surrounding tissue, general condition, and neurosurgical procedural skill involved in each case are important to determine TSS suitability. The basic principle is to confirm that the present HAC case is PDH, that is, an ACTH-producing adenoma or the hyperplasia of the corticotroph originating from either the pituitary anterior or intermediate lobe. Evaluations based on endocrinology, particularly plasma ACTH concentration, and imaging diagnosis, particularly MRI is essential for definitive diagnosis. Enlarged pituitary tumors can shorten the post-TSS survival time, increase the recurrence rate of clinical symptoms, and increase the risk for developing permanent central diabetes insipidus. Therefore, complete removal of adenomas of up to Grade IIIA according to the MRI-based classification system is relatively easy to achieve with TSS, and long-term remission and survival can be expected.

Virus Injection to the Pituitary via Transsphenoidal Approach and the Innervation of Anterior and Posterior Pituitary of Rat

The theory holds that the anterior pituitary in mammals receives humoral regulation. Previous studies have reported that the pars distalis of the anterior pituitary of several mammalian species contains substance P-, calcitonin gene-related peptide (CGRP)-, and galanin-like immunoreactive nerve fibers, but the origins of these nerve fibers are unclear. Removal of the pituitary gland, also called hypophysectomy, involves methods that access the pituitary gland via the transauricular or parapharyngeal pathways. However, these methods are not applicable for viral tracer injection to investigate the innervation of the anterior pituitary. The transauricular technique leads to inaccuracies in locating the pituitary gland, while the parapharyngeal approach causes high mortality in animals. Here, we introduce a protocol that accesses the pituitary gland in the rat via the transsphenoidal pathway. This method imitates surgical manipulations such as endotracheal intubation and sphenoid bone drilling, which involve the use of custom-made devices. Using the transsphenoidal pathway greatly improves the survival rate of rats because no additional dissection of blood vessels and nerves is required. Moreover, the pituitary gland can be viewed clearly and directly during the operation, making it possible to accurately inject pseudorabies virus (PRV) 152-expressing enhanced green fluorescent protein (EGFP) into the anterior or posterior pituitary, respectively. After injecting PRV 152 into the anterior pituitary, we found no evidence of direct innervation of the anterior pituitary in the rat brain. However, PRV 152 injection into the posterior pituitary revealed retrograde transneuronal cell bodies in many brain areas, including the CA1 field of the hippocampus, the basolateral amygdaloid nucleus, posterior part (BLP), the arcuate hypothalamic nucleus (Arc), the dorsal portion of the dorsomedial hypothalamic nucleus (DMD), the suprachiasmatic nucleus (SCh), and the subfornical organ (SFO). In the present study, we provide a description of a possible model of hypophysectomy or pituitary injection, and identify brain regions involved in regulating the rat pituitary gland using transneuronal retrograde cell body labeling with PRV.

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.

Transsphenoidal surgery: accuracy of an image-guided neuronavigation system to approach the pituitary fossa (sella turcica)

OBJECTIVE

To determine the accuracy of locating the pituitary fossa with the Brainsight neuronavigation system by determining the mean target error of the rostral (tuberculum sellae) and caudal (dorsum sellae) margins of the pituitary fossa.

STUDY DESIGN

Experimental cadaveric study.

ANIMALS

Ten canine cadavers.

METHODS

Computed tomography (CT) and MRI were performed on each cadaver with fiducials in place. Images were saved to the neuronavigation computer and used to plan the drilling approach. The cadavers were placed in the surgical head clamp of the Brainsight system and positioned for a transsphenoidal approach. On the basis of the planning, 2 localization points were drilled, 1 each at the rostral and caudal margins of the pituitary fossa, and CT was repeated. Error was assessed from the difference in millimeters between the targets identified during Brainsight planning and the actual location of the 2 points drilled on each cadaver skull as identified by postdrilling CT.

RESULTS

The rostral and caudal margins of the pituitary fossa provided 2 target points per cadaver. The median target error (interquartile range) for all target sites (n = 20) was 3.533 mm (range, 2.013-4.745).

CONCLUSION

This stereotactic system allowed the surgeon to locate the rostral and caudal margins of the pituitary fossa with clinically acceptable accuracy and confidence.

CLINICAL SIGNIFICANCE

Using the Brainsight neuronavigation system for localization during transsphenoidal hypophysectomy may decrease morbidity and surgical time.

Protein expression of somatostatin receptor 2, somatostatin receptor 5 and dopamine D2 receptor in normal pituitary gland and ACTH-secreting pituitary adenoma in dogs

PURPOSE

To evaluate the protein expression of somatostatin receptor (SSTR) 2, SSTR5 and dopamine D2 receptor (DA2R)-targets of somatostatin analogs and dopamine agonists-in normal canine pituitary and canine adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas.

METHODS

Six normal canine pituitary glands and 14 canine ACTH-secreting pituitary adenoma cases were included in this study. The protein expression of SSTR2, SSTR5 and DA2R was determined by double-label immunofluorescence staining of these receptors and ACTH.

RESULTS

SSTR2, SSTR5, and DA2R proteins were expressed in the anterior and intermediate lobes of normal canine pituitary glands. In the anterior pituitary lobes, the percentages of SSTR2-, SSTR5-, and DA2R-positive cells among the ACTH-positive population were 27.0 ± 8.6%, 27.9 ± 5.9%, and 34.0 ± 9.4%, respectively. In contrast, the corresponding percentages in the intermediate pituitary lobes were 97.8 ± 1.5%, 94.1 ± 4.4%, and 96.1 ± 6.6%, respectively. Of the 14 ACTH-secreting pituitary adenoma cases, 11, 12, and 6 cases expressed SSTR2, SSTR5, and DA2R, respectively. Additionally, four cases showed strong positive staining for both SSTR2 and SSTR5. Two of these were ACTH-secreting pituitary adenomas likely derived from the intermediate pituitary lobe, because these are α-Melanocyte-stimulation hormone (α-MSH)-positive stains.

