DIAGNOSTIC IMAGING
ever an outer hypoechoic rim and hyperechoic inner
zone may be differentiated with progressive imaging
techniques and equipment. This distinction represents
the outer cortex and inner medulla.2 (Figure 1 C)
Feline adrenal glands are typically more oval bilaterally
and homogeneously hypoechoic. It is rare to see the
cortico-medullary distinction in a cat. Mineralisation of
the adrenal glands is common in cats, occurring in up
to 50% of the population.2 Such glands are hyperechoic
with a distal acoustic shadow. This change does not
however affect the size of the gland. Contrary, mineralisation in canine adrenal glands has a high probability of
representing malignant change although rarely, it may
be due to dystrophic change. 1,2,3 (Figure 3)
nodular hyperplasia. In these cases it may be difficult
to distinguish the enlarged hyperplastic gland from an
adrenocortical adenoma. 1,2 (Figure 2)
Another aetiopathogenesis for bilateral adrenomegaly
is trilostane therapy.2,3 This is due to cortical hypertrophy secondary to reduced cortisol production and the
diminished negative feedback mechanism. Following
trilostane treatment, the glands can also become heter-
The cut-off for maximum adrenal gland size in the
dog has been commonly referenced as 0.74mm1,2,4
for either the cranial or caudal pole in either a sagittal
or transverse plane regardless of body weight of the
patient. However a more recent study (n=45), it was
found that the size of the adrenal gland in patients without clinical evidence of hyperadrenocorticism varied
with three weight categories4. The guidelines from this
study are as follows:
Maximum thickness of the caudal pole of the adrenal
gland in sagittal plane:
• Dogs ≤10 kg: ≤0.54cm
• Dogs 10-30kg: ≤0.68cm
• Dogs ≥ 30kg: ≤0.80cm
However the authors do acknowledge limitations to
the study, such as the low study numbers and the need
to further investigate at risk populations of dogs in order to fine-tun H \