Something new for adrenal nodules

Those of us in body imaging are constantly barraged by incidental findings, which we feel we must do something about. One common finding on the routine contrast-enhanced CT is the adrenal nodule, which can lead to an extensive workup, when vast majority are benign adenomas, and of no consequence. Workup includes imaging to establish benignity, typically with an adrenal protocol CT or MRI.

Benign adenomas have 2 properties on imaging: low density on non-contrast (due to abundant fat) maximal enhancement in portal venous phase followed by rapid washout.

We know that we can use virtual non-contrast (VNC) on routine contrast enhanced CT to establish low density, but this ends up being low sensitivity, as subtraction of iodine is not perfect, and nodules end up having higher density than true non-contrast.

In a recent paper, Dr. Nagayama and colleagues from Japan describe a new method to look at these nodules, the iodine density to VNC ratio. Simply stated, adenomas have a high iodine content, therefore ratio of iodine concentration to VNC attenuation can more accurately classify these nodules as benign.

Here is an example: 65 yo M with abdominal pain has a 2.1 cm adrenal nodule, measures about 130 HU. On VNC the density is 34 HU, so the lesion would be indeterminate.

The iodine density is 4 mg/mL. Using Dr. Nagayama’s method, we multiply iodine density x 100, and divide by attenuation on VNC. In this case that would be 400/34, about 11.8. Using a cutoff of 6.7, this ratio is 95% sensitive and specific for adenoma. The nodule in this case is way above the cutoff.

We found an outside CT from 20 years prior: The nodule was unchanged, proving benignity!

I believe this is a very innovative method to look at these nodules, please read the paper, you will be impressed as well.

Conventional CT: The nodule warrants workup.

Virtual non-contrast: Attenuation not low enough to let go

Iodine density: Shows intense iodine uptake. We can calculate ratio of uptake to VNC attenuation. Here the ratio is definitely diagnostic of a benign adenoma.

CT from 20 years prior: The proof is in the pudding!