Pancreatic fluid collections: What is the ideal imaging technique?

Abstract

Pancreatic fluid collections (PFCs) are seen in up to 50% of cases of acute pancreatitis. The Revised Atlanta classification categorized these collections on the basis of duration of disease and contents, whether liquid alone or a mixture of fluid and necrotic debris. Management of these different types of collections differs because of the variable quantity of debris; while patients with pseudocysts can be drained by straight-forward stent placement, walled-off necrosis requires multi-disciplinary approach. Differentiating these collections on the basis of clinical severity alone is not reliable, so imaging is primarily performed. Contrast-enhanced computed tomography is the commonly used modality for the diagnosis and assessment of proportion of solid contents in PFCs; however with certain limitations such as use of iodinated contrast material especially in renal failure patients and radiation exposure. Magnetic resonance imaging (MRI) performs better than computed tomography (CT) in characterization of pancreatic/peripancreatic fluid collections especially for quantification of solid debris and fat necrosis (seen as fat density globules), and is an alternative in those situations where CT is contraindicated. Also magnetic resonance cholangiopancreatography is highly sensitive for detecting pancreatic duct disruption and choledocholithiasis. Endoscopic ultrasound is an evolving technique with higher reproducibility for fluid-to-debris component estimation with the added advantage of being a single stage procedure for both diagnosis (solid debris delineation) and management (drainage of collection) in the same sitting. Recently role of diffusion weighted MRI and positron emission tomography/CT with ¹⁸F-FDG labeled autologous leukocytes is also emerging for detection of infection noninvasively. Comparative studies between these imaging modalities are still limited. However we look forward to a time when this gap in literature will be fulfilled.

Keywords: Acute pancreatitis, Contrast-enhanced computed tomography, Magnetic resonance imaging, Endoscopic ultrasound, Positron emission tomography scan, Pancreatic fluid collections, Acute necrotic collections, Acute peripancreatic fluid collections, Pseudocysts, Walled-off necrosis

Core tip: Contrast-enhanced computed tomography is widely used imaging modality for the diagnosis and staging of acute pancreatitis due to its excellent capacity to demonstrate early inflammatory changes as well as local complications including fluid collections, However, magnetic resonance imaging may be a better imaging technique due to its, nonionizing nature, higher soft tissue contrast resolution, better safety profile of intravascular contrast media, noninvasive evaluation of pancreatic duct integrity and also has superiority in discrimination of internal consistency of pancreatic collections which is useful in further management plan. Role of endoscopic ultrasound and other newer techniques is still in evolving phase.