Presumed pituitary apoplexy in 26 dogs: Clinical findings, treatments, and outcomes

BACKGROUND

Pituitary apoplexy refers to hemorrhage or infarction within the pituitary gland resulting in acute neurological abnormalities. This condition is poorly described in dogs.

OBJECTIVES

To document presenting complaints, examination findings, endocrinopathies, magnetic resonance imaging (MRI), treatments, and outcomes of dogs with pituitary apoplexy.

ANIMALS

Twenty-six client-owned dogs with acute onset of neurological dysfunction.

METHODS

Retrospective case series. Dogs were diagnosed with pituitary apoplexy if MRI or histopathology documented an intrasellar or suprasellar mass with evidence of hemorrhage or infarction in conjunction with acute neurological dysfunction. Clinical information was obtained from medical records and imaging reports.

RESULTS

Common presenting complaints included altered mentation (16/26, 62%) and gastrointestinal dysfunction (14/26, 54%). Gait or posture changes (22/26, 85%), mentation changes (18/26, 69%), cranial neuropathies (17/26, 65%), cervical or head hyperpathia (12/26, 46%), and hyperthermia (8/26, 31%) were the most frequent exam findings. Ten dogs (38%) lacked evidence of an endocrinopathy before presentation. Common MRI findings included T1-weighted hypo- to isointensity of the hemorrhagic lesion (21/25, 84%), peripheral enhancement of the pituitary mass lesion (15/25, 60%), brain herniation (14/25, 56%), and obstructive hydrocephalus (13/25, 52%). Fifteen dogs (58%) survived to hospital discharge. Seven of these dogs received medical management alone (median survival 143 days; range, 7-641 days) and 8 received medications and radiation therapy (median survival 973 days; range, 41-1719 days).

CONCLUSIONS AND CLINICAL IMPORTANCE

Dogs with pituitary apoplexy present with a variety of acute signs of neurological disease and inconsistent endocrine dysfunction. Dogs that survive to discharge can have a favorable outcome.

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.

Variation in the MRI appearance of the canine pituitary gland

A recent publication described pathological findings in the pituitary gland incidentally discovered during routine necropsies of the brain of dogs and cats; however, imaging characteristics of these lesions were not reported. Aims of this retrospective, observational study were to characterize MRI variants and incidental lesions in pituitary glands of dogs with no clinical signs of pituitary disease. Cranial MRIs from dogs with no suspicion of pituitary disease, based on history and presenting clinical signs, were retrieved from a veterinary teleradiology database during the period of January 2014 to January 2016. Images were reinterpreted by two observers and pituitary lesions were described based on consensus. A total of 580 scans were evaluated and pituitary lesions were detected in 78 dogs (13.44%). Pituitary cystic lesions were the most common finding and occurred in 31 dogs (5.34%). Of these 31 dogs, the majority (74%) were of toy or brachycephalic breed. Partial or total empty sella lesions were detected in 14 dogs (2.41%), and all of these were small or toy breeds. A significantly increased incidence of the partial empty sella lesion was found in male dogs (P = .034). Pituitary lesions greater than 1 cm occurred rarely (0.69%). There was a significant association between low-field (LF) MRI strength and detection of a partial or total empty sella lesion (P = .0112), and detection of a pituitary lesion greater than 1 cm (P = .0125). A significant difference was present between the MRI field strength (FS) that identified pituitary cysts and the FS that detected an empty sella (P = .0068), with the former being a high FS and the latter a LF strength. The findings from this study indicated that up to 13% of dogs with no presenting clinical signs of pituitary disease may have MRI pituitary lesions.

Mensuration of the rabbit pituitary gland from computed tomography

The aim of this retrospective reference interval observational study was to determine the mensuration of the pituitary gland (hypophysis cerebri) by analyzing CT studies in rabbits without clinical evidence of pituitary disease or central neurologic signs. Though diseases of the rabbit pituitary gland are uncommon, the pituitary gland is essential in regulation of the rabbit's endocrine system, as in other species. Currently, there are minimal published studies that detail the rabbit head anatomy on cross-sectional imaging, and even less specifically examining the pituitary gland. The pituitary gland was measured by one observer at a single time point from transverse and reconstructed sagittal CT images in a soft-tissue algorithm in 62 rabbits for a total of 66 rabbit head CT studies. The rabbits ranged from 0.84 to 14 years in age (mean ± SD: 5.46 ± 3.05 years) and 0.92 to 4.95 kg in weight (2.21 ± 0.83 kg). Linear pituitary measurements were performed using electronic calipers. The mean ± SD pituitary height was 4.22 ± 0.57 mm, width was 4.48 ± 0.71 mm, and length was 6.02 ± 0.70 mm. The pituitary gland height-to-brain area ratio was 1.10 ± 0.16 mm^-1 , which is much higher than the values reported in normal dogs and cats. The age, weight, and sex of the rabbits were not found to have a significant impact on pituitary gland mensuration. These measurements could be useful as a reference range for future rabbit head CT studies and to rule out pituitary enlargement or disease when evaluating rabbit pituitary glands.

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.