CT and MRI Features and Prognosis of Acute Necrotic Collectionsin Patients with Acute Pancreatitis

Objective: To summarize the imaging features of acute necrotic collections (ANC), a local complication of acute necrotizing pancreatitis (ANP), and to explore the factors affecting the prognosis of patients with ANC. Methods: The clinical and imaging data of 31 patients with ANP were analyzed retrospectively. Characteristics of ANC on computed tomography (CT) and magnetic resonance imaging (MRI) were analyzed as well. Based on the follow-up outcomes, patients were divided into the absorption group and the walled-off necrosis (WON) group; a chi-square test was used to compare the two. Results: Plain CT revealed patchy, uneven, low-density shadows in 31 cases of ANC (focal, oval, and iso-density and low-density mixed shadows:23 cases; fatty low-density shadows: 22 cases). Plain MRI revealed mixed low-signal intensities on T1-weighted imaging and mixed high-signal intensities on T2-weighted imaging in 19 cases of ANC; low-signal fragments were seen on Fat suppressed T2-weighted imaging in some of these cases. ANC was complicated with local infection and hemorrhage in 3 (9.7%) and 12 (38.7%) cases, respectively. The necrotic tissues did not show any enhancement, but the surrounding tissues appeared patchy or linear-enhancing changes with varying degrees on enhanced scans. Follow-up examination (median: 137 days) revealed that ANC was completely absorbed in 12 cases (38.7%) and had developed into WON in 19 cases (61.3%). The absorption and WON groups differed significantly in terms of necrosis involving the pancreas, affected locations of the pancreas, necrotic volumes, and the modified CT severity index scores. Conclusion: On CT and MRI, ANC appears as uneven liquid densities and heterogeneous signal intensities, respectively. The necrotic tissue itself has no enhancement, but its surrounding tissue presents with different degrees of enhancing changes on enhanced scanning. Follow-up findings reveal that ANC can completely dissipate or progress to WON, which is related to several imaging factors.