CONCLUSION

Immunohistological detection and characterization of SSTR2, SSTR5 and DA2R may provide useful additional information for determining treatment options when an ACTH-secreting pituitary adenoma cannot be completely resected, or in the case of recurrence.

Histopathologic Findings in Canine Pituitary Glands

To optimize the histologic evaluation of hypophysectomy specimens, sections of 207 canine pituitary glands (196 postmortem, 11 hypophysectomy specimens) were reviewed. Adenohypophyseal proliferation was the most common (n = 79) lesion. Proliferative lesions were sparsely to densely granulated; the granules were usually basophilic to chromophobic and periodic acid-Schiff-positive. Adenohypophyseal proliferation was classified as hyperplasia (n = 40) if ≤2 mm diameter with intact reticulin network, as microadenoma (n = 22) for 1–5 mm homogeneous nodules with lost reticulin network, or as macroadenoma (n = 17) for larger tumors. Craniopharyngeal duct cysts were common incidental lesions and the only lesion in 15 dogs. Uncommon diagnoses included lymphoma (n = 4), hemorrhagic necrosis (n = 4), metastatic carcinoma (n = 3), hypophysitis (n = 3), ependymoma (n = 2), craniopharyngioma (n = 2), and 1 case each of metastatic melanoma, pituicytoma, gliomatosis, germ cell tumor, meningioma, and atrophy. The pituitary histologic diagnosis was associated with hyperadrenocorticism (HAC; P < .001) and adrenocortical histologic diagnosis ( P = .025). Both HAC and adrenocortical hyperplasia showed a positive trend with the degree of adenohypophyseal proliferation. The association of adrenocortical hyperplasia with HAC was not significant ( P = .077). Dogs with adenohypophyseal proliferations were older than dogs with normal pituitary glands ( P < .05). Brachycephalic breeds were overrepresented among dogs with pituitary macroadenoma or craniopharyngeal duct cysts, but the association was not statistically significant ( P = .076). Adenohypophyseal hyperplasia was more common than adenoma among postmortem specimens, but was unexpected in >80% of cases. Pituitary macroadenoma was the most common diagnosis in hypophysectomy specimens.

Transsphenoidal Surgery for Pituitary Tumors and Other Sellar Masses

Transsphenoidal surgery is an option for dogs and cats with functional and nonfunctional pituitary masses or other sellar and parasellar masses. An adrenocorticotropic hormone-secreting tumor causing Cushing disease is the most common clinically relevant pituitary tumor in dogs, and the most common pituitary tumor seen in cats is a growth hormone-secreting tumor causing acromegaly. Transsphenoidal surgery can lead to rapid resolution of clinical signs and provide a cure for these patients. Because of the risks associated with this surgery, it should only be attempted by a cohesive pituitary surgery group with a sophisticated medical and surgical team.

Bone morphogenetic protein 4 and bone morphogenetic protein receptor expression in the pituitary gland of adult dogs in healthy condition and with ACTH-secreting pituitary adenoma

The purpose of this study was to investigate the expression of bone morphogenetic protein 4 (BMP4) and its receptors, bone morphogenetic protein receptor I (BMPRI) and BMPRII, in the pituitary gland of healthy adult dogs and in those with ACTH-secreting pituitary adenoma. Quantitative polymerase chain reaction analysis showed that the BMP4 messenger RNA expression level in the ACTH-secreting pituitary adenoma samples was significantly lower than that in the normal pituitary gland samples (P = 0.03). However, there were no statistically significant differences between samples with respect to the messenger RNA expression levels of the receptors BMPRIA, BMPRIB, and BMPRII. Double-immunofluorescence analysis of the normal canine pituitary showed that BMP4 was localized in the thyrotroph (51.3 ± 7.3%) and not the corticotroph cells. By contrast, BMPRII was widely expressed in the thyrotroph (19.9 ± 5.2%) and somatotroph cells (94.7 ± 3.6%) but not in the corticotroph cells (P < 0.001, thyrotroph cells vs somatotroph cells). Similarly, in ACTH-secreting pituitary adenoma, BMP4 and BMPRII were not expressed in the corticotroph cells. Moreover, the percentage of BMP4-positive cells was also significantly reduced in the thyrotroph cells of the surrounding normal pituitary tissue obtained from the resected ACTH-secreting pituitary adenoma (8.3 ± 7.9%) compared with that in normal canine pituitary (P < 0.001). BMP4 has been reported to be expressed in corticotroph cells in the human pituitary gland. Therefore, the results of this study reveal a difference in the cellular pattern of BMP4-positive staining in the pituitary gland between humans and dogs and further revealed the pattern of BMPRII-positive staining in the dog pituitary gland. These species-specific differences regarding BMP4 should be considered when using dogs as an animal model for Cushing's disease.

Lack of Ubiquitin Specific Protease 8 (USP8) Mutations in Canine Corticotroph Pituitary Adenomas

Purpose

Cushing’s disease (CD), also known as pituitary-dependent hyperadrenocorticism, is caused by adrenocorticotropic hormone (ACTH)-secreting pituitary tumours. Affected humans and dogs have similar clinical manifestations, however, the incidence of the canine disease is thousand-fold higher. This makes the dog an obvious model for studying the pathogenesis of pituitary-dependent hyperadrenocorticism. Despite certain similarities identified at the molecular level, the question still remains whether the two species have a shared oncogenetic background. Recently, hotspot recurrent mutations in the gene encoding for ubiquitin specific protease 8 (USP8) have been identified as the main driver behind the formation of ACTH-secreting pituitary adenomas in humans. In this study, we aimed to verify whether USP8 mutations also play a role in the development of such tumours in dogs.

Methods

Presence of USP8 mutations was analysed by Sanger and PCR-cloning sequencing in 38 canine ACTH-secreting adenomas. Furthermore, the role of USP8 and EGFR protein expression was assessed by immunohistochemistry in a subset of 25 adenomas.

