The differential diagnosis between benign and malignant cystic lesions of the pancreas based on conventional imaging (CT or US-scan, MRI) is still unreliable in a number of patients. Aim of this study was to investigate the usefulness of 18-FDG PET in the differential diagnosis between benign and malignant cystic lesions of the pancreas.
METHODS: In a 4-year period, 56 patients with suspected cystic tumor of the pancreas underwent 18-FDG PET in addition to serum CA 19-9 assay, CTscan, and, in some cases, to MRI or endoscopic retrograde cholangiopancreatography (ERCP). The 18-FDG PET was analyzed visually and semiquantitatively using the Standard Uptake Value (SUV). The accuracy of 18-FDG PET and CT were determined for evaluation of preoperative diagnosis of malignant cyst.
RESULTS: Seventeen patients had a malignant tumor (Mucinous cystic tumor: 8; Adenocarcinoma with cystic degeneration or retention cyst: 5; Endocrine: 2; Solid-cystic tumor: 1; Intraductal papillary mucinous tumor: 1). FDG-PET correctly diagnosed a malignant lesion in 16 patients (94%) with a SUV range from 2.6 to 12.0. Twelve patients (70%) were correctly identified as having malignancy by CT-scan and/or CA 19-9 assay. Thirty-nine patients had benign tumors (Mucinous cystic tumor: 6; Serous cystic tumor: 11; Pseudocyst: 8; Congenital cyst: 2; Intraductal papillary mucinous tumor: 8; Duodenal enterogenous cyst: 1; Mesenteric cyst: 1; Cystic lymphangioma: 1; Endocrine:1). Only one Mucinous cystic tumor showed increased 18-FDG PET uptake (SUV 2.6). Five patients with benign cysts showed CT findings of malignancy. Sensitivity, specificity, positive and negative predictive values of 18-FDG PET and CT-scan in detecting malignant cystic tumors were 94%, 97%, 94%, 97% and 65%, 87%, 69%, 85% respectively.
CONCLUSIONS: 18-FDG PET is more accurate than CT in the identification of malignant pancreatic cystic lesions and should be used, in combination with CT and tumor markers assay, in the evaluation of pancreatic cystic lesions. The positivity of 18-FDG PET strongly suggest malignancy and, therefore, a must of resection. The negativity of 18-FDG PET shows a benign tumor that may be treated with limited resection or, in selected high-risk cases, with biopsy and/or follow-up.