Posterior bladder layering of excreted 18F-FDG on PET/CT.

ABSTRACT

PURPOSE: This study was carried out to determine the frequency, characteristics and possible causes and clinical significance of occasionally observed posterior layering of excreted 2-deoxy-2-[F]fluoro-D-glucose (F-FDG) in the bladder. PROCEDURES A review of 567 consecutive patients referred for positron emission tomography/computerized tomography studies was performed. Urinary bladder size was measured in patients with and without layering. Urine samples from two patients with layering were imaged ex vivo. RESULTS: Twenty-four of 567 studies (4%) showed F-FDG posterior bladder layering. Mean volume+/-SD of the bladder was 175+/-161 ml in patients with layering and 93+/-83 ml in patients without layering. Urine samples collected from two randomly chosen patients with layering in vivo failed to show layering ex vivo. CONCLUSION: Posterior F-FDG layering occurs in 4% of positron emission tomography/computerized tomography cases and highly correlates with bladder volume. The mechanism is hypothesized to be because of slow F-FDG excretion in patients with a distended urinary bladder resulting in delayed mixing with urine, but needs to be further investigated with a more comprehensive study.