Page 892 - Small Animal Internal Medicine, 6th Edition

864 PART VI Endocrine Disorders

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A B

FIG 50.7
Ultrasound images of the adrenal glands in an 11-year-old male castrated Golden
Retriever with adrenal-dependent hyperadrenocorticism. (A) Cortisol-secreting tumor
affecting the right adrenal gland (arrows). The maximum diameter of the adrenal mass
was 1.6 cm. (B) The left adrenal gland has undergone marked atrophy (arrows and
crosses) as a result of suppression of pituitary adrenocorticotropic hormone secretion after
negative feedback inhibition caused by the adrenocortical tumor. The maximum diameter
of the left adrenal gland was less than 0.2 cm.

tumor (Fig. 50.9). The finding of normal-size adrenal glands
in a dog with confirmed hyperadrenocorticism is most con-
sistent with a diagnosis of PDH. The finding of bilateral
adrenomegaly with the appearance of multiple nodules of
Adrenal mass varying size is suggestive of macronodular hyperplasia
(Fig. 50.10). Bilateral adrenal macronodular hyperplasia is
believed to represent an anatomic variant of PDH. Failure to
identify either adrenal is considered an inconclusive finding,
and ultrasonography should be repeated at a later time.
CVC CT and MRI can be used to evaluate the pituitary gland
for a macroadenoma, to assess the size and symmetry of the
TT adrenal glands, and to detect the presence of an adrenal
tumor thrombus in the adjacent vasculature. Contrast
enhancement using an iodinated contrast agent (CT) or
gadolinium (MRI) given by continuous intravenous (IV)
infusion during the imaging procedure aids in identification
FIG 50.8 of a pituitary macroadenoma and the adrenal glands during
Ultrasound image of a mass affecting the left adrenal gland CT and MRI examination, respectively (see Fig. 50.4). The
(adrenal mass) and extending into the lumen of the caudal
vena cava (CVC), creating a tumor thrombus (TT) in a primary indications for CT or MRI are (1) to confirm the
9-year-old male Standard Poodle. The maximum width of presence of a visible pituitary tumor in a dog with clinical
the adrenal mass was 3.8 cm. The histopathologic signs suggestive of macrotumor (see the section on pituitary
diagnosis was pheochromocytoma. macrotumor syndrome) or in a dog diagnosed with PDH for
which the client is willing to consider pituitary irradiation
or hypophysectomy should a pituitary mass be identified
the mass does not differentiate adenoma from carcinoma. (see the sections on pituitary irradiation and hypophysec-
Generally, the larger the mass, the more likely it is carci- tomy) and (2) to assess the size of an adrenal mass and the
noma. Asymmetry in the size of the adrenal glands is evident extent of infiltration of the mass into surrounding blood
(see Fig. 50.2). Ideally, the contralateral unaffected adrenal vessels, organs, and body wall before adrenalectomy. MRI is
should be small or undetectable (maximum width typically superior to CT for detecting small pituitary tumors; for
< 0.4-0.5 cm) as a result of ADH-induced adrenocortical revealing associated tumor features such as edema, cysts,
atrophy (see Fig. 50.7), although a normal-size contralateral hemorrhage, and necrosis; and for imaging the adrenal
adrenal gland does not rule out ADH. Identification of an glands.
adrenal mass and a normal to large contralateral adrenal
gland in a dog with clinical signs supportive of hyperadre- TESTS OF THE PITUITARY-
nocorticism suggests the possibility of PDH with a concur- ADRENOCORTICAL AXIS
rent adrenal mass that may be a pheochromocytoma, a Clinical signs, physical examination findings, and clinico-
functional adrenocortical tumor, or a nonfunctional adrenal pathologic alterations should provide strong support for