Imaging of acute necrotic collection and walled-off necrosis complicating acute pancreatitis

Objective: To investigate CT/MRI features of acute necrotic collection (ANC) and walled-off necrosis (WON) complicating acute pancreatitis. Methods: The clinical records of 40 patients (28 men, 12 women, mean age: 50.9 ± 12.2 years) with first-onset acute pancreatitis complicated by ANC (3) or WON (37) from January 2010 to January 2016 were retrospectively analyzed using the 2012 revised Atlanta consensus criteria. Infectious pancreatic necrosis was confirmed by surgery and pus culture. CT or MRI performed 3 to 10 days after onset of acute pancreatitis as well as preoperative and post-operative CT or MRI were reviewed for the site, number, shape, size, CT density, MR signal intensity, enhancement pattern, and severity index. Results: The average time of infectious pancreatic necrosis was 38.4 ± 20.9 days from the onset of acute pancreatitis. The CT/MR severity index was 7.8 ± 1.7 (6-10) in all patients. The size of 44 WON lesions in 37 patients was 8.7 ± 3.6 cm with non-liquid densities/signal intensities. 'The bubble sign' and/or 'gas fluid level sign' were seen in 56.8% of infectious WON lesions on MRI or CT. The spleen was involved with pancreatic tail WON in 13.5% showing rimor septal enhancement. 67.5% of patients had mixed organisms on bacterial culture. Conclusion: Infectious ANC or WON has MRI and CT features that aid diagnosis and treatment planning. (authors)