In this lecture we will be discussing common abnormalities of the adrenal glands.
Let's first review the location and appearance of the adrenal glands on a normal CT.
So as you recall they are upside down "Y" shaped structures,
that are located just anterior and superior to the kidneys.
You can see them both pointed out here
and you can see the kidneys on both sides right here,
just as adjacent to the adrenal gland anteriorly is the inferior vena cava
and then a portion of the liver on the right.
So the two most common adrenal abnormalities or an adrenal adenoma
which is a lipid field structure and you can see a pathological specimen here.
It appears very homogeneous and appears to be full of fat.
Metastases are the second most common abnormality
and these as you can see on these pathologic specimens
are actually very heterogeneous appearing.
So adrenal adenomas are usually asymptomatic,
they're seen as low-density adrenal masses
and they're most commonly an incidentaloma
or an incidental finding seen on a CT that's performed for another reason.
They contain intracytoplasmic lipid
and they must be differentiated from a metastasis
or pheochromocytoma because the latter two will need treatment
while in adrenal adenoma doesn't need any further follow-up or treatment.
So there are certain specific imaging criteria for adrenal adenomas.
On a non-contrast-enhanced CT they must measure
less than 10 Hounsfield units. If you have an MRI
then they have to show significant loss of signal on the out of phase MRI,
So if you remember when you compare in phase and out of phase MRI
things that contain lipid will lose signal on the out of phase MRI.
However, you can also have what's called a lipid poor adrenal adenoma.
So if their lipid poor then they won't meet the above criteria
and in this situation you have to perform a multiphasic
or adrenal protocol CT. So this is an initial contrast enhanced scan
and it's followed by a delayed scan that's performed
at about 10 to 15 minutes, and then based on this
you can calculate the relative percentage washout from the lesion.
So this is an example of the formula that we use.
The information that you would need are the Hounsfield units of the lesion
on the enhance study, and the Hounsfield units of the lesion
on the delayed study and you can plug these into the formula.
So the relative percentage washout refers to the amount of contrast
that washes out of the lesion on the delayed phase imaging
when compared with the enhanced imaging.
If the RPW is greater than about 40%
then the lesion is considered a benign adenoma.
So let's take a look at this axial CT image.
You can see that the patient has bilateral masses within the adrenal glands.
So on this we don't actually have the Hounsfield unit measurements,
but just taking a look at this image
you can see that the lesions appear low density.
So if you compare with the density of the liver
and you compare with the density of the spleen,
the lesions are lower in density, indicating that they likely contain fat.
So this are actually incidental bilateral adrenal adenomas
that we found on this non-contrast CT.
When we did the Hounsfield unit measurements
the right measures zero and the left measures negative five.
So this fits one of the criteria of a lipid rich adrenal adenoma.
This patient doesn't need any further treatment
or any further follow-up, these are just benign incidental findings.
So the, an adrenal metastases is the most common malignant mass
of the adrenal gland. Metastases can come from the lung, breast, GI tract,
melanoma, kidney and thyroid most commonly.
So adrenal metastases are usually larger than adenomas,
their density is most often greater than 10 Hounsfield units.
Although, occasionally they can present with areas of necrosis
that measure lower Hounsfield units.
The key feature though is that on post contrast imaging
they demonstrate very heterogeneous enhancement,
rather than the homogeneous enhancement that you would see
of an adrenal adenoma. Also, they often demonstrate delayed washout
so with an adrenal adenoma, we have greater than 40% washout
on the delayed phase imaging,
while with an adrenal metastases you wouldn't have that much
the washout would be even later than the delayed phase imaging.
Adrenal metastases usually are T1 hypointense and T2 hyperintense on MRI.
So these are also best evaluated on a multiphasic or adrenal protocols CT.
So usually we start off with a non-contrast study,
and then we have a standard portal venous phase,
and then 10 to 15-minute delayed phase.
So let's take a look at an example, this is a non-contrast CT image
through the level of the adrenal glands,
we then have a portal venous phase image,
and we have a 10-minute delayed image.
So a standard adrenal phase CT
and you can see on the non-contrast images
it appears somewhat hypodense, the lesion then becomes
heterogeneous on the portal venous phase
and remains equally heterogeneous on the delayed phase.
So it demonstrated about 33 Hounsfield units on the non-contrast CT,
which doesn't qualify for the characteristics of adrenal adenoma.
On the enhancement phases we have heterogeneous enhancement
which persists on the delayed phase imaging.
So it doesn't meet the criteria for relative percentage
washout of an adenoma.
This was actually biopsied under CT guidance
and it was found to be metastatic renal cell carcinoma.
So in this lecture we've talked about the differences
between an adrenal adenoma and adrenal metastases,
which are the two most common lesions
that are found within the adrenal gland
and we've also come up with certain characteristics
that will help you differentiate between the two.