Page 905 - Small Animal Internal Medicine, 6th Edition

CHAPTER 50 Disorders of the Adrenal Gland 877

hyperadrenocorticism, and prolonged survival with a good less commonly, permanent central diabetes insipidus (CDI),
quality of life. All studies evaluating the effect of irradiation hypernatremia, keratoconjunctivitis sicca (KCS), and sec-
VetBooks.ir on pituitary tumor size, to date, have documented a signifi- ondary hypothyroidism (Hanson et al., 2005). Postoperative
hormonal replacement therapy included synthetic vasopres-
cant decrease in tumor size in almost all dogs treated.
Prognostic factors that affect survival time after radiation
present until death or until latest follow-up in 22% of the dogs.
therapy include the severity of neurologic signs and the rela- sin (DDAVP), glucocorticoids, and levothyroxine. CDI was
tive size of the tumor. Generally, dogs with subtle or mild In another study, the incidence of postoperative permanent
neurologic clinical signs and the smallest tumors show the CDI in dogs undergoing transsphenoidal surgery for PDH
best response to treatment. Theon et al. (1998) found a mean was strongly influenced by the size of the pituitary tumor;
survival time after radiation of 25 months in dogs with mild the larger the tumor, the more likely for postoperative CDI to
neurologic signs, 17 months in dogs with severe neurologic be permanent (Teshima et al., 2011). Twelve of the 150 dogs
signs, and only 5 months in untreated dogs with neurologic died within 4 weeks of surgery. One-hundred twenty-seven
signs. In a study by Kent et al. (2007), mean survival time in (92%) of 138 dogs that were alive after 4 weeks experienced
19 dogs with pituitary masses treated with radiation therapy remission within 8 weeks of surgery; remission was defined
was 1405 days, and 1-, 2-, and 3-year estimated survival was as resolution of clinical signs of hyperadrenocorticism and
93%, 87%, and 55%, respectively. In contrast, mean survival UCCR values in the reference range. Hyperadrenocorticism
time in 27 untreated dogs with pituitary masses was 551 remained in remission in 95 of 127 dogs (75%). In 32 of 127
days, and 1-, 2-, and 3-year estimated survival was 45%, 32%, dogs (25%), signs of hyperadrenocorticism and increased
and 25%, respectively. UCCR values recurred at 6 weeks to 56 months (median, 18
Because of the high prevalence of a pituitary mass at the months) after surgery. The 1-year, 2-year, 3-year, and 4-year
time PDH is diagnosed and the potential for future growth estimated survival rate was approximately 84%, 76%, 72%,
and development of neurologic signs, we routinely discuss and 68%, respectively. The 1-year, 2-year, 3-year, and 4-year
CT imaging of the pituitary gland as part of the evaluation estimated relapse-free fraction was approximately 88%, 75%,
of a dog with newly diagnosed PDH even if there is no clini- 66%, and 59%, respectively. Survival and disease-free frac-
cal evidence of a large pituitary mass, especially if the client tions of dogs with enlarged pituitaries were significantly
is willing to consider irradiation therapy if a large pituitary lower than in dogs with nonenlarged pituitaries.
mass is identified. Our preference is to perform CT imaging Based on the experiences at Utrecht University, micro-
once clinical signs of hyperadrenocorticism are controlled surgical transsphenoidal hypophysectomy is an effective
with medical treatment. We understand that CT imaging is long-term treatment of PDH in dogs. Early diagnosis of
expensive but many of our clients are interested and want to a corticotroph adenoma is important. Transsphenoidal
know the status of the pituitary mass. No further evaluation hypophysectomy is most effective in dogs with nonenlarged
of the pituitary is indicated if a pituitary mass is not identi- or moderately enlarged pituitaries. Size of the pituitary
fied on the initial CT scan. If a pituitary mass is identified tumor has a direct impact on survival, disease-free fractions,
and measures 3 to 7 mm in greatest vertical height, a repeat and incidence of permanent CDI in dogs. Unfortunately,
pituitary scan is recommended 12 months later. If a pituitary the number of sites currently offering hypophysectomy as
mass is identified equal to or greater than 8 mm in greatest a treatment option for PDH is limited in the United States.
vertical height, pituitary irradiation is recommended. The
goal of pituitary irradiation is to shrink the mass and prevent Prognosis
development of macrotumor syndrome; trilostane or mito- Reported median survival times for dogs with ADH that
tane therapy may still be needed to control clinical signs of survive the initial postadrenalectomy month range from 492
hyperadrenocorticism. to 953 days, with some dogs living 4 to 5 years after surgery
(Schwartz et al., 2008; Lang et al., 2011; Massari et al., 2011).
HYPOPHYSECTOMY In one study by Helm et al. (2011), median survival times
For several decades, selective pituitary microsurgery using for dogs with ADH treated with trilostane and mitotane were
the transsphenoidal approach has been considered the treat- 353 days (95% confidence interval [CI], 95-528 days) and
ment of choice for pituitary tumors causing hyperadreno- 102 days (95% CI, 43-277 days), respectively. Dogs with
corticism in humans. Initial studies in veterinary medicine adrenocortical adenoma or adrenocortical carcinoma that
developing the microsurgical technique, identifying postop- has not metastasized (uncommon) have a good prognosis,
erative complications and assessing postoperative pituitary whereas dogs with metastatic adrenocortical carcinoma or
function, or lack thereof, were done in healthy dogs approxi- carcinoma with vein invasion (common) have a poorer prog-
mately 25 years ago. Since then, Meij and co-investigators at nosis, and these dogs typically succumb to the disease within
Utrecht University, the Netherlands, have published several 1 to 2 years of diagnosis. Although clinical signs can be
articles detailing their experiences with transsphenoidal controlled with trilostane and mitotane, death ultimately
hypophysectomy in dogs with PDH. In 2005, the Utrecht results from the debilitating effects of the tumor, complica-
group reported on the long-term results of transsphenoidal tions of vein thrombosis (e.g., ascites) or metastatic growth,
hypophysectomy in 150 dogs with PDH (Hanson et al., or other geriatric disorders (e.g., chronic kidney disease,
2005). Postoperative complications included transient and, congestive heart failure).