Clinical significance of 18F-FDG PET/CT whole body imaging in detecting incidental abnormalities in cancerous patients

Objective: The aim of this study was to evaluate the significance of incidental abnormalities, including malignant and benign etiology, detected unexpectedly by 18F-fluorodeoxyglucose (FDG) PET/CT whole body (WB) imaging. Methods: The 18F-FDG PET/CT WB imaging performed in 1727 consecutive patients (980 men and 747 women; mean age 63 years) were retrospectively reviewed and followed up for 37 months (mean time 27.5 months). Lesions atypical in location for metastases and unrelated to the primary disease on the PET/CT images were interpreted as incidental abnormalities. These abnormalities were compared with the final diagnosis obtained from pathological confirmation, other imaging modalities diagnosis, and clinical follow-up information. Results: 18F-FDG PET/CT WB imaging suggested incidental benign and malignant lesions in 238(13.8%) of 1727 patients. There were 220 (12.7%) lesions in 213 patients with complete follow-up data. Twenty-two (1.3%) of 1727 patients were pathologically proved to have incidental malignancy or pre-malignancy. Of 60 suspected incidental malignancies, 21.7% (13/60) were proved, including colon-rectal, cervical, lung, left breast, pancreas, stomach, prostate, non- Hodgkin's lymphoma (NHL), abdominal sarcoma, right hilum, and tongue (1 lesion each) tumors, 70.0% (42/60) were false positive. PET/CT also suggested 38 incidental lesions in thyroid (9 pre-malignant or malignant lesions), 26 benign lesions. Of 38 suspected incidental benign mediastinal lesions, 86.8% (33/38) were correctly diagnosed, 7.9% (3/38) were proved to be mediastinal nodal metastasis. Of 84 incidental benign lesions in other regions, 94.0% (79/84) were proved to be true. Conclusions: The total incidental abnormalities were found in 13.8% of WB 18F-FDG PET imaging. Most of the incidental lesions were benign, which could be easily excluded by an experienced reader from unnecessary investigations. The incidental malignancy was found in only 1.3%, and would warrant further investigation and appropriate follow up. (authors)