What to look for
In cats, the most common ultrasonographic changes observed with primary hyperaldosteronism include adrenal masses, adrenal
calcification, and changes in adrenal echogenicity (Figure 2).11,12,14,18 In cases of unilateral adrenal masses, the contralateral adrenal gland can appear normal or may not be able to be visualized
ultrasonographically. The median dorsoventral width of the adrenal glands of healthy cats has been reported to be 3.9 mm for
the left (range: 3 to 5.3 mm) and 3.9 mm for the right (range: 2.9 to 4.5 mm).9,22 Results have also shown that parameters of body size, including body weight and surface area, were not significant determinants
of adrenal dimensions in cats, thus allowing for a single reference interval for all cats.22
2. An ultrasonogram of a unilateral adrenal tumor measuring 1.7 x 2 cm. Note the enlarged, rounded hypoechoic appearance
of the adrenal gland with architectural loss.
The observed morphology of normal feline adrenal glands has been described as bean-shaped to ovoid and hypoechoic to the surrounding
tissue.22 In one case series, dorsoventral measurements of ultrasonographically confirmed unilateral adrenal masses ranged from 1
to 3.5 cm, and some showed evidence of compression, close association with the caudal vena cava, or both.12 Finding an enlarged adrenal gland or mass is not definitive for a diagnosis of primary hyperaldosteronism, as other considerations
for these findings include pheochromocytomas, cortisol-secreting tumors, nonfunctional tumors, and progesterone-secreting
Diagnostic imaging has limitations associated with identifying the underlying cause of primary hyperaldosteronism. Functional
tumors and clinically relevant hyperplasia of the zona glomerulosa may not be large enough to be revealed by conventional
diagnostic imaging techniques, and adrenal glands could appear normal. One cat was determined via ultrasonography to have
a right adrenal mass and a normal left adrenal gland, but postmortem examination revealed bilateral adrenocorticol adenomas.12 In another report of 11 cats with histologic confirmation of primary hyperaldosteronism, diagnostic imaging with ultrasonography
revealed absent to minor changes in the size and morphology of the adrenal glands.6 Two of these cats had CT performed in addition to ultrasonography, which also revealed no abnormalities of the adrenal glands,
but nodular hyperplasia was confirmed by histologic examination.6
These cases suggest that primary hyperaldosteronism due to idiopathic bilateral nodular hyperplasia probably occurs more frequently
than is reported and that this disease is not always associated with an adrenal tumor or ultrasonographic abnormalities. Distant
metastatic disease in cases of adrenocorticol adenocarcinomas can be missed if their size is below the detection limit of
the imaging technique, as occurred in one cat in which thoracic radiographs failed to reveal a 3-mm pulmonary metastatic nodule.23
Feline primary hyperaldosteronism has become increasingly recognized and diagnosed in cats, and its prevalence is likely underestimated.
CKD is often thought to be the causal disorder for cases with classic presenting signs, when, in fact, CKD may be a consequence
of primary hyperaldosteronism.
Screening for this disease should be performed in any cat presenting with hypokalemia or hypertension, as well as the subset
of cats presenting with mild azotemia, if preliminary minimum database diagnostics fail to identify other underlying disease
processes. Diagnostic tests should include a complete physical examination, complete blood count, serum chemistry profile,
total T4 measurement, urinalysis, and blood pressure measurement.
If primary hyperaldosteronism is suspected, the plasma aldosterone concentration should be measured and compared with a concurrent
serum potassium concentration. Abdominal ultrasonography can be pursued to attempt to differentiate neoplasia from nodular
hyperplasia and determine the laterality of disease, but the adrenal glands could also appear normal.
In the next article, find out when medical or surgical treatment is recommended and the likely prognosis for affected cats.
Joseph Bisignano, DVM
Department of Veterinary Clinical Sciences
College of Veterinary Medicine
University of Minnesota
St. Paul, MN 55108
David S. Bruyette, DVM, DACVIM VCA
West Los Angeles Animal Hospital
1818 S. Sepulveda Blvd.
Los Angeles, CA 90025
Veterinary Diagnostic Investigation and Consultation
26205 Fairside Road
Malibu, CA 90256