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

An Illustrated Scoping Review of the Magnetic Resonance Imaging Characteristics of Canine and Feline Brain Tumors

Magnetic resonance imaging (MRI) is used pervasively in veterinary practice for the antemortem diagnosis of intracranial tumors. Here, we provide an illustrated summary of the published MRI features of primary and secondary intracranial tumors of dogs and cats, following PRISMA scoping review guidelines. The PubMed and Web of Science databases were searched for relevant records, and input from stakeholders was solicited to select data for extraction. Sixty-seven studies of moderate to low-level evidence quality describing the MRI features of pathologically confirmed canine and feline brain tumors met inclusion criteria. Considerable variability in data inclusion and reporting, as well as low case numbers, prohibited comparative data analyses. Available data support a holistic MRI approach incorporating lesion number, location within the brain, shape, intrinsic signal appearances on multiparametric sequences, patterns of contrast enhancement, and associated secondary changes in the brain to prioritize differential imaging diagnoses, and often allows for accurate presumptive diagnosis of common intracranial tumors. Quantitative MRI techniques show promise for improving discrimination of neoplastic from non-neoplastic brain lesions, as well as differentiating brain tumor types and grades, but sample size limitations will likely remain a significant practical obstacle to the design of robustly powered radiomic studies. For many brain tumor variants, particularly in cats, there remains a need for standardized studies that correlate clinicopathologic and neuroimaging data.

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.

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.

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.

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.

Sequential Treatment of a Large Pituitary Corticotroph Neoplasm and Associated Neurological Signs in a Dog

No standardized treatment guidelines are reported in veterinary medicine for dogs with large pituitary corticotroph neoplasms causing neurological signs, and such dogs usually have a short overall survival. When these dogs undergo pituitary surgery and the tumor regrows there are few reports of subsequent treatments. A 7 yr old male Maltese diagnosed with pituitary-dependent hypercortisolism developed seizures in conjunction with a large pituitary corticotroph adenoma and underwent transsphenoidal hypophysectomy. After 3 yr of clinical remission, hypercortisolism recurred, and trilostane therapy was initiated. One year later, the dog developed new neurological signs and computed tomography revealed regrowth of a large pituitary mass that was then treated with radiation therapy. The dog lived disease-free for 3 more yr. At postmortem examination, a more aggressive pituitary neoplasm than the one examined at the time of surgery was found, which is suggestive of malignant transformation into a carcinoma despite the absence of convincing metastasis.

Pathological Findings in the Pituitary Glands of Dogs and Cats

With the exception of classic functional adenomas in dogs and horses, pituitary lesions are infrequently described in the veterinary literature. Approximately 10% of pituitary glands from asymptomatic humans contain abnormalities, but the equivalent proportion in small animals is unknown. Pituitary glands from 136 dogs and 65 cats collected during routine necropsies were examined to determine the prevalence of pituitary lesions and their histopathological diagnosis. Lesions were characterized in sections stained with hematoxylin and eosin, periodic acid-Schiff (PAS), Gordon and Sweet’s and reticulin stains, and immunohistochemistry for adrenocorticotropic hormone (ACTH), growth hormone, melanocyte stimulating hormone–α, and prolactin. Pituitary abnormalities were identified in 36 of 136 (26.4%) dogs and 10 of 65 (15.3%) cats. Cystic changes were the most common lesion, occurring in 18 (13.2%) dogs and 8 (12.3%) cats. Pituitary neoplasia was detected in 14.1% (12/85) of middle-aged and old dogs; 1 (1.5%) cat had pituitary nodular hyperplasia. PAS and reticulin stains helped differentiate ACTH-immunoreactive adenomas from hyperplastic nodules: adenomas contained PAS-positive intracytoplasmic granules and loss of the normal reticulin network. One dog had a pituitary carcinoma with infiltration into the thalamus. Other pituitary abnormalities included secondary metastases (2 dogs) and hypophysitis (4 dogs, 1 cat). In most cases, the lesion appeared to be subclinical and could be considered incidental, whereas clinical manifestations were apparent in only 4 dogs (2.9%) and none of the cats with pituitary lesions. Pituitary abnormalities are common in dogs and cats, and their clinical relevance requires further investigation.

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.