Fluorodeoxyglucose uptake in absence of CT abnormality on PET-CT: What is it?

Abstract

The purpose of this article is to provide a pictorial review of the findings and interpretative pitfalls about focal fluorodeoxyglucose (FDG) uptake in the absence of corresponding computer tomography (CT) lesion or abnormality on an integrated positron emission tomography (PET)-CT. The integrated CT images in the PET-CT scanner allow correct co-registration and fused imaging of anatomical and functional data. On FDG PET-CT imaging, a real pathologic process often demonstrates abnormal uptake associated with a visible corresponding CT lesion or abnormality. When focal uptake is seen on PET imaging but no corresponding anatomic abnormality is visualized on the integrated CT, one should always be aware of possible mis-registration or mismatch of the PET and CT images due to the patient’s respiratory or body motion. While most of the hot spots in the absence of corresponding anatomic abnormalities are artefactual or secondary to benign etiologies, some may represent small sized or early staged neoplasm or metastases, especially in the gastrointestinal tract and skeletons. Caution should be exercised to simply diagnose a pathology based on the presence of the uptake only, or exclude the disease based on the absence of anatomic abnormality.

Keywords: Fluorodeoxyglucose uptake; Positron emission tomography-computer tomography; ARTEF actual uptake; Mis-registration; Positron emission tomography interpretation

Core tip: Abnormal focal uptake without corresponding anatomic abnormality on the integrated computer tomography (CT) imaging poses a dilemma in interpretation of whole-body fluorodeoxyglucose positron emission tomography (PET)-CT imaging. Most of the PET hot spots with the absence of CT lesions or abnormalities are artefactual or secondary to benign etiologies, but some may represent early staged or small sized neoplasm or metastases especially in the gastrointestinal tract and skeletons. Caution should be exercised to simply diagnose a pathology based on the presence of the uptake only, or exclude the disease based on the absence of anatomic abnormality.