A: Pseudocyst size is less important than the clinical context of the patient. How certain are you that the cystic lesion noted on CT scan or ultrasound imaging is actually a pseudocyst? For instance, a middle-aged female patient with vague abdominal symptoms who is found to have a cystic mass of any size on abdominal imaging is much more likely to have a cystic neoplasm if there has been no antecedent history of pancreatitis. Likewise, patients with intraductal papillary mucinous neoplasm (IPMN) or mucinous cystadenoma of the pancreas (a premalignant condition) can occasionally present with obstructive pancreatitis. The presence of a cystic lesion at the onset of pancreatitis is crucial to distinguishing a neoplastic condition from a true pseudocyst, which is the consequence of a ductal disruption and the body’s containment of that disruption by a wall of inflammatory and fibrous tissue.
Pseudocysts that occur in the setting of chronic pancreatitis usually are the consequences of increased ductal pressure, with or without superimposed acute parenchymal inflammation. There is often a stone or a stricture downstream from the site of ductal disruption. If walled off, a pseudocyst occurs. Leaks that are not walled off may be associated with high amylase pleural effusions, pancreatic ascites, or fistulization into contiguous organs, including the bile duct, small bowel or colon. As a result of a fixed ductal obstruction, pseudocysts that occur in a patient with chronic pancreatitis are less likely to resolve spontaneously (Figure 1 on opposite page and Figure 2).
In contrast, most pancreatic fluid collections that occur in the setting of acute pancreatitis are not pseudocysts, and more than three-quarters resolve over 4 to 6 weeks. Pancreatic necrosis is also not a pseudocyst, although it too is associated with a ductal leak in most patients. Necrosis frequently results in a collection of debris-filled pancreatic juice that is anatomically constrained by the lesser sac. CT scanning notoriously overestimates the liquid component of the collection, and ultrasound (US) or endoscopic ultrasound (EUS) may be required to distinguish this from a pseudocyst. Other clues include the irregularity and variable thickness of the wall, extension into the pelvic gutters, nonenhancement of the pancreatic parenchyma on the early arterial phase of a pancreatic protocol CT, and the stormy clinical course of the patient to include multisystem organ failure (MSOF) and bacterial translocation from the gut with superinfection of the necrotic tissue and fluid. Pseudocysts may be a consequence of evolving pancreatic necrosis, but this occurs several months after a severe attack of pancreatitis and occurs when the majority of necrotic tissue has liquefied and a true fibrous “rind” has formed around the fluid collection.
Pseudocysts that occur in the setting of acute pancreatitis are usually spherical, take 6 to 8 weeks to “mature,” and historically were felt to be associated with a high complication rate if not treated. This was at a time that treatment consisted primarily of surgical cystgastrostomy or Roux-en-Y cystojejunostomy. The maxim was that pseudocysts 6 cm or larger present for more than 6 weeks required drainage. It was in that background that percutaneous drainage of pseudocysts was popularized in an attempt to avoid surgery. Subsequently, endoscopic drainage was described as a means to avoid an indwelling percutaneous catheter. The latter resulted in a long-term pancreatic fistula in 10% to 20% of patients, most of whom had a downstream ductal obstruction or the disconnected pancreatic duct syndrome.
Seminal work from the University of Minnesota randomizing asymptomatic patients with acute pseudocysts to surgery or expectant follow-up changed my treatment paradigm almost 20 years ago. Those investigators found a relatively low risk of pseudocyst complications as long as the diameter of the pseudocyst was stable or decreasing in size. Additional studies suggested that the 7% to 25% complication rates in patients with pseudocyst occurred early in the clinical course or in the setting of enlarging fluid collections, almost all of whom were symptomatic. These complications can include bleeding with pseudoaneurysm formation, obstruction of contiguous organs (bile duct, cholestasis/jaundice; stomach/duodenum, gastric outlet obstruction), cyst infection, and occasional cyst leak with free rupture, but more commonly fistulization into contiguous organs.
Figure 1. Abdominal CT demonstrates a 10-cm pseudocyst (arrow) in an asymptomatic patient with hereditary pancreatitis. The patient had previous cystogastrostomy 20 years prior.
Figure 2. Endoscopic compression by pseudocyst in the patient depicted in Figure 1. Because the patient had splenic and portal vein thromboses with varices, she was initially followed conservatively elsewhere.
Source: Kozarek RA
What has changed to allow us to follow a patient with a 10-cm pancreatic fluid collection and not recommend intervention? Imaging has improved dramatically, and CT scans, secretin magnetic resonance cholangiopancreatography (MRCP) scans, and EUS with or without sampling of the cyst fluid have improved our ability to distinguish cystic neoplasms from pseudocysts, thereby eliminating patients with potential neoplasms early in the course. We also have a better understanding of acute pancreatic fluid collections because serial CT scans have demonstrated that most collections associated with acute pancreatitis resolve. Moreover, as noted previously, the majority of patients with an enlarging collection or complication of pseudocyst are not asymptomatic. Finally, we now recognize that evolving pancreatic necrosis is not a pseudocyst and that the morbidity and mortality associated with this condition are at least a log factor higher than in the setting of an acute or chronic pancreatic pseudocyst.
So, if I am certain that this 10-cm fluid collection is a pseudocyst, that the patient is eating and is asymptomatic, and that the cyst is stable or slowly being reabsorbed, why not follow it? How often the patient needs to be scanned, sounded, or palpated is contingent upon whether the patient is recovering from acute pancreatitis or if the cyst was found incidentally in a patient with chronic pancreatitis. In the former setting, repeat imaging every 4 to 6 weeks seems reasonable, eventually increasing imaging intervals to every 5 to 6 months. In patients with chronic pancreatitis, a repeat CT or US should be considered at 1 month and repeated at 3 and 9 to 12 months if the patient remains asymptomatic. Alternatively, because pseudocysts that occur in patients with chronic pancreatitis usually have a downstream stone or stricture preventing ultimate pseudocyst resolution, this latter situation is considered by some practitioners to be an absolute indication for intervention, regardless of the presence of symptoms.
Leung J, Lo SK, eds. Curbside Consultation in Endoscopy: 49 Clinical Questions, Second Edition (pp 199-201) © 2014 SLACK Incorporated.
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