Pancreatic Pseudocyst



Pancreatic Pseudocyst


Brooke R. Jeffrey, MD

Michael P. Federle, MD, FACR





Key Facts


Imaging



  • Collection of fluid, tissue, debris, pancreatic enzymes, and blood surrounded by fibrous capsule



    • Develops after 4 weeks of episode of acute pancreatitis


  • CECT or MR: Enhancement of fibrous pseudocapsule



    • No enhancement of pseudocyst contents


  • MRCP: Hyperintense cyst with dilated ducts


  • Gas within pseudocyst = infection or communication with gut


  • Pseudoaneurysms can be caused by or simulate a pseudocyst


Top Differential Diagnoses



  • Mucinous cystic neoplasm


  • Pancreatic serous cystadenoma


  • Pancreatic intraductal papillary mucinous tumor


Pathology



  • Fibrous capsule, no epithelial lining


Clinical Issues



  • Therapy: Conservative



    • Spontaneous resolution in 25-40% of patients


  • Percutaneous drainage



    • Symptomatic or infected cyst > 4-5 cm


  • Endoscopic internal drainage: Transduodenal or gastric stents


  • Surgical therapy: Internal (usually into stomach) or external drainage of cyst


Diagnostic Checklist



  • Rule out other cystic masses, especially mucinous neoplasms



    • Often requires aspiration and analysis of cyst contents







(Left) Coronal CECT demonstrates a large pseudocyst image causing marked extrinsic compression of the gastric antrum image. (Right) Endoscopic ultrasound in the same patient shows the large pseudocyst image in contact with the distal stomach. An endoscopic cyst drainage was performed and a pigtail catheter was placed into the pseudocyst via the stomach. This procedure was successful in relieving the patient’s symptoms of gastric outlet obstruction.






(Left) Coronal CECT demonstrates a focal area of arterial enhancement image in the lateral wall of a pancreatic pseudocyst, representing a pseudoaneurysm from the gastroduodenal artery. (Right) Selective catheter angiography of the gastroduodenal artery confirms the CECT diagnosis of a pseudoaneurysm image. This was successfully treated with coil embolization.



TERMINOLOGY


Definitions



  • Encapsulated peripancreatic fluid collection with fibrous pseudocapsule 4 weeks after episode of acute pancreatitis


IMAGING


General Features



  • Best diagnostic clue



    • Peripancreatic cystic mass with enhancing pseudocapsule


  • Location



    • 2/3 located in peripancreatic spaces, including lesser sac and anterior pararenal spaces


    • 1/3



      • Juxta- or intrasplenic, intrahepatic, psoas compartment, or mediastinum


  • Size: Varies from 2-10 cm


  • Morphology



    • Spherical to oblong


    • In contrast to true cysts, pseudocysts lack true epithelial lining


Radiographic Findings



  • ERCP



    • Communication of pseudocyst with pancreatic duct seen in 70% of cases; decreases over time


CT Findings



  • NECT



    • Homogeneous, hypodense lesion with near-water-density (“mature” pseudocyst)


    • High attenuation indicates blood and gas bubbles indicate infection


  • CECT



    • Enhancement of thin fibrous capsule, not of cyst contents


    • Pseudoaneurysm with arterial attenuation in cyst wall


MR Findings



  • T1WI



    • Hypointense; possibly hyperintense (with hemorrhage)


  • T2WI



    • Hyperintense (fluid)


    • Mixed intensity (fluid + debris)


  • T1WI C+



    • May show enhancement of fibrous capsule


  • MRCP



    • Hyperintense cyst contiguous with dilated pancreatic duct


Ultrasonographic Findings



  • Grayscale ultrasound



    • Usually solitary unilocular peripancreatic cystic mass


    • Multilocular in 6% of cases


    • Fluid-debris level and internal echoes due to autolysis (blood clot or cellular debris)


    • Septations (uncommon; sign of infection or hemorrhage or indentation by adjacent artery)


Angiographic Findings



  • Conventional



    • For confirmation and embolization of pseudoaneurysm



      • Splenic artery is most frequently involved, followed by inferior and superior pancreaticoduodenal arteries


Imaging Recommendations



  • Best imaging tool



    • CECT or MR, multiplanar


DIFFERENTIAL DIAGNOSIS


Mucinous Cystic Neoplasm



  • CT or MR: Multiloculated (locules ≤6) hypodense mass


  • Multilocularity or mural nodules favor tumor over pseudocyst


  • Often indistinguishable from pseudocyst by imaging alone


  • More common in women 40-50 years old (“mother lesion”)


Pancreatic Serous Cystadenoma



  • Benign pancreatic tumor


  • Most frequently seen in women 50-70 years old (“grandmother lesion”)


  • CECT



    • Honeycomb or “sponge” appearance ± central scar


    • Enhancement of septa delineating small cysts


    • Unilocular variant indistinguishable from pseudocyst by imaging


Pancreatic Intraductal Papillary Mucinous Neoplasm (IPMN)



  • Cystic lesion contiguous with dilated MPD sometimes indistinguishable from pseudocyst


  • Low-grade malignancy arises from MPD > branch pancreatic duct (BPD)



    • Main duct type causes gross dilatation of MPD ± cystic spaces


    • Side branch type usually arises in pancreatic head/ uncinate, resembling “cluster of grapes” or small tubular cysts


  • May be indistinguishable from chronic pancreatitis and pseudocyst


Cystic Neuroendocrine Tumor



  • Usually noninsulin-producing and nonfunctioning


  • Tumor: Cystic on NECT and nonenhancing on CECT



    • No pancreatic ductal dilatation


  • Diagnosis best by endoscopic US-guided aspiration and biopsy


Congenital Cysts



  • Associated with von Hippel-Lindau and ADPKD


  • Rare, usually small and multiple nonenhancing cysts


PATHOLOGY


General Features



  • Etiology



    • In 10-20% of patients, acute peripancreatic fluid encapsulates after 4 weeks and forms pseudocyst




      • Chronic alcoholism (75%)


      • Abdominal trauma (13%): Major cause in children


      • Cholelithiasis, pancreatic carcinoma, idiopathic, other causes


  • Genetics



    • Genetic predisposition to pancreatitis in some patients even with minimal alcohol intake


  • Associated abnormalities



    • Walled-off pancreatic or peripancreatic necrosis



      • Combination of pancreatic fluid and necrotic debris


      • Sequelae of acute necrotic collection


      • Typically forms 4-6 weeks after episode of acute pancreatitis


Gross Pathologic & Surgical Features



  • Peripancreatic fluid collection surrounded by fibrous capsule


Microscopic Features



  • Absence of epithelial lining


  • Walls consist of granulation and fibrous tissue


CLINICAL ISSUES


Presentation

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Sep 20, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Pancreatic Pseudocyst

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