Detection of regional lymph metastasis with 18F-FDG PET/CT imaging in patients with rectal cancer

Abstract

Objective To evaluate the diagnostic value of 18F-FDG PET/CT imaging in detection of regional lymph node metastasis in patients with rectal cancer. Methods A total of 48 patients (37 males, 11 females; average age 59.7 years) with rectal cancer who underwent preoperative PET/CT examination from May 2013 to May 2015 were enrolled. The long diameter, short diameter and SUVmax of lymph nodes on axial images were recorded. Metastatic lymph nodes (MLN) and non-metastatic lymph nodes (NMLN) were confirmed by postoperative pathology. Two-sample t test was used to compare the diameters and SUVmax between 2 groups; ROC curve was drawn to determine the optimal cutoff value and to assess the sensitivity, specificity, and accuracy of each index for differentiating MLN from NMLN. Results A total of 739 lymph nodes were resected, 204 lymph nodes (88 MLN and 116 NMLN) were matched with those on PET/CT images. The long diameters of NMLN and MLN were (6.13±1.94) mm and (8.49±3.78) mm, respectively, and the short diameters were (4.73±1.51) mm and (6.37±2.57) mm, respectively(t=-5.788, -5.691, both P<0.01). The SUVmax of NMLN and MLN were 1.13±0.74 and 2.54±1.76, respectively(t= -7.775, P<0.01). For long diameter, short diameter and SUVmax, the ROC AUCs were 0.709, 0.731 and 0.851 respectively, the optimal cutoff values were 7.50 mm, 5.05 mm and 1.45 respectively, with the corresponding sensitivities of 54.5%(48/88), 67.0%(59/88)and 68.2%(60/88), specificities of 86.2%(100/116), 85.3%(99/116)and 87.9%(102/116), accuracies of 72.5%(148/204), 77.5%(158/204)and 79.4%(162/204). When a lymph node with SUVmax≥1.45 or short diameter≥5.05 mm was considered malignant, the sensitivity, specificity and accuracy were 84.1%(74/88), 83.6%(97/116)and 83.8%(171/204), respectively. Conclusions 18F-FDG PET/CT imaging has significant value in detection of regional lymph node metastasis in patients with rectal cancer. The SUVmax≥1.45 showed better diagnostic value than short diameter≥5.05 mm and long diameter≥7.50 mm. The highest diagnostic accuracy could be achieved, if SUVmax≥1.45 or short diameter≥5.05 mm is considered as the diagnostic criterion for lymph node metastasis. Key words: Rectal neoplasms; Neoplasm metastasis; Lymph nodes; Positron-emission tomography; Tomography, X-ray computed; Deoxyglucose