Results

None of the analysed canine ACTH-secreting adenomas presented mutations in the USP8 gene. In a subset of these adenomas, however, we observed an increased nuclear expression of USP8, a phenotype characteristic for the USP8 mutated human tumours, that correlated with smaller tumour size but elevated ACTH production in those tumours.

Conclusions

Canine ACTH-secreting pituitary adenomas lack mutations in the USP8 gene suggesting a different genetic background of pituitary tumourigenesis in dogs. However, elevated nuclear USP8 protein expression in a subset of tumours was associated with a similar phenotype as in their human counterparts, indicating a possible end-point convergence of the different genetic backgrounds in the two species. In order to establish the dog as a useful animal model for the study of CD, further comprehensive studies are needed.

Dynamic computed tomography of the pituitary gland using a single slice scanner in dogs with pituitary-dependent hypercortisolism

Selective removal of the pituitary adenoma has not been advocated in dogs with pituitary-dependent hypercortisolism because the pituitary adenoma is usually not visualized on routine computed tomography (CT). Dynamic pituitary CT scanning is aimed at the detection of the pituitary flush and, indirectly, at the presence and position of the adenoma. The first aim of this retrospective study was to compare findings of a multiple slice dynamic scanning protocol with those of a single slice dynamic protocol using a single slice CT scanner. The second aim was to compare the CT findings with surgical findings, and surgical findings with histopathological findings. Computed tomography with single and multiple slice dynamic scanning protocols was performed in 86 dogs with pituitary-dependent hypercortisolism. Thirty dogs underwent transsphenoidal hypophysectomy and pituitary specimens were collected as tumor, normal, mixed and neurohypophyseal samples and processed for histology. The pituitary flush was not detected more frequent in multiple slice dynamic scanning series than in single slice dynamic scanning series. However, in non-enlarged pituitaries, the flush was seen significantly more frequently than in enlarged pituitaries. Prediction of the nature of the tissue during hypophysectomy by the surgeon was inconclusive. In conclusion, when using a single slice CT scanner, both single or multiple slice dynamic scanning protocols can be used for localization of the neurohypophyseal flush, and, indirectly, the adenoma. However, based on this study, the aim of surgery in dogs with pituitary-dependent hypercortisolism remains total adenohypophysectomy, and when the neurophypophysis is recognized, it may be left in situ.

A magnetic resonance imaging-based classification system for indication of trans-sphenoidal hypophysectomy in canine pituitary-dependent hypercortisolism

OBJECTIVES

The objectives of this study were to establish a magnetic resonance imaging-based classification system for canine hyperadrenocorticism according to pituitary gland extension, determine indications for trans-sphenoidal hypophysectomy, and clarify the prognosis for each disease grade.

METHODS

A 5-point classification system (Grades 1 to 5) was developed based on tumour extension in dorsal and cranio-caudal directions. Cases were then classified as Type A: no arterial circle of Willis or cavernous sinus involvement and Type B: cases in which these blood vessels were involved.

RESULTS

Medical records and magnetic resonance imaging data of 37 cases with hyperadrenocorticism were reviewed. Thirty-three cases underwent surgery; 4 Grade 5 cases did not have appropriate indications for surgery, and other therapies were used. Complete resection was achieved for 3, 3, 22 and 1 Grade 1A, 2A, 3A and 3B cases, respectively. Resection was incomplete in 1, 1 and 2 Grade 3A, 3B and 4B cases, respectively. Remission was achieved in 29 cases. Recurrence occurred in 4 cases, all of which were classified as Grade 3.

CLINICAL SIGNIFICANCE

Dogs with Type A, Grade 1 to 3 hyperadrenocorticism had a good prognosis following trans-sphenoidal hypophysectomy. Grade 3B, 4 and 5 cases may not be suitable for this surgery.

The prognostic value of perioperative profiles of ACTH and cortisol for recurrence after transsphenoidal hypophysectomy in dogs with corticotroph adenomas

BACKGROUND

Transsphenoidal hypophysectomy is an effective treatment for dogs with pituitary-dependent hypercortisolism (PDH). However, long-term recurrence of hypercortisolism is a well-recognized problem, indicating the need for reliable prognostic indicators.

OBJECTIVES

The aim of this study was to evaluate the prognostic value of perioperative plasma ACTH and cortisol concentrations for identifying recurrence of hypercortisolism after transsphenoidal hypophysectomy.

ANIMALS

A total of 112 dogs with PDH that underwent transsphenoidal hypophysectomy met the inclusion criteria of the study.

METHODS

Hormone concentrations were measured preoperatively and 1-5 hours after surgery. Both absolute hormone concentrations and postoperative concentrations normalized to preoperative concentrations were included in analyses. The prognostic value of hormone concentrations was studied with Cox's proportional hazard analysis.

RESULTS

Median follow-up and disease-free period were 1096 days and 896 days, respectively. Twenty-eight percent of patients had recurrence, with a median disease-free period of 588 days. Both absolute and normalized postoperative cortisol concentrations were significantly higher in dogs with recurrence than in dogs without recurrence. High ACTH 5 hours after surgery, high cortisol 1 and 4 hours after surgery, high normalized ACTH 3 hours after surgery, high normalized cortisol 4 hours after surgery and the random slope of cortisol were associated with a shorter disease-free period.

CONCLUSIONS AND CLINICAL IMPORTANCE

Individual perioperative hormone curves provide valuable information about the risk of recurrence after hypophysectomy. However, because no single cutoff point could be identified, combination with other variables, such as the pituitary height/brain area (P/B) ratio, is still needed to obtain a good estimate of the risk for recurrence of hypercortisolism after hypophysectomy.

