Background: According to the revised Atlanta classification, acute necrotizing pancreatitis (ANP) involves variable degrees of parenchymal and extra-parenchymal necrosis with acute necrotic collections that may develop into walled-off necrosis after four weeks. However, encapsulation—a prerequisite for endoscopic drainage—doesn't strictly adhere to this 4-week threshold. Current guidelines recommend delaying drainage until encapsulation occurs, yet the temporal evolution of this process remains poorly characterized prospectively.
Aim: To evaluate the preliminary results of the temporal evolution of pancreatic fluid collection (PFC) encapsulation using serial axial T2-weighted MRI.
Methodology: This preliminary analysis is part of an ongoing trial (NCT05716633) that began in February 2023. Of the patients with ANP enrolled till December 2024, we screened the data for patients with lesser sac PFCs > 5 centimeters in maximum short axis dimension who underwent at least three serial abbreviated T2-weighted MRIs prior to drainage or demise. The MRI acquisition started from day 14 after the onset of ANP, with follow-up MRI performed every 5 days (last MRI at day 23-25). Two experienced abdominal radiologists independently evaluated lesser sac collections for the collection size, presence of capsule, capsule thickness, degree of encapsulation (<20%,20-50%,50-80%,>80%-clinically significant), and solid debris percentage on each MRI.
Results: Fourteen patients (mean age 32.1±13.2 years; 12 males) were analyzed. Etiology included alcohol (n=7), gallstone disease (n=5), and others (n=2). Thirteen patients had severe disease with organ failure in 10. Mean collection size in short axis was 5.0±1.8 cm on initial MRI, 5.6±1.9 cm on second MRI, and 5.5±2.2 cm on third MRI. Mean capsule thickness increased progressively (2.6±0.5mm, 3.0±0.8mm, and 3.4±0.9mm on consecutive MRIs). While all collections showed encapsulation on 1st MRI, clinically significant encapsulation developed in 6/14 patients (42.9%) by the third MRI. Collections with lower initial debris percentage (<20%) achieved significant encapsulation more frequently (5/7 vs 1/7). High interobserver agreement was observed for all MRI parameters.
Conclusion: These preliminary findings demonstrate that encapsulation is a dynamic process that starts early after onset, and clinically significant encapsulation occurs in almost half of the patients by day 23-35. The complete study results will provide deeper insights into factors affecting encapsulation.