Autoimmune pancreatitis: An incidental detection on FDG PET/CT with response to steroid therapy
A 72-year-old gentleman, a diagnosed case of small cell lung cancer stage IIIA, was referred for a whole body 18F-FDG PET/CT study, for pre-treatment staging. Patient was breathless, but had no abdominal complaints. Maximum intensity projection (MIP) image showed intense mediastinal tracer concentration at the site of primary [-arrow]; however also seen was moderately increased tracer uptake in the mid-abdomen [-arrow head]. On axial CT [-arrow] and PET/CT [-arrow] image, a large enhancing FDG avid mediastinal mass was seen, predominantly to the right, encasing the right main bronchus and causing vascular compression. Also, PET/CT image showed diffusely increased tracer uptake in the pancreas [-arrow]. Axial contrast enhanced CT image revealed featureless pancreas with diffuse, homogenous, sausage-shaped enlargement, with minimal post-contrast enhancement, associated with diffuse narrowing of main pancreatic duct [-arrow]. No focal lesion or mass was noted in the pancreas. No calcification, peripancreatic fluid or perilesional adenopathy was seen. Liver function tests and CA-19.9 levels were normal. Though, patient was asymptomatic, based on the imaging features, a suspicion of AIP was raised. This was confirmed by raised serum lipase and amylase levels, and raised IgG4 titer (230 mg/L, normal value < 135 mg/L). Small cell lung cancer was managed with a chemotherapy regimen of four cycles of cisplatin with etoposide (Cisplatin 60-80 mg/m2 on day 1 and etoposide 80-120 mg/m2 on days 1-3, every 21 days). Oral corticosteroid (prednisolone 40 mg/week for 4 weeks, tapering by 5 mg/week for 12 weeks) was given for AIP and thereafter, a follow-up PET/CT study was performed. MIP image showed a significant reduction in mediastinal tracer uptake [-arrow] suggestive of response to chemotherapy, with no tracer uptake in the mid-abdomen. Axial PET/CT [-arrow] and CT image [-arrow] showed no pancreatic tracer uptake, with restoration of normal size and architecture of pancreas. Also normal levels of serum amylase, lipase, and IgG4 were seen. These findings, in retrospect, confirmed the presence of AIP.