Page 89 - Clinical Small Animal Internal Medicine

7 Pituitary-Dependent Hyperadrenocorticism in Dogs and Cats 57

Test Results In dogs with PDH, ultrasonography reveals ● The posterior pituitary gland’s blood supply is direct
VetBooks.ir normal‐sized or enlarged adrenal glands that are typi­ ● The anterior pituitary gland’s blood supply is mainly
(arterial).
cally symmetric; however, mild asymmetry may occur. In
indirect via the pituitary portal system.
dogs with ATs, ultrasonography reveals moderate asym­
metry, contralateral adrenocortical atrophy (adrenal In dogs with normal pituitary glands, after IV adminis­
width <4–5 mm), destruction of normal tissue architec­ tration of contrast medium, the posterior pituitary gland
ture, or some combination of these findings. can be identified first – this phase is called the “pituitary
Ultrasonography can also estimate AT size and possibly
vascular or local soft tissue invasion. Although most ATs flush.” Its absence indicates atrophy due to compression
by a pituitary tumor. Displacement or distortion of the
are unilateral, bilateral tumors may occur and in these flush can be used to identify and localize anterior pitui­
patients, endogenous ACTH concentrations should be tary microtumors.
determined.
Dorsal displacement and decreased signal intensity of
the posterior lobe on T1‐weighted MRI indicate the
Metastasis When an AT has been confirmed, certain tho­ presence of a microtumor.
racic and ultrasonographic findings suggest malignancy.

Adrenal gland width >4 cm.
●
Invasion into the vena cava or adjacent tissues. Treatment
●
However, computed tomography (CT) and magnetic In humans, while pituitary surgery is considered the first
resonance imaging (MRI) are more sensitive techniques line of treatment for patients with Cushing disease, med­
to identify vascular invasion and detect metastases. ical therapy now plays a more important role in the
Adrenalectomy should not be performed without con­ armamentarium available to patients after failed surgery.
firming the presence of an AT (and atrophy of contralat­ Repeat surgery, bilateral adrenalectomy, and pituitary
eral adrenal gland) by abdominal ultrasonography, CT, radiation are also frequently employed.
MRI, or some combination of these. Metastasis can be In dogs, medical management is far more common
confirmed by ultrasound‐guided biopsy, but differentiat­ than surgical approaches and generally involves the use
ing benign from malignant AT often is difficult, even of medications directed toward reducing adrenal gluco­
with histopathologic examination. corticoid production. However, recent work on newer
medical and surgical therapies as well as work on emerg­
Pituitary Imaging ing treatments provides the clinician with multiple ther­
Pituitary imaging provides valuable information regard­ apeutic options.
ing treatment options and prognosis. Pituitary lesions Medical treatments can be classified based on their
range from microscopic nests of hyperplastic cells to mechanism of action and categorized as (1) adrenal‐
large tumors. Absence of neurologic abnormalities does directed steroidogenesis inhibitors or adrenolytics, (2)
not exclude pituitary macrotumors (i.e., tumors that are centrally acting agents, and (3) glucocorticoid receptor
>1 cm in diameter, extend above the sella turcica, or have blockers (Box 7.5).
a pituitary:brain ratio of >0.31).
Adrenal‐Directed Therapies
Indications Pituitary imaging should be considered for In dogs, op‐DDD (mitotane, Lysodren®; Bristol Pharma­
all dogs at the time of PDH diagnosis, especially if hypo­ ceuticals), trilostane (Vetoryl®; Dechra Pharmaceuticals)
physectomy or radiation therapy is being considered. If and ketoconazole are the most commonly used agents
clinical features suggest a pituitary macrotumor, confir­ although several other agents have been used or are
mation requires imaging. Clinical signs of a macroade­ under investigation. In cats, mitotane and trilostane are
noma include disorientation, aimless wandering, severe most commonly used.
polyuria/polydipsia, lethargy, hyporexia to anorexia, vis­
ual impairment and possibly seizures.
Mitotane
Mitotane is derived from the insecticide DDT and is a
Test Results Because pituitary lesions may be quite potent adrenocorticolytic agent. The drug causes pro­
small, contrast‐enhanced CT and MRI may identify nor­ gressive necrosis of the zona fasciculata and zona retic­
mal‐sized pituitary glands in dogs with PDH. However, ularis of the adrenal gland and at higher doses may also
dynamic contrast‐enhanced CT takes advantage of the cause necrosis of the zona glomerulosa. Other effects
pituitary gland’s blood supply. of mitotane include fatty degeneration, centrilobular