Clinical significance of incidental, photopenic, high CT density renal lesions on [18F]FDG PET/CT

OBJECTIVES: Incidental renal lesions are commonly detected in [18F]FDG PET/CT studies and there is little evidence on which need further characterisation. This study investigated the negative predictive value associated with definite photopenia in high CT density renal lesions, for ruling out a malignancy. METHODS: Incidental high CT density, completely photopenic, renal lesions identified on [18F]FDG PET/CT studies performed in our institution from 2014 to 2024 were included. Further investigations including imaging and histology results of these lesions were reviewed to ascertain their nature and calculate negative predictive value of photopenia. A list of confirmed renal cell carcinoma lesions from MDT discussion (2015 to 2018) was used to identify whether any of those lesions were photopenic on PET/CT scans performed. RESULTS: 23 out of 24 included renal lesions were shown to be simple or haemorrhagic cysts on further imaging (NPV 96%). None of the proven renal cell carcinomas from MDT discussion were photopenic on [18F]FDG PET/CT. CONCLUSIONS: Photopenia in high density renal lesions on [18F]FDG PET/CT is associated with a high NPV to exclude malignancy. ADVANCES IN KNOWLEDGE: Even though previous studies have investigated the role of PET/CT in renal lesions, this is the first study to explicitly calculate NPV associated with photopenic renal lesions. This can rationalise, and potentially reduce, additional dedicated renal imaging.