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.

Comparison of Functional Deficit Zone Defined by FDG PET to the Epileptogenic Zones Described in Stereo-Electroencephalograph in Drug-Resistant Epileptic Patients Treated by Surgery.

INTRODUCTION: The purpose of presurgical assessment is to delimit the epileptogenic zone and the functional deficit zone with a brain MRI, an electroencephalograph or even a stereo-electroencephalograph (SEEG), neuropsychological evaluation, and a cerebral FDG PET. Several studies concur that the hypometabolism of FDG PET seems to be consistent with epileptogenic zones. We compared the functional deficit zone defined by FDG PET with the results of the SEEG, for each cluster electrode contact (CEC) located in the gray matter. METHODS: The electrode diagram of the 15 patients (486 CECs) operated on for drug-resistant epilepsy was merged with MRI and FDG PET. The metabolisms of FDG PET and SEEG were compared using a logistic regression test. RESULTS: The presence of hypometabolism resulted in a significantly higher risk of being in the seizure onset zone and the irritative zone, particularly when it was intense. Of the deeply hypometabolic CECs, 47% were in the seizure onset zone and 76% in the irritative zone. Normal metabolism resulted in a significantly higher probability of being in the healthy zone. CONCLUSIONS: This study demonstrated an association between the presence of normal metabolism and the location of CECs in the healthy zone, and between the presence of pathological metabolism and the location of CECs in the seizure onset zone and the irritative zone, with metabolism abnormalities progressively more present and more intense near the seizure onset zone.