Physiological Intraluminal Uptake of ¹⁸F FDG in Gallbladder on PET/CT - A Retrospective Cohort study in North India

¹⁸F fluoro 2-deoxy-D-glucose (FDG) uptake in positron emission tomography/computed tomography (PET/CT) scans is commonly observed in the brain, myocardium, liver, intestines, and excretory pathways such as kidneys and the urinary bladder. This study examines the incidence and contributing factors for physiological FDG accumulation in the gallbladder (GB) lumen, in the absence of clinical history or anatomical abnormalities.

This retrospective study was conducted at a North Indian tertiary care hospital on patients who underwent ¹⁸F FDG PET/CT between January and August 2024. The study group included individuals with GB intraluminal FDG uptake exceeding blood pool levels without anatomical changes, while the control group comprised patients without GB uptake. Comparisons were made based on body mass index, fasting blood sugar, FDG dose, time-to-scan interval, and SUVmax (standardized uptake value). Mann-Whitney U-test was employed for statistical analysis.

Among 632 screened patients, 82 (13%) exhibited GB FDG uptake, whereas 149 were randomly selected for the control group. The study group showed significantly higher fasting blood sugar (101 [24] vs. 93 [18] mg/dl, P = 0.007), FDG dose (6.8 [2.5] vs. 6 [2.3] mCi, P < 0.001), and longer time to scan (82 [54] vs. 78 [38] min, P = 0.02). The median SUVmax for GB uptake was 2.1 (0.93) g/ml.

Physiological GB FDG uptake occurs in about 13% of patients. Increased fasting blood sugar, higher FDG dose, and prolonged scan intervals elevate the likelihood of GB uptake.