Ultrasound and X-ray are both useful tools in detecting neoplasms, but
both rely on showing the outline of a neoplasm, and generally work only
if there is marked enlargement of a normal structure.  However, like any
diagnostic test, it has its limitations.  Because adrenal neoplasms may be
small enough not to cause enlargement of the gland, these may be missed
with both ultrasound and X-ray, and diagnosed only on clinical signs, or
elevated levels of estrogen or its precursors in the blood.
 
Here is a common scenario - ferret presented for clinical signs of
symmetrical baldness.  Ultrasound is scheduled.  Well, as soon as the
clinician walks in and sees the bald ferret - he or she is immediately
geared to seeing an enlarged adrenal gland, and is likely to see one
regardless of what the monitor shows.  It's unavoidable bias, and a test
whose outcome is so predestined, it's not valid.  This is one of the
reasons that I generally recommend going to surgery if the clinical signs
fit the profile, and not waiting for ultrasound to be performed.
 
Ultrasound and x-rays are good tools in the diagnosis of neoplasia, but
only that.  The statement that it always finds the tumor is patently
overstating its significance.
 
With kindest regards,
Bruce Williams, DVM
[Posted in FML issue 3601]