Ureters (“Beware the Ureter!”)

Because FDG is eliminated via the kidneys, marked metabolic activity fills the renal collecting systems and ureters.  For the inexperienced PET/CT reader, this presents two common problems:

Over-Calling Hypronephrosis & Hydroureter

The normal, yet extremely intense FDG uptake can be mistaken for a degree of hydronephrosis and/or hydroureter. Do not be misled by this normal intense uptake – and only call obstruction when it is confirmed on the co-registered CT images.

Normal collecting systems & ureters.

Malignant Lymph Node vs. Ureter

A second diagnostic challenge for the novice PET/CT reader arises from the fact that ureteral peristalsis commonly results in very asymmetric uptake of FDG within the bilateral ureters at any given level.

And because the intense FDG in a ureter appears much larger than the actual ureter, it is easy to mistake normal ureteral activity for a malignant lymph node.

 Normal intense FDG uptake in a normal-sized ureter.

The Rule

If a focus of intense FDG uptake occurs anywhere along the expected course of the ureter, carefully follow the ureter on the co-registered CT images to assure yourself that the uptake does not simply represent normal ureteral uptake.

On occasion, even after attempting to carefully follow the ureter on the axial non-contrast CT images, it may be necessary to recommend a contrast-enhanced study to differentiate the normal ureter from a possible small malignant node.