Extravasation of Injected FDG
FDG is injected intravenously. As many cancer patients have challenging venous access issues, partial extravasation of FDG during injection is not uncommon (an estimated 10% of patients have evidence of extravasation on their PET images).
Extravasation of FDG at the time of the intravenous injection can result in false positive interpretations due to:
- Focal intense uptake at the injection site.
- Linear uptake along the lymphatic channels within the arm (appearing as long vessels).
- Focal uptake in small ipsilateral axillary nodes.
If these nodes are enlarged, be cautious before dismissing them as “injection-related”. We have seen more than one case of a radiologist calling axillary nodes “injection-related”, when the patient was injected in the opposite arm.
When we see any of these above findings, we briefly make note of them in the body of the report:
“Evidence of mild radiopharmaceutical extravasation is noted to involve the left arm and left axilla.”
OR
“Several subcentimeter FDG-avid left axillary nodes are present, felt to be injection-related, as evidence of radiopharmaceutical extravasation is noted in the left antecubital fossa.”
If the volume of extravasation is large enough, it can result in a significant reduction of circulating FDG available for tumoral uptake, resulting in false negative results (“Sponge Effect”, discussed here).
