FDG-PET/CT Is Superior to Enhanced CT in Detecting Recurrent Subcentimeter Lesions in the Abdominopelvic Cavity in Colorectal Cancer

Purpose This study aims to compare the performance of contrast-enhanced computed tomography (CeCT) and 18 F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in detecting small tumor implants and metastatic lymph nodes (LNs) in the abdominopelvic cavity in patients with colorectal cancer. Methods We enrolled 16 patients who were clinically suspected of experiencing a recurrence (6 male, 10 female; mean age 61 ± 14 years). All subjects underwent CeCT and PET/CT, and the performance of these methods was compared with regard to detecting recurrences. The final diagnosis of a recurrence was made clinically. Results CeCT identified 38 lesions in 12 patients, all of which were detected by PET/CT. PET/CT found 27 additional lesions in 8 patients, comprising 9 seeding nodules (2 in the right upper quadrant of the abdomen and 7 in the pelvic cavity) and 18 LNs (2 celiac, 2 paraaortic, 2 hepatic hilar, 11 common iliac, 1 external iliac). Most additional lesions were located in the pelvic cavity (approximately 78% of seeding nodules and 67% of lymph nodes). The maximum standardized uptake value (SUVmax) of the additional seeding nodules that were detected solely by PET/CT was significantly higher compared with the CeCT- and PET/CT-confirmed nodules (5.5 ± 4.2 vs. 2.9 ± 2.5, p = 0.03). The seeding nodules that were detected only by PET/CT were significantly smaller than the CeCT- and PET/CT-confirmed nodules (long axis: 1.0 ± 0.3 cm vs. 2.0 ± 1.1 cm, p = 0.001; short axis: 0.8 ± 0.3 cm vs. 1.4 ± 0.8 cm, p = 0.004; mean of both axes: 0.9 ± 0.3 cm vs. 1.7 ± 0.9 cm, p = 0.001). Similarly, PET/CT-only-detected LNs were significantly smaller than CeCT- and PET/CT-identified LNs (0.7 ± 0.1 cm vs. 2.3 ± 1.2 cm, p