Pancreatic pseudocysts are common sequelae of acute pancreatitis or chronic pancreatitis, and the most common cystic lesion of the pancreas. They are important both in terms of management and differentiation from other cystic processes or masses in this region.
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Terminology
The following are the latest terms according to the updated Atlanta classification to describe fluid collections associated with acute pancreatitis 10,11:
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fluid collections in interstitial edematous pancreatitis
acute peripancreatic fluid collections (APFC): in the first 4 weeks: non-encapsulated peripancreatic fluid collections
pseudocysts: develop after 4 weeks; encapsulated peripancreatic or remote fluid collections
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fluid collections in necrotizing pancreatitis
acute necrotic collection (ANC): in the first 4 weeks; non-encapsulated heterogeneous non-liquefied material
walled-off necrosis (WON/WOPN): develop after 4 weeks; encapsulated heterogeneous non-liquefied material
Clinical presentation
Pancreatic pseudocysts are frequently found on imaging follow-up of pancreatitis, and may in themselves be asymptomatic for some time. Presentations attributable to a pseudocyst include:
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mass effect
biliary obstruction
gastric outlet obstruction
secondary infection
Pathology
Pseudocysts occur from disruption of pancreatic duct structure with resulting leakage and accumulation of pancreatic juice resulting in hemorrhagic fat necrosis. They are not lined by epithelium (thus, “pseudocysts”), rather a severe inflammatory reaction results in encapsulation of the cyst by fibrosed granulation tissue. This usually takes 4-6 weeks 8,9. In approximately 50% of cases, the cyst retains a communication with the pancreatic duct 2. Such cysts are more problematic to treat, and are more likely to recur.
Etiology
acute or chronic pancreatitis (most common)
iatrogenic, e.g. post partial gastrectomy 12
Subtypes
Radiographic features
Pseudocysts are fluid-filled oval or round collections with a relatively thick wall. They can be multiple and are most commonly located in the pancreatic bed. However, they can be found anywhere from the groin to the mediastinum and even in the neck, having ascended in the retroperitoneum via the diaphragmatic hiatuses into the mediastinum 5.
It is not possible to reliably distinguish infected from non-infected pseudocysts on imaging alone 9.
Plain radiograph
Abdominal radiographs are often not sensitive in the workup for a pancreatic pseudocyst. However, if the cyst is large, it may demonstrate a gastrocolic separation sign which suggests fluid at the peripancreatic region and into the lesser sac 15.
Ultrasound
Hypoechoic or anechoic collections, with dependent low-level echoes representing debris, are often seen 8.
CT
Pseudocysts appear as well-circumscribed, usually round or oval peripancreatic fluid collections of homogeneously low attenuation, that are usually surrounded by a well-defined enhancing wall 10. Calcification of the wall of a pseudocyst is rare and an alternative diagnosis should always be considered 22,23.
According to the revised Atlanta classification, pseudocysts contain no non-liquefied components within the fluid collection, as even minimal amounts of fat or soft-tissue attenuation would make it a WON 10,21.
MRI
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T1
hypointense (fluid signal) center
wall demonstrates mild early enhancement, which progressively becomes more intense 7
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T2
hyperintense (fluid signal)
layering or dependent debris, highly specific 6
Treatment and prognosis
Although pancreatic pseudocyst may regress on its own and requires no further treatment, interventions are required in selected cases, particularly those complicated with infections, large size causing mass effect symptoms such as gastric outlet obstruction, bowel obstruction, hydronephrosis and biliary obstruction, diameter increasing in size or greater than 5 cm, recurrence following previous resection or aspiration, and persistent symptoms 14,16,17.
Treatment options include:
open surgical debridement, or cystenterostomy with a Roux-en-Y jejunal loop 3
endoscopic drainage into the stomach (or duodenum) termed a cyst-gastrostomy 3
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percutaneous drainage
remains somewhat controversial, although increasingly accepted 1,2
many centers report high safety and efficacy 1
critics raise concern regarding potential reaccumulation and fistula formation to the skin (especially in patients with severe pancreatitis) 4
octreotide infusion: decreases amount of pancreatic secretions
Cysts that do not communicate with the pancreatic duct usually do not recur and are unlikely to create fistulae 2.
Differential diagnosis
General imaging differential considerations include:
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cystic lesions of the pancreas
do not usually have internal debris
may be microcystic in the case of serous cystadenoma
dilated duct communicating with a side branch may represent an IPMN
often requires endoscopic FNA for definitive diagnosis 6
choledochal cyst (especially for ultrasound)
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very thin walls
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peripancreatic collection of acute pancreatitis
will not be round, but rather take on the contours of the space in which they are located
pseudocysts take ~4 weeks to form
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non-pancreatic pseudocyst 18
cystic fluid with low levels of amylase or lipase in the cystic fluid
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