Abstract
1585
Objectives: 18F-Fluciclovine PET/CT scan reading criteria defines lesions as suspicious when the tracer uptake is visually equal to or greater than bone marrow (usually at L3). However, due to PET partial volume effect, lesions < 1 cm (largest axis) are considered suspicious if the uptake is significantly higher than blood pool and approaching bone marrow. Decreasing the threshold for smaller lesions may result in lower specificity. Morphologically, celiac ganglia may appear as a retroperitoneal lymph node (LN). Also, fluciclovine uptake in the catecholamine tissue such as the adrenal glands is variable. 68Ga -PSMA-ligand PET tracer activity in celiac ganglia is intense and can mimic metastatic retroperitoneal LN (EJNM Mol Imaging (2015) 42:210-214). The goal of this study is to characterize the uptake of fluciclovine in celiac ganglia and evaluate whether fluciclovine uptake can potentially mimic metastatic prostate cancer.
Methods: We retrospectively evaluated 159 fluciclovine PET/CT scans performed at our institution between August 2016 and November 2017. For each CT scan, we evaluated the presence of celiac ganglia along the aorta just below the level of the celiac artery. Subsequently, each PET scan was evaluated for focal uptake within the ganglia by visualization. For each visualized ganglion (CT and PET), side (right and/or left), size, and SUVmax were recorded. The ratios of ganglia SUVmax to SUVmean of the L3 marrow (G/M) and blood pool at the aortic bifurcation (G/B) were also recorded. Analysis of uptake in ganglia above and below 1 cm was performed as well. Using STATA software, a T-test statistical exam was performed. A P-value of < 0.05 was considered statistically significant.
Results: The ganglia were visualized on CT in 97% (154/159) of patients. Bilateral ganglia were seen in 91.6 % (141/154) and unilateral ganglion in 8.4% (13/154) of patients. Single left and right ganglia were noted in 9 and 4 patients, respectively. Total of 295 ganglia were recorded with average (±SD) SUVmax of 2.1 (±0.5), G/M of 0.6 (±0.2), and G/B of 1.3 (±0.3). No significant differences were found for fluciclovine SUVmax and ganglia to background ratios between ganglia ≥ 1 cm (n= 204) and ganglia < 1cm (n=91), P>0.05. Visually, only 45/295 ganglia demonstrated focal increased uptake, with higher SUVmax of 2.4 (±0.5), compared with 2.0 (±0.5) for the ganglia with no visualized focal uptake (n=250), p<0.00001. For ganglia ≥ 1 cm (n=39/45), the SUVmax, G/M and G/B were 2.5 (±0.5), 0.7 (±0.2), and 1.5 (±0.3), respectively. These values will not meet the threshold for positive criteria. However, for ganglia < 1 cm (n=6/45), the SUVmax, G/M and G/B were 2.4 (±0.4), 0.6 (±0.1), and 1.5 (±0.3), respectively. These values may reach the threshold for positive criteria.
Conclusions: Overall fluciclovine uptake level within the celiac ganglia does not meet the PET criteria for positive lesions. However, in a small subpopulation of patients with visualized focal uptake in ganglia less than 1 cm, the ganglia may be misinterpreted as prostate cancer with metastatic retroperitoneal LN.