Pituitary Macroadenoma in Dogs with Cushing's Disease: Diagnosis and Management
Mark E Peterson, DVM, Dip. ACVIM
Animal Endocrine Clinic
New York, New York 10025

ABSTRACT: More than 90% of dogs with pituitary-dependent hyperadrenocorticism (PDH) have an ACTH-secreting pituitary adenoma as the primary cause of their disease. Approximately 50%-60% of these dogs with PDH have a pituitary tumor large enough to be visible on CT or MRI scans at the time of diagnosis. Although large pituitary tumors can be found at time of diagnosis, most dogs initially have small pituitary tumors that increase in size over time as they are being treated medically with mitotane or trilsotane. Although these therapies are effective at relieiving the clinical signs associated with the disease, neither treatment targets the pituitary tumor. Therefore, over time, all dogs with PDH are at risk for continued pituitary tumor development, growth, and invasion.

Over the last few years as management of dogs with PDH has improved, affected dogs are living longer, allowing more time for causative ACTH-secreting pituitary tumors to grow. It has been estimated that 15% to 30% of dogs with PDH will eventually develop neurologic signs caused by expansion of their pituitary tumor.


Canine Pituitary Macrotumors
Sarah A.Moore, DVM
Dennis P.O’Brien, DVM, PhD
University of Missouri
January, 2008

ABSTRACT: Pituitary macroadenomas and macroadenocarcinomas are being increasingly recognized in veterinary medicine.The term macroadenoma is poorly defined in veterinary medicine. Because pituitary imaging is not routinely performed in dogs with pituitary-dependent hyperadrenocorticism (PDH), the true incidence of pituitary macroadenomas is unknown but may range from 15% to 75% of dogs with PDH. Recent advances in endocrine testing and pituitary imaging have facilitated the detection of pituitary macrotumors, leaving routine imaging of affected patients as the last hurdle to early detection, treatment, and an improved quality of life.



Diagnosis and Treatment of Pituitary Tumors
Edward C. Feldman, DVM, DACVIM
Professor, School of Veterinary Medicine, Tupper Hall, University of California
Davis, CA, USA
February, 2008

In people, large (macro) sized tumors have usually been defined as those masses >1cm in diameter. We suggest that a second definition be utilized when describing pituitary masses with or without suprasellar extension in dogs: masses which are visible on CT scan, MR imaging, or on gross necropsy be described as “macro” and those which can only be seen microscopically (thus not visualized with CT or MRI) be referred to as “micro.” Further definition of these pituitary masses would depend: 1) on the presence or absence of suprasellar extension and 2) on the presence of absence of clinical signs that could be caused by such a mass.

Following documentation of a “macro” pituitary mass with dorsal extension, the only therapeutic protocol with which we have had success is radiation. Not only is the diagnosis of this disorder difficult and expensive, but treatment may also be extremely expensive. Facilities for radiation are becoming more available. In addition to significant expense, current treatment protocols typically call for daily treatments over 3 to 4 weeks. Thus, these older debilitated dogs must be anesthetized numerous times, incurring considerable stress as well as the expense.

However, we now recommend radiation for any dog with a pituitary tumor >8mm in size, regardless of the clinical signs. Prognosis is better for dogs without clinical signs and those with masses <15mm in size. Larger masses and serious clinical signs have a much poorer prognosis.
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Effects of radiotherapy on pituitary corticotroph macrotumors in dogs: A retrospective study of 12 cases
Pauline de Fornel, Françoise Delisle, Patrick Devauchelle, Dan Rosenberg
Can Vet J 2007;48:481–486

Abstract — The efficacy of low doses of radiotherapy for the treatment of pituitary corticotroph macrotumors in dogs is evaluated retrospectively. Twelve dogs with pituitary-dependent hyperadrenocorticism and a large pituitary tumor treated with 36 Gy of radiation were included. Radiation was delivered in 12 fractions of 3 Gy over a 4- to 6-week period. Effects of radiation therapy on tumor size were assessed by computed tomography scans; a decrease was observed in 11 dogs (decrease . 50% in 6 dogs). Three dogs were reirradiated due to major tumor regrowth or a lack of tumor decrease (mean total dose: 22 Gy given in 3-Gy fractions over 3 or 4 weeks). The mean and median survival times following the initiation of radiotherapy were 22.6 months (688 days) and 17.7 months (539 days), respectively. These data are consistent with previous findings, based on high-dose radiation, showing that radiotherapy is a useful option for treating pituitary corticotroph macrotumors in dogs. Furthermore, computed tomography follow-up of the treated dogs demonstrates objectively the efficacy of radiotherapy against corticotroph tumors in dogs.