Expression and clinical relevance of paired box protein 7 and sex determining region Y-box 2 in canine corticotroph pituitary adenomas

Pituitary-dependent hypercortisolism is a common endocrinopathy in dogs, caused by an adrenocorticotrophic hormone secreting pituitary tumour of the anterior or intermediate lobe. The prognosis of intermediate lobe adenomas is worse than that of anterior lobe adenomas, indicating the possible usefulness of melanotropic markers as prognosticators. Another possible origin of pituitary adenomas is found in cancer stem cells. The aim of the present study was to investigate the expression of melanotroph specific transcription factor paired box protein 7 (Pax7) and stem cell marker and reprogramming factor sex determining region Y-box 2 (Sox2) and to relate their expression to clinical parameters. The mean ± SD of labelling index (LI) for Pax7 was 8.6% ± 21.7% in the adenomas; 1/6 controls had positive staining (LI, 15.2%). For Sox2, the LI in the adenomas was 16.9% ± 15.2% and 19.5% ± 11.6% in the controls. Pax7 expression was significantly higher in enlarged pituitaries, compared to non-enlarged pituitaries (P = 0.05), but Pax7 or Sox2 immunopositivity did not correlate to other clinical parameters such as histological diagnosis, survival time or disease-free interval. Gene expression of Pax7 target genes, such as proconvertase 2 (PC2), pro-opiomelanocortin (POMC), and dopamine D2 receptor (DRD2), was significantly lower in the adenoma samples compared to normal tissue, indicating that Pax7 signalling was not activated in adenomas. It was suggested that Pax7 and Sox2 remain interesting targets for molecular investigations into their role in pituitary tumorigenesis, but were unsuitable as clinical prognosticators in dogs.

Syndrome of inappropriate antidiuretic hormone secretion in a cat with a putative Rathke's cleft cyst

An 11-year-old spayed female domestic shorthair cat was evaluated for anorexia, lethargy and weight loss of 6 days' duration. Bilateral mydriasis, absent menace response, slow-to-absent pupillary light reflexes, bilateral retinal detachment, intermittent horizontal nystagmus, intermittent ventral strabismus and systemic hypertension were present. Biochemical analysis revealed severe hyponatremia, severe hypochloremia and mild hypokalemia. Multifocal central nervous system disease was suspected based on optic, trigeminal sensory (ophthalmic branch), vestibulocochlear and possible oculomotor nerve dysfunction. Thoracic radiographs showed mild cardiomegaly without evidence of congestive heart failure. Ultrasound revealed mild pleural and peritoneal effusion. A cause of the severe hyponatremia was not identified, and it persisted despite fluid therapy. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) was suspected as the cause of hyponatremia. Humane euthanasia was elected owing to continued clinical decline. Serum hyposmolality, urine hyperosmolality, natriuresis and lack of confirmed renal, thyroid and pulmonary disease aided in the presumed diagnosis of SIADH. Post-mortem histopathology of the brain revealed degeneration of the hypothalamus and optic tracts, along with a prominent fluid-filled craniopharyngeal duct (putative Rathke's cleft cyst) separating the pars distalis and the pars intermedius. The hypothalamic degeneration, possibly secondary to a Rathke's cleft cyst, was hypothesized to be the cause of presumptive SIADH in the patient. Although rare in occurrence, Rathke's cleft cyst should be included as a differential diagnosis in dogs and cats with signs of pituitary dysfunction.

Severe hyperthermia, hypernatremia, and early postoperative death after transethmoidal cavitron ultrasonic surgical aspirator (CUSA)-assisted diencephalic mass removal in 4 dogs and 2 cats

OBJECTIVE

To report clinical findings including severe hyperthermia and hypernatremia after transethmoidal Cavitron ultrasonic surgical aspirator (CUSA)-assisted diencephalic mass removal.

STUDY DESIGN

Retrospective case series.

ANIMALS

Dogs (n = 4) and 2 cats.

METHODS

Medical records (1997-2003) of dogs and cats that had transethmoidal CUSA-assisted diencephalic mass removal were reviewed. Retrieved data were: history, signalment, blood work, neurologic examination findings, MRI results, histopathology, postoperative complications, pre- and postoperative medical therapy, and outcome.

RESULTS

Tumor types included: meningioma (n = 3), choroid plexus papilloma (1), astrocytoma (1), and pituitary macroadenoma (1). Median onset of hyperthermia was 3.5 hours (range: 1-6 hours) after extubation; median high temperature at onset was 40.3°C, (range: 39.6-41.7°C). Median onset of hypernatremia (median, 172 mmol/L; range: 168-196 mmol/L) was 4.5 hours (range: 1-9 hours) after extubation. Median time of death after hyperthermia was 10.5 hours (range: 6-13 hours) and after extubation was 13.5 hours (range: 11-15 hours).

CONCLUSIONS

Transethmoidal CUSA-assisted diencephalic mass removal is associated with early postoperative hyperthermia, hypernatremia, and death, and cannot be recommended.

Complete surgical removal of a very enlarged pituitary corticotroph adenoma in a dog

A 13 yr old castrated male vizsla was referred to the authors' institute because of polyuria, polydipsia, polyphagia, and weight loss. Pituitary-dependent hypercortisolism (PDH) was diagnosed by hormone testing and adrenal and pituitary imaging. Computed tomography (CT) revealed a pituitary mass measuring 21 mm in width. Medical therapy was initiated with trilostane. Despite adequate control of the hypercortisolemia, the polyuria and polydipsia persisted and the dog developed neurologic signs due to the pituitary mass effect. Pituitary transsphenoidal debulking surgery was performed and immunocytochemistry confirmed a corticotroph adenoma. The dog survived for 13 mo after surgery. Postmortem examination revealed an empty fossa without pituitary remnants and the presence of a malignant pheochromocytoma in the right adrenal gland. This case report demonstrates, for the first time, that a large pituitary adenoma in the dog may be treated successfully by pituitary surgery.

