DIAGNOSTIC IMAGING
having one of these tumours, a full metastasis search
should be performed with careful interrogation of the
adrenal glands.
Vascular invasion
Adrenalectomy is the treatment of choice for adrenal
tumours. Regional vascular invasion or tumour thrombus is reported to be as high as 82% for phaeochromocytomas and between 11% to 41% for adrenocortical tumours.3 Vascular invasion has been reported to
occur via the phrenicoabdominal vein with echogenic
material reported in the phrenicoabdominal and renal
veins and the caudal vena cava as a result of extension.1-3
Although vascular invasion is more common with
tumours affecting the right adrenal gland, aggressive
tumours of both glands can invade the caudal vena
cava (Figure 3). Tumour thrombus has been associated with a shorter survival time. A negative finding for
local vascular invasion on ultrasound is however not
sufficient to exclude the possibility and it is advocated that if surgical treatment is intended, a computed
tomography study is performed for optimal surgical
planning.
Figure 3: Markedly enlarged left adrenal gland (A) measuring 4.4
x 2.8cm in dimension and exhibiting heterogeneity and multifocal areas of mineralisation. There was an intraluminal echo
within the caudal vena cava consistent with vascular invasion
(B). This patient also had hyperechoic nodules in the liver which
on fine needle aspirate were consistent with metastatic lesions.
•
change with a benign or malignant lesion more
likely.
Masses ≥ 4.0cm are more likely malignant than
benign.
Besides a diagnoses of adrenocortical tumours, other
tumours occurring in the adrenal glands include myelolipomas, phaeochromocytomas and metastatic
tumours. Benign lesions such as cysts, granulomas
and haematomas can also mimic neoplastic change
in the adrenal glands.1,2
Myelolipomas are benign, endocrinologically inactive
tumours. Their fatty component results in them been
hyperechoic on ultrasound. 2
Phaeochromocytomas are rare catecholamine secreting tumours. Patients present with vague clinical
signs either due to the secretion of catecholamines
or due to the space occupying lesion in the retroperitoneal space. These tumours are incredibly rare in
feline patients. 1,2,5
Several tumours metastasise to the adrenal glands;
mammary, prostatic, gastric and pancreatic carcinomas, squamous cell carcinomas, transitional cell
carcinomas, malignant histiocytosis, melanomas and
haemangiosarcomas.1 Thus if a patient is suspected of
Adrenal gland atrophy
If a patient is suspected of having hypoadrenocorticism, then a finding of small adrenal glands or the inability to find the adrenal glands supports this diagnosis. A cut-off value has been documented as ≤3.0mm
thickness for the left adrenal gland and ≤3.4mm for the
right adrenal gland. However, once again, ultrasound
alone cannot be used to make a diagnosis of adrenal
gland atrophy.1 Other causes for non-visualisation of
the adrenal glands include incorrect transducer selection/ultrasound technique, poor image quality due to
gas in the GIT or patient panting and exogenous steroid administration.2
Conclusion
Ultrasound is the preferred first choice modality for
adrenal gland assessment in patients with suspected pathology. However, there is a certain degree
of overlap in the ultrasonographic appearance of
healthy and diseased glands as well as non-specific
pathological changes making a definitive diagnosis
bases on ultrasonographic findings alone impossible.
It is therefore imperative to correlate ultrasonographic
findings with clinical signs and any clinic-pathological
test results in order to make a definitive diagnosis. In
many cases of adrenal tumours, HY