Analysis of 18F-FDG PET/CT imaging characteristics in 36 patients with autoimmune pancreatitis

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Objective To investigate the imaging characteristics and the clinical value of 18F-FDG PET/CT imaging in autoimmune pancreatitis (AIP). Methods The 18F-FDG PET/CT imaging characteristics of 36 patients (33 males, 3 females; average age 60 years) with AIP proved by histopathology or clinical follow-up from August 2010 to March 2014 were retrospectively analyzed. The morphologic and metabolic abnormalities of pancreatic and extra-pancreatic lesions were analyzed. The early SUVmax and delayed SUVmax were compared by paired t test in 32 patients who underwent dual time point 18F-FDG PET/CT imaging. Results (1)18F-FDG PET/CT showed diffuse uptake of FDG by the pancreas in 17 patients (47.2%, 17/36), localized uptake in 10 patients (27.8%, 10/36), mixed uptake in 7 patients (19.4%, 7/36), and multifocal uptake in 2 patients (5.6%, 2/36). A total of 33 patients (91.7%) had intense FDG uptake in the pancreas with SUVmax of 5.32±1.83, while the others showed mild FDG uptake with SUVmax of 2.13±0.15. Delayed SUVmax was significantly different from early SUVmax (6.11±2.68 vs 5.08±2.03, t=-7.305, P<0.01) in the 32 patients undergoing delayed scan. The average retention index (RI) in those patients were (18.0±16.1)%. (2) Capsule-like rim surrounding the pancreas was found in 10 patients and abnormality of the main pancreatic duct was found in 9 patients. (3) Thirty-four (94.4%, 34/36) patients had extra-pancreatic lesions, including mediastinal and pulmonary hilar lymph nodes, salivary glands, cervical and submandibular lymph nodes, and foci with the invertedVshaped high FDG uptake in the prostate, which were found in 21 of 33 (63.6%) male patients. (4) The case-times of extra-pancreatic organs involved were 4.17±2.15 in the whole pancreas involved group (diffuse uptake + mixed uptake), and 2.64±1.63 in the partial pancreas involved group (localized uptake + multifocal uptake), which were significantly different (t=2.10, P<0.05). Conclusions Various intense uptake of FDG, which is higher on delayed scan, can be shown in the pancreas in patients with AIP. 18F-FDG PET/CT is an effective modality to detect extra-pancreatic lesions, and it could contribute to the diagnosis and evaluation of AIP. Key words: Autoimmune diseases; Pancreatitis; Tomography, emission-computed; Tomography, X-ray computed; Deoxyglucose