Transsphenoidal surgery using a high definition video telescope for pituitary adenomas in dogs with pituitary dependent hypercortisolism: methods and results

OBJECTIVE

To (1) establish a technique for transsphenoidal removal of pituitary adenomas in dogs with pituitary dependent hypercortisolism (PDH) using a high definition video telescope, and (2) report initial outcomes.

STUDY DESIGN

Prospective case series.

ANIMALS

Dogs with pituitary dependent hypercortisolism (PDH; n = 26) with suprasellar masses.

METHODS

Pituitary tumors were removed using a modification of a transoral transsphenoidal approach. Surgery was observed using a high definition video telescope (VITOM™) and localization of the sella was performed by drilling pilot holes in the basisphenoid bone followed by computed tomography (CT).

RESULTS

Dogs had PDH confirmed by urinary cortisol to creatinine ratio (UCCR) and endogenous ACTH assays, and tumors confirmed by MRI. There were no postoperative cerebrospinal fluid leaks, wound dehiscence, or surgical site infections. Overall postoperative mortality was 19% with no mortality observed in the last 16 dogs, indicating an initial "learning curve" followed by good surgical results. All dogs that survived the immediate postoperative period (1 week) returned to their owners in good health, on hormonal replacement therapy. Follow-up ranged from 3 to 36 months. Sustained tumor control and hormonal remission based on normalized ACTH and UCCR measurements were observed in 20/21 (95%) dogs at 1-year follow-up.

CONCLUSIONS

Modifications of a trans-oral transsphenoidal technique for surgical removal of pituitary tumors provides a safe and effective strategy for long-term remission of PDH with acceptable morbidity and mortality.

Vitamin D status before and after hypophysectomy in dogs with pituitary-dependent hypercortisolism

Both spontaneous hypercortisolism and chronic glucocorticoid treatment are associated with osteoporosis and low circulating concentrations of 1,25-dihydroxy-vitamin D in humans. Pituitary-dependent hypercortisolism (PDH) is a common disorder in dogs, but little is known about the vitamin D status of affected dogs. Pituitary-dependent hypercortisolism in dogs can be treated effectively by hypophysectomy and subsequent hormone supplementation. Because hormone supplementation does not include GH, dogs that have undergone hypophysectomy have low circulating concentrations of GH and IGF-1, which may result in low plasma 1,25-dihydroxy-vitamin D concentrations and consequently increased parathyroid hormone secretion. The aim of this study was to determine whether dogs with PDH need vitamin D supplementation before and/or after hypophysectomy. To this end, we measured plasma concentrations of GH, IGF-1, parathyroid hormone, calcium, phosphate, and vitamin D metabolites in 12 dogs with PDH before and 8 wk after hypophysectomy and in 12 control dogs. Although plasma GH concentrations were lower in dogs with PDH than in control dogs both before and after hypophysectomy, the vitamin D status was similar. In conclusion, there is no need for vitamin D supplementation in dogs with PDH, either before or after hypophysectomy.

Ki-67 and minichromosome maintenance-7 (MCM7) expression in canine pituitary corticotroph adenomas

Pituitary-dependent hyperadrenocorticism (PDH) caused by pituitary corticotroph adenoma is a common endocrine disorder in dogs. The ratio between pituitary height and the area of the brain (P/B) has been used to evaluate the pituitary size. A P/B ratio > 0.31 indicates an enlarged pituitary, whereas a P/B ratio ≤ 0.31 indicates a nonenlarged pituitary. The aim of this study was to investigate the expression of proliferation markers Ki-67 and minichromosome maintenance-7 (MCM7) in canine corticotroph adenomas in enlarged and in nonenlarged pituitaries and to evaluate their relation with the size of canine pituitary corticotroph adenomas. Ki-67 and MCM7 expression in ACTH-positive tumor cells was determined by dual-labeling immunohistochemistry in resected corticotroph adenomas from 15 dogs with PDH. The mean ± SD Ki-67 labeling index (LI) was 0.55% ± 0.59% in corticotroph adenomas with nonenlarged pituitaries and 1.6% ± 0.6% in adenomas with enlarged pituitaries. The MCM7 LI in corticotroph adenomas with nonenlarged pituitaries and in adenomas with enlarged pituitaries was 2.9% ± 2.2% and 10.9% ± 3.7%, respectively. The Ki-67 LI and MCM7 LI were significantly greater in the adenomas with enlarged pituitaries than in the adenomas with nonenlarged pituitaries (P < 0.01 and P < 0.01, respectively). The MCM7 LI was significantly greater than the Ki-67 LI in adenomas (P < 0.01). The Ki-67 LI was positively correlated with the MCM7 LI (r = 0.820, P < 0.01), and the P/B ratio was positively correlated with the Ki-67 LI (r = 0.560, P = 0.03) and the MCM7 LI (r = 0.854, P < 0.01). In conclusion, canine corticotroph adenomas in enlarged pituitaries show greater proliferation potential than do adenomas in nonenlarged pituitaries. MCM7 expression was significantly greater than Ki-67 expression in canine pituitary corticotroph adenomas. Thus, MCM7 may be superior to Ki-67 as a proliferation marker in pituitary tumors.

Central diabetes insipidus after transsphenoidal surgery in dogs with Cushing's disease

Transsphenoidal surgery (TSS) is an effective treatment for canine Cushing's disease, as well as human Cushing's disease. In humans, only the pituitary adenoma tissue is resected by TSS. However, in dogs, the whole pituitary including normal tissue is resected. Hence, central diabetes insipidus (CDI) may complicate the postoperative course in almost all dogs with Cushing's disease treated by TSS. However, it is difficult to assess the duration of the postoperative CDI, and whether it may be transient or permanent. In this study, postoperative CDI in 21 dogs with Cushing's disease and its predicted prognosis by preoperative parameters was investigated. In this study, CDI after TSS was classified as either transient or permanent based on the requirement for desmopressin. Preoperative circulating serum cortisol concentrations and pre- and post-operative plasma AVP concentrations were not significantly different between the transient CDI dogs and permanent CDI dogs. The duration of postoperative CDI was not correlated to the signal intensity ratio (posterior lobe of the pituitary/cerebral cortex), which is obtained from preoperative magnetic resonance imaging (MRI). However, the pituitary height/brain area (P/B) ratio of the permanent CDI dogs was significantly greater than that of the transient CDI dogs. In addition, there was a significant difference between the enlarged-pituitary (P/B ratio > 0.31) transient CDI dogs and the permanent CDI dogs. These results suggest that the incidence of postoperative permanent CDI is strongly influenced by the pituitary size.

