| Keywords
Pancreatic pseudocyst, endoscopic ultrasound,
endoscopic retrograde cholangio-pancreatography, pancreatic
cysts, pancreatic cyst-gastrostomy
Abstract
The diagnosis and treatment of pancreatic
pseudocysts has traditionally been performed by CT/US guidance.
With the emergence of linear endoscopic ultrasound, endoscopists
and gastroenterologists have become increasingly capable of
managing patients with pseudocysts. Linear EUS provides a
new method for imaging, aspirating, and draining pseudocysts.
Under EUS imaging, pseudocysts are characteristically unilocular
without evidence of the small, thin septations seen in mucinous
cystadenomas. The fluid aspirated from pancreatic pseudocysts
is often dark in color and contains inflammatory cells such
as pigment-laden histiocytes. Small, thin-walled pseudocysts
that are directly adjacent to the stomach or duodenal are
the ideal candidates for EUS-guided, transmural stenting of
pseudocysts.
Introduction
Pancreatic pseudocysts are chronic fluid-filled
cavities associated with inflammatory conditions of the pancreas.
Acute episodes of pancreatitis that result in tissue necrosis
or disruption of a pancreatic duct are the most common causes
of a pancreatic pseudocyst. The fluid contained within pseudocysts
is composed of activated pancreatic enzymes and inflammatory
debris. Because the fluid cavities are not lined with an epithelium,
pseudocysts are not true cysts and are, instead, surrounded
by chronic reactive granulation tissue[1]. The therapeutic
approach to a pancreatic pseudocyst is dependent upon an accurate
diagnosis and a thorough understanding of the pathogenesis
of the underlying disease.
Body
Definitions of Pancreatic Fluid
Collections[2]
Acute collections
Acute peri-pancreatic fluid collections often develop in patients
with acute pancreatitis. The fluid consists of large amounts
of pancreatic enzymes, inflammatory debris, and necrotic tissue.
The collections may be small and in direct continuity with
the pancreas or large and remote from the pancreas. In cases
of severe acute pancreatitis with necrosis and ductal disruption,
the fluid collections often communicate directly with a defect
in the pancreatic ductal system.
Phlegmons
Acute pancreatic phlegmons develop commonly in the setting
of acute pancreatitis as a result of focal damage to the pancreas.
Phlegmons consist of focal tissue necrosis, inflammatory debris,
and necrotic fat. Phlegmons develop within a few days of severe
pancreatitis and may persist for several weeks or months and
finally resolve. The most serious complication of a pancreatic
phlegmon is infection. This often requires a surgical debridement
for resolution.
Abscesses
Pancreatic abscesses are relatively rare. They develop in
the setting of acute pancreatitis with necrosis. An abscess
develops from an infection of an acute fluid collection or
phlegmon. They most commonly occur 3-6 weeks after severe
acute pancreatitis and often require drainage.
Chronic pseudocysts
Pseudocysts are chronic fluid collections that consist of
pancreatic secretions and inflammatory debris. They may develop
after an episode of acute pancreatitis or insidiously in the
setting of chronic pancreatitis. Small pancreatic pseudocysts
are usually intra-pancreatic and have a thin wall. Large pseudocysts
are usually in continuity with the pancreas, but they may
be so large that they become remote from the pancreas. Thick-walled
pseudocysts rarely communicate with the pancreatic ductal
system.
Clinical manifestations
Pain from distention and compression
Most pancreatic pseudocysts are uncomplicated and
result in few or minor symptoms. The larger the pseudocyst,
the more likely it is to cause symptoms because they will
compress or obstruct the duodenum, bile duct, or stomach.
The most common compliant is early satiety, nausea, and vomiting,
particularly after meals. The symptoms of a pancreatic pseudocyst
may be mimicked by chronic pancreatitis.
Indications for drainage
The traditional guidelines for management of pseudocysts
was to recommend drainage if the pseudocyst was greater than
6cm after a 6 week observation period[3]. With improvements
in the understanding of the natural history of pseudocysts,
it is now clear that the vast majority of pseudocysts resolves
spontaneously and should not be drained unless there are complications
or persistent symptoms. The abdominal pain arising from a
pancreatic pseudocyst is often cured with surgical resection[4].
Bleeding
Acute or chronic GI bleeding develops in 10-20% patients
with chronic pseudocysts. