Abnormal fluorodeoxyglucose uptake in lung without structural abnormality on computed tomography

Abstract

Fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) is a useful proven imaging modality in the management of many types of cancers. It is being used at various stages of treatment of cancer. Knowledge regarding the physiological biodistribution and false-positive findings should be kept in mind for correct interpretation. Pulmonary FDG uptake can be due to different causes such as infection, inflammation, and metastases which are invariably associated with structural abnormality on CT. In rare circumstances, there can be a focus of FDG uptake in the lung with no corresponding structural abnormality which might be due to an inflammatory vascular microthrombus or due to iatrogenic microembolism caused during the injection of radiotracer. It is important to be aware of this as it can cause difficulty in interpreting the scan and can lead to false-positive findings. It also highlights the importance of hybrid imaging in the form of PET-CT as there is a definite possibility of misinterpreting this as a site of metastasis in a known carcinoma patient if there was no corresponding CT image.

The hot embolus of 18F-fluorodeoxyglucose

“…The CT portion of the PET-CT is important to the scanning as it enables anatomical localization of lesions showing metabolic activity on PET scan. [ 6 7 8 ]…”

“…Absent metabolic activity in lesions seen on CT may be due to low FDG avidity, treated lesions, small lesions that are sub-centimeter sized that are beyond the resolution of PET scan, or partial-volume effect. [ 7 ]…”

“…The CT portion of the PET-CT is important to the scanning as it enables anatomical localization of lesions showing metabolic activity on PET scan. [6][7][8] The etiology of this "hot clot"/"emboli" has been attributed to a fault in the injection technique of the radiotracer. It occurs due to agglutination of FDG by erythrocytes during FDG injection.…”

“…Absent metabolic activity in lesions seen on CT may be due to low FDG avidity, treated lesions, small lesions that are sub-centimeter sized that are beyond the resolution of PET scan, or partial-volume effect. [7] Other causes of focal metabolic activity on PET images without a CT counterpart have also been given. Mis-registration of PET and CT images is also a reason for mismatch between the findings on these two modalities.…”