Value of 18-fluorodeoxyglucose positron emission tomography in the management of patients with cystic tumors of the pancreas

Abstract

Objective: To assess the reliability of 18-fluorodeoxyglucose positron emission tomography (18-FDG PET) in distinguishing benign from malignant cystic lesions of the pancreas.

Summary background data: The preoperative differential diagnosis of cystic lesions of the pancreas remains difficult: the most important point is to identify malignant or premalignant cysts that require resection. 18-FDG PET is a new imaging procedure based on the increased glucose metabolism by tumor cells and has been proposed for the diagnosis and staging of pancreatic cancer.

Methods: During a 4-year period, 56 patients with a suspected cystic tumor of the pancreas underwent 18-FDG PET in addition to computed tomography scanning, serum CA 19-9 assay, and in some instances magnetic resonance imaging or endoscopic retrograde cholangiopancreatography. The 18-FDG PET was analyzed visually and semiquantitatively using the standard uptake value. The accuracy of 18-FDG PET and computed tomography was determined for preoperative diagnosis of a malignant cyst.

Results: Seventeen patients had malignant tumors. Sixteen patients (94%) showed 18-FDG uptake with a standard uptake value of 2.6 to 12.0. Twelve patients (70%) were correctly identified as having malignancy by computed tomography, CA 19-9 assay, or both. Thirty-nine patients had benign tumors: only one mucinous cystadenoma showed increased 18-FDG uptake (standard uptake value 2.6). Five patients with benign cysts showed computed tomography findings of malignancy. Sensitivity, specificity, and positive and negative predictive values for 18-FDG PET and computed tomography scanning in detecting malignant tumors were 94%, 97%, 94%, and 97% and 65%, 87%, 69%, and 85%, respectively.

Conclusions: 18-FDG PET is more accurate than computed tomography in identifying malignant pancreatic cystic lesions and should be used, in combination with computed tomography and tumor markers assay, in the preoperative evaluation of patients with pancreatic cystic lesions. A positive result on 18-FDG PET strongly suggests malignancy and, therefore, a need for resection; a negative result shows a benign tumor that may be treated with limited resection or, in selected high-risk patients, with biopsy, follow-up, or both.

Figure 1. Positron emission tomography scan shows a focus of increased uptake (standard uptake value 5.0) within the pancreatic cyst (mucinous cystadenocarcinoma of the tail of the pancreas). The normal uptake of the kidneys is marked K. Coronal, transverse, and sagittal reconstructions (left to right).

Figure 2. Positron emission tomography shows focal uptake within the cyst (standard uptake value 3.6; left) and peripheral uptake of the cystic wall (standard uptake value 6.0; right) Papillary/cystic tumor of the body and tail and neuroendocrine tumor of the head of the pancreas, respectively.

Figure 3. (Upper) Computed tomography scan of the abdomen shows marked dilation of the main pancreatic duct with solid papillary projections in this benign intraductal mucin hypersecreting tumor. (Lower) Magnetic resonance imaging of the abdomen shows a large cystic mass with mural nodules in the tail of the pancreas (mucinous cystadenoma).