Tracking Wall Characteristics of Necrotic Pancreatic Fluid Collections in Acute Pancreatitis on Serial Contrast-Enhanced Computed Tomography

Abstract

Background Encapsulated pancreatic fluid collection (PFC) is a requisite for endoscopic drainage procedures. The 4-week threshold for defining walled-off necrosis does not capture the dynamic process of encapsulation. We aim to investigate the changes in the wall characteristics of PFC in acute necrotizing pancreatitis (ANP) by comparing baseline contrast-enhanced computed tomography (CECT) with follow-up CT scans. Methods This retrospective study comprised consecutive patients with ANP who underwent a baseline CECT within first 2 weeks and follow-up CECT in the third to fifth weeks of illness. Presence, extent, and encapsulation thickness (defined as enhancing wall around the collection) on baseline CECT were compared with follow-up CT (done in the third–fifth weeks of illness). Results Thirty patients (19 males and 11 females; mean age 41.5 ± 13.5 years) were included in the study. The mean time to first CECT was 10 ± 3.6 days. There were 58 collections. The most common site was the lesser sac (n = 29), followed by the left pararenal space (n = 15). At baseline CT, 52 (89.7%) collections had varying degree of encapsulation (15.3%, complete encapsulation). Complete encapsulation was seen in 52 and 82.6% collections in third and fourth week, respectively. All collections in fifth week and beyond were encapsulated. The wall was thicker on follow-up CECT scans (p < 0.01). The mean wall thickness was not significantly associated with the degree of encapsulation (p = 0.417). There was no significant association between the site and degree of encapsulation (p = 0.546). Conclusion Encapsulation is dynamic and collections may get “walled off” before 4 weeks. Walled-off collections should be defined based on imaging rather than a fixed 4-week revised Atlanta classification threshold.