Pheo imaging: now you see it, now you don't

Today I will go over some intricacies of pheo imaging. The post is suggested by readers and I will answer some particular questions they have.

For most patients with real pheo, finding the tumor is rather straightforward. Most pheos are about 4-6 cm in diameter and have unique features. CT or MRI describes pheo well. An MIBG scan is then done to see whether there are other pheos lurking in the dark somewhere in the body. Unfortunately for some patients with real pheo and for a lot of patients who do not really have a pheo, imaging can be confusing.

First, for Peep, let's discuss how radiologists make a diagnosis. I work closely with quite a few great radiologists and begin to know their mindset. Radiologists are great at seeing things most other doctors don't see. But they will never be completely sure what the things are because many things can appear the same way. They need clinical information to make a judgment. So Peep, when your urine test results were very high, they will search your body from neck to pelvis trying to find something that might be pheo. A lymph node, or an uncommon normal variation of the shape of a normal organ, can be interpreted as potential pheo. Now the urine results are normal, radiologists will think you probably don't have pheo and take the same findings as what they normally are: lymph node or normal variations. So the same radiological finding in two patients can be read by radiologists as two different diseases. Think this way, the same red liquid in a fancy glass in an expensive restaurant probably is some great wine, while it must be melt lollipop if you see it on the pavement with a stick in the middle. Therefore, Peep, you may have some structures that are not exactly common but can be normal. What they are depends on the risk of your really having a pheo.

Second, for Dennis, let's discuss about MIBG scan. This is the single most misinterpreted imaging for pheo. MIBG scan itself is a great test. It is just some doctors do not know what to make of it. Technically, as Dennis points out, there is an I-131 MIBG, and there is an I-123 MIBG. In a nutshell, don't use the I-131 MIBG for diagnosis (it is used for treatment of pheo). Only use the I-123 MIBG which has a much better signal/background ratio. I-123 just gives much sharper pictures. Second, MIBG scan does not diagnose anyone with pheo, it just shows where the pheo is. As I discussed in a comment before, normal folks often have one adrenal taking more MIBG than the other but they don't have pheo. Nuclear medicine doctors, like radiologists (and any other doctors), will try to find a pheo if they are told there is really a pheo in a patient. If you use photoshop, Dennis, you will know that you can find something you like by adjusting the threshold, the contrast, or the color. If they know the patient has low risk, they will think a little spot might be just a fluke.

The key thing is communication between the endocrinologist and the radiologist. I used to routinely discuss with radiologists on every single case. Now that I know a little about pheo imaging, I still read every patient's images and I will call the radiologists when I feel something is not right. A pheo specialist should be a mini-radiologist on the adrenal gland, at least. My radiologist friends will call me as well if they feel something is not right.

Back to Dennis' point, the most likely place where endocrinologists and radiologists communicate to each other is an academic center with experience on pheo.

Dr. Pheo