Solid pseudopapillary tumour should be part of differential diagnosis of focal pancreatic lesions with increased 18 F-FDOPA uptake.

OBJECTIVE: To assess the specificity of increased 18 F-dihydroxyphenylalanine (18 F-FDOPA) uptake in patients who underwent PET/CT for suspicion of isolated pancreatic neuroendocrine tumour (pNET). False-positive results mimicking a pNET have been investigated. MATERIAL AND METHODS: Carbidopa-assisted 18 F-FDOPA PET/CT scans performed in patients with suspicion of localized pNET were retrieved. Only patients with a definitive diagnosis were retrospectively included. When available, the histopathological result after pancreatic surgery was the gold standard. In other cases, the diagnosis was based on endoscopic ultrasonography (EUS)/cytology and/or on concordant imaging results of at least two of the following: contrast-enhanced computed tomography (CE-CT), magnetic resonance imaging (MRI) and somatostatin receptor scintigraphy (SRS). RESULTS: Forty-four among 731 patients were selected. Among these, 36 patients (82%) were surgically treated, revealing pNET (n = 28), solid pseudopapillary tumour (SPT) (n = 4), adenocarcinoma (n = 2), serous cystadenomas (n = 1) and solitary fibrous tumour (n = 1) cases. An additional three cases of pNET were diagnosed by EUS/cytology. In the remaining five patients, a consensus was reached on follow-up imaging results: pNET (n = 1), serous cystadenoma (n = 2) and undetermined/no pNET (n = 2). Both specificity and negative predictive value of 18 F-FDOPA PET/CT for localized pNET were 67%. Surprisingly, all four false-positive results were SPTs showing intense 18 F-FDOPA uptake and negative SRS. There was no significant difference in 18 F-FDOPA uptake intensity between PET-positive pNETs and SPTs. CONCLUSION: 18 F-FDOPA PET/CT is not specific for pNET in patients with localized pancreatic lesions. SPT could mimic pNET and should be part of differential diagnosis in such a clinical situation. If these results are confirmed in a broader population, the imaging pattern 18 F-FDOPA PET-positive/SRS-negative lesions might be considered as the imaging phenotype of SPT.