Radiopharmaceutical Layering at Posterior Bladder on 18F-FDG PET/CT Imaging

ABSTRACT
Aim: 18F-fluorodeoxyglucose (18F-FDG) is a radioactive agent used to show the metabolic characterization of lesions in positron emission tomography / computed tomography (PET / CT) imaging. The majority of 18F-FDG administered intravenously (IV) is excreted through the kidneys and accumulates diffusely in the bladder. However, it rarely shows layering in the posterior part of the bladder. Our study investigates why 18F-FDG is more layered in the posterior part of the bladder to determine the common characteristics of the patients with this finding and the clinical importance of this situation.
Materials and Methods: As of September 1, 2017, images of 500 consecutive patients who had 18F-FDG PET / CT imaging for various malignancies were examined, and 18F-FDG layers were detected in the bladder 12 patients. Clinical features, laboratory findings, and radiological imaging of these patients were evaluated from the hospital archive.
Results: Layering in the bladder was found in 2.4% of the patients screened. The bladder was observed to be distended in all of these patients. Blood albumin level was found to be below the reference range in 11 patients. Only four patients could obtain a complete urinalysis, and 1 of them had signs of urinary tract infection. This value was high in all nine patients in which we could reach C-reactive protein (CRP) values. Foci showing 18F-FDG uptake consistent with malignancy were observed in all patients. In addition, all patients had Karnofsky Performance scores of 50 or less.
Conclusion: The layering of 18F-FDG observed in the bladder may be related to infection, tumor burden, immobility of the patient, and distended bladder, as well as low blood albumin levels. For this phenomenon to guide clinicians, it should be investigated in more extensive series.
Key words: Urinary bladder, Layering, FDG, PET/CT