Expression of Ki-67, PCNA, and p27kip1 in canine pituitary corticotroph adenomas

Pituitary-dependent hypercortisolism (PDH), which is caused by adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas, is a common endocrinopathy in dogs. Dogs with non-enlarged pituitaries harboring a microadenoma have a better prognosis than those with enlarged pituitaries. The aim of this study was to investigate the expression of the proliferation markers Ki-67 and proliferating cell nuclear antigen (PCNA) and the cell-cycle inhibitor p27kip1 in corticotroph adenomas in enlarged and non-enlarged pituitaries. The expression of Ki-67, PCNA, and p27kip1 was analyzed by immunohistochemical staining of 17 pituitary adenoma samples harvested during pituitary surgery in dogs with PDH. The labeling index was calculated by counting the number of immunopositive cells per 1,000 cells. The mean (+/- standard deviation) labeling index for Ki-67 was 8.4%+/-14.2% for the group with enlarged pituitaries, and 8.8%+/-5.5% for the group with non-enlarged pituitaries; that for PCNA was 35.5%+/-12.2% and 37.0%+/-15.5%; and that for p27kip1 was 29.3%+/-22.6% and 42.5%+/-27.9%, respectively. No significant differences in Ki-67, PCNA, and p27kip1 labeling indices were found between enlarged and non-enlarged pituitaries. However, a trend toward significance was observed when comparing the expression of p27kip1 in enlarged pituitaries versus normal pituitary tissue. It is concluded that Ki-67 and PCNA are not useful as proliferative markers for studying the pathobiology of pituitary corticotroph adenomas in dogs.

Efficacy of transsphenoidal surgery on endocrinological status and serum chemistry parameters in dogs with Cushing's disease

Postoperative changes in endocrinological status and serum chemistry during the 4 years after transsphenoidal surgery (TSS) in 25 dogs with Cushing's disease were investigated in a prospective study. In all 25 dogs, Cushing's disease was diagnosed from resected pituitary tissues as a corticotroph adenoma in the anterior lobe of the pituitary. Prior to TSS, all 25 dogs showed hypercortisolemia. After TSS, the ACTH stimulation test showed continued low serum cortisol concentrations in 21 dogs (84%). In addition, the serum thyroid stimulating hormone concentrations decreased sequentially, while the serum T4 concentrations tended to increase due to the postoperative hormone substitution therapy utilized to avoid secondary hypothyroidism. In regard to serum chemistry, alkaline phosphatase (ALP), alanine aminotransferase (ALT) and total cholesterol are commonly increased in canine Cushing's disease. In this study, ALP, ALT and total cholesterol were increased in 23 cases (92%), 19 cases (76%) and 20 cases (80%), respectively. However, postoperatively, these concentrations gradually decreased. The postoperative serum concentrations of ALP at 1 year, that of ALT at six months to 2 years and that of total cholesterol over the course of the 4 years decreased significantly compared with the concentrations before TSS. These results show that TSS is an effective treatment for canine Cushing's disease and for long-term improvement of hypercortisolemia. Moreover, TSS is effective in improvement of hypercortisolism, such as increased concentrations of serum ALP, ALT and total cholesterol.

Hypophysectomy for a dog with coexisting Cushing's disease and diabetes mellitus

An 11-year-old male mixed breed dog diagnosed with Cushing's disease and diabetes mellitus was treated by hypophysectomy. After surgery, the hypercortisolemia disappeared and the diabetes status improved. The insulin requirement to control hyperglycemia gradually decreased. At 12 weeks after surgery, there was no requirement for insulin and we suspected the diabetes was completely resolved. In the present case, diabetes mellitus seems to be secondary to Cushing's disease. In conclusion, this mixed breed dog with coexisting Cushing's disease and diabetes mellitus is the first case showing the effectiveness of hypophysectomy to treat diabetes mellitus secondary to Cushing's disease in dogs.

Computed tomography and low-field magnetic resonance imaging of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism: 11 cases (2001-2003)

OBJECTIVE

To compare the results of computed tomography (CT) and magnetic resonance imaging (MRI) of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism (PDH) caused by histologically confirmed pituitary adenoma.

DESIGN

Retrospective case series.

ANIMALS

11 dogs with PDH that underwent transsphenoidal hypophysectomy.

PROCEDURES

Medical records of dogs examined between January 2001 and March 2003 were reviewed. Dogs were included in this study if they had clinical signs of hypercortisolism at the time of admission (for which PDH was diagnosed) and underwent transsphenoidal hypophysectomy. Pre- and postcontrast CT and low-field MRI (0.2-Tesla magnet) were performed on the same day as surgery for each dog.

RESULTS

An abnormal pituitary gland was found in 7 dogs by use of MRI and in the same 7 dogs by use of CT. Significant differences were found between postcontrast CT and MR images for height, width, and length of the pituitary gland; brain area; and thickness of the sphenoid bone. However, the pituitary gland height-to-brain area ratio determined from postcontrast CT and MR images was not significantly different. The signal-to-noise ratio and contrast-to-noise ratio of pre- and postcontrast MR images were significantly higher than those of the CT images.

CONCLUSIONS AND CLINICAL RELEVANCE

Low-field MRI and dynamic CT imaging of the pituitary gland provided comparable information on the presence of pituitary adenomas in dogs with PDH.

Expression of genes related to corticotropin production and glucocorticoid feedback in corticotroph adenomas of dogs with Cushing's disease

Cushing's disease caused by pituitary corticotroph adenoma is a common endocrine disease in dogs. A characteristic biochemical feature of corticotroph adenomas is their relative resistance to negative feedback by glucocorticoids. In this study, we examined gene expression related to adrenocorticotropic hormone (ACTH) production and secretion, and the negative feedback by glucocorticoids in canine corticotroph adenoma. We used resected corticotroph adenomas from 10 dogs with Cushing's disease. In order to investigate the alteration of gene expression between corticotroph adenoma and normal corticotrophic cells, ACTH-positive cells in the anterior lobe were microdissected using a laser-capture microdissection system, and mRNA levels of proopiomelanocortin (POMC), corticotropin releasing hormone receptor 1 (CRHR1), glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and 11 beta hydroxysteroid dehydrogenase (11HSD) type 1 and type 2 were determined using real-time RT-PCR. POMC, CRHR1, and 11HSD2 mRNA levels in corticotroph adenoma were greater than those in normal corticotrophic cells (POMC, 5.5-fold; CRHR1, 4.9-fold; 11HSD2, 4.2-fold, P<0.01, respectively). MR and 11HSD1 mRNA levels in corticotroph adenoma were lower than those in normal corticotrophic cells (MR, 2.2-fold; 11HSD1, 2.9-fold, P<0.01, respectively). GR mRNA levels did not differ between corticotroph adenoma and normal corticotrophic cells. Our results may help to understand the increased ACTH production and the resistance to negative feedback suppression by glucocorticoids in canine corticotroph adenomas. These changes in gene expression may have a role in the growth of canine corticotroph adenoma, and help elucidate the pathophysiology of dogs with Cushing's disease.

Cushing's disease complicated with thrombosis in a dog

Thrombosis is a potential complication of hyperadrenocorticism (HAC) in dogs. An 8-year-old male Beagle diagnosed with pituitary-dependent HAC had complicated with thrombosis in the caudal vena cava and abdominal aorta, which was treated by hypophysectomy and antithrombotic therapy. After hypophysectomy, hypercortisolemia disappeared and the general condition was also significantly improved. Ultrasonography after hypophysectomy revealed that the thrombus remained in the abdominal aorta, but the thrombus in the caudal vena cava had disappeared. However 692 days after the hypophysectomy, the dog had an acute onset of dyspnea and died. Postmortem examination revealed the presence of thrombi in the abdominal aorta and the pulmonary artery. Observations from this case show that HAC dogs must be attention to thrombosis.

Expression and functional analysis of dopamine receptor subtype 2 and somatostatin receptor subtypes in canine cushing's disease

Cushing's disease (CD) is a severe disorder characterized by chronic hypercortisolism due to an ACTH-secreting pituitary adenoma. Transsphenoidal adenomectomy is the treatment of choice in humans with CD, but recurrences occur frequently. Finding an effective and safe medical treatment for CD may improve long-term clinical outcome. The recent demonstration of expression of somatostatin receptor subtypes (mainly sst5) and dopamine receptor subtype 2 (D2) in human corticotroph adenomas offers the possibility for medical treatment of CD with novel somatostatin analogs and dopamine agonists. Investigation of the effects of these drugs is hampered by the low incidence of CD in humans. Interestingly, CD is a frequent disorder in dogs with striking clinical similarities with CD in humans. Therefore, we investigated the expression and functional role of D2 and somatostatin receptors in corticotroph adenoma cells from 13 dogs with active CD that underwent therapeutic hypophysectomy and normal anterior pituitary cells from five dogs. Quantitative RT-PCR and immunohistochemistry revealed that both in CD and normal anterior pituitary, sst2 was the predominant receptor subtype expressed, whereas D2 was modestly expressed and sst5 was expressed only at very low levels. In primary cultures of canine adenomas (n = 7), the sst2-preferring agonist octreotide also showed the strongest ACTH-suppressive effects. In conclusion, canine corticotroph adenomas provide an interesting model to study CD, but differences in somatostatin and dopamine receptor expression between humans and dogs should be taken into account when using dogs with CD as a model to evaluate efficacy of novel somatostatin analogs and dopamine agonists for human CD.

Expression and mutation analysis of Tpit in the canine pituitary gland and corticotroph adenomas

Pituitary-dependent hyperadrenocorticism (PDH) in dogs is caused by a pituitary corticotroph adenoma. Although PDH is a common disorder in dogs, little is known about the underlying pathogenesis. In the pituitary glands of humans and mice, the pro-opiomelanocortin (POMC)-expressing cell lineages, the corticotrophs and melanotrophs, have a specific marker in common, the T-box transcription factor Tpit (Tbx19), which is obligate for POMC expression. Tpit also regulates the late differentiation of the corticotrophs and melanotrophs, and therefore may contribute to the pathogenesis of the corticotroph adenomas. The aim of this study was to perform an expression and mutation analysis of Tpit in the normal canine pituitary and in corticotroph adenomas. The distribution of the Tpit protein in the pituitary gland was studied with immunohistochemistry and the expression of the gene with RT-PCR. The coding region of Tpit cDNA from 14 dogs with PDH was screened for mutations. Tpit was expressed in corticotroph and melanotroph cells of the normal and adenomatous canine pituitary, and remained present in non-adenomatous corticotrophs of pituitaries from PDH dogs. No tumor-specific mutation in the Tpit cDNA from the corticotroph adenomas was found. However, a missense polymorphism in the highly conserved DNA-binding domain, the T-box, was discovered in one dog. It is concluded that Tpit can be used as a reliable marker for the corticotroph and melanotroph cells in the canine pituitary tissue and that mutations in the Tpit gene are unlikely to play a major role in the pathogenesis of canine corticotroph adenomas.

Prognostic factors for outcome after transsphenoidal hypophysectomy in dogs with pituitary-dependent hyperadrenocorticism

Object

The aim of this study was to determine prognostic factors for outcome after transsphenoidal hypophysectomy in dogs with pituitary-dependent hyperadrenocorticism (PDH).

Methods

One veterinary neurosurgeon performed transsphenoidal hypophysectomies in 181 dogs with PDH over a 12-year period. Survival analysis was performed with the Kaplan–Meier method. Prognostic factors were analyzed with the univariate Cox proportional hazard analysis followed by stepwise multivariate analysis. The log-rank test was used to assess disease-free fractions in three groups categorized according to early postoperative urinary corticoid/creatinine (C/C) ratios.

Results

Multivariate analysis revealed that old age, large pituitary size, and high preoperative concentrations of plasma adrenocorticotropic hormone were associated with an increased risk of PDH-related death. In addition, large pituitary size, thick sphenoid bone, high C/C ratio, and high concentration of plasma α-melanocyte–stimulating hormone (α-MSH) before surgery were associated with an increased risk of disease recurrence in the dogs that went into remission after hypophysectomy. Disease-free fractions were significantly higher in dogs with postoperative urinary C/C ratios in the lower normal range (< 5 × 10−6) than in dogs with postoperative C/C ratios in the upper normal range (5–10 × 10−6).

Conclusions

The results of this study indicate that pituitary size, sphenoid bone thickness, plasma α-MSH concentration, and preoperative level of urinary cortisol excretion are predictors of long-term remission after transsphenoidal hypophysectomy for PDH in dogs. Urinary C/C ratios measured 6 to 10 weeks after surgery can be used as a guide for predicting the risk of tumor recurrence.

Thin-slice three-dimensional gradient-echo magnetic resonance imaging of the pituitary gland in healthy dogs

OBJECTIVE

To evaluate thin-slice 3-dimensional gradient-echo (GE) magnetic resonance imaging (MRI) of the pituitary gland in healthy dogs.

ANIMALS

11 healthy dogs.

PROCEDURES

By use of a 0.2-Tesla open magnet, MRI of the skull was performed with T1-weighted GE sequences and various protocols with variations in imaging plane, slice thickness, and flip angle before and after administration of contrast medium; multiplanar reconstructions were made. The pituitary region was subjectively assessed, and its dimensions were measured. Image quality was determined by calculation of contrast-to-noise and signal-to-noise ratios.

RESULTS

Best-detailed images were obtained with a T1-weighted GE sequence with 1-mm slice thickness and 30 degrees flip angle before and after administration of contrast medium. Images with flip angles > 50 degrees were of poor quality. Quality of multiplanar reconstruction images with 1-mm slices was better than with 2-mm slices. The bright signal was best seen without contrast medium. With contrast medium, the dorsal border of the pituitary gland was clearly delineated, but lateral borders were more difficult to discern.

CONCLUSIONS AND CLINICAL RELEVANCE

MRI of the canine pituitary gland with a 0.2-Tesla open magnet should include a T1-weighted GE sequence with 1-mm slice thickness and flip angle of 30 degrees before and after administration of contrast medium. The neurohypophysis was best visualized without contrast medium. The MRI examination permitted differentiation between the pituitary gland and surrounding structures.

Functional and morphological changes in the hypothalamus-pituitary posterior lobe system after hypophysectomy in the dog

Acute diabetes insipidus-like symptoms have been reported as a complication after hypophysectomy in dogs. These symptoms are believed to be the consequence of deficiency of arginine vasopressin (AVP) secretion. The symptoms spontaneously resolve within 2 weeks, but the mechanism is unclear. In the present study, AVP secretion related to increases in Na+ concentration and serum osmotic pressure was measured, and immunohistochemical analysis in the paraventricular and supraoptic nuclei was performed after hypophysectomy in normal dog. In the hypertonic saline test, the plasma AVP concentration slightly increased in hypophysectomized dogs, although the increase was markedly smaller than that in normal dogs. An immunohistochemical study of the hypothalamus nucleus revealed that, AVP-positive cells tended to decrease after hypophysectomy. It suggests that excision of the posterior lobe by surgery injured the axon of magnocellular neuron in the hypothalamus. A decrease in the function and the number of AVP-producing and -secreting magnocellular neurons after hypophysectomy, suggests that the clinical improvement of postoperative diabetes insipidus-like symptoms may not be related to the recovery of AVP secretion.

Canine Hypophysectomy Using a Ventral Paramedian Approach

OBJECTIVE

To evaluate the degree of pituitary exposure, completeness of hypophysectomy, and perioperative morbidity associated with an alternative paramedian surgical approach and excisional technique for the canine pituitary gland.

STUDY DESIGN

Experimental imaging, surgical, and endocrinologic study.

ANIMAL POPULATION

Nine healthy, purpose-bred Beagle dogs.

METHODS

Surgical landmarks for the pituitary were determined by computed tomography (CT), and then using a ventral paramedian approach medial to the rami of the mandible, the pituitary was exposed and removed en bloc by manipulation and ultrasonic aspiration. Efficacy of the procedure was evaluated using endocrinologic and pathologic observation.

RESULTS

CT images allowed the precise location of surgical landmarks for hypophysectomy. Statistically significant decreases in secretion of all measured pituitary hormones except adrenocorticotropic hormone (ACTH) occurred after hypophysectomy. Despite the absence of gross evidence of residual pituitary tissue, immunohistochemical staining revealed residual pituitary cells in the sella turcica of most dogs.

CONCLUSION

CT imaging and a paramedian approach facilitated surgical access to the pituitary gland by a transoral technique; however, use of an ultrasonic aspirator removed all visible pituitary glands but left cellular remnants capable of ACTH secretion in the sella turcica.

CLINICAL RELEVANCE

Although this technique did not result in complete hypophysectomy, clinical use in dogs with pituitary-dependent hyperadrenocorticism is warranted because the goal is not complete hypophysectomy but removal of a pituitary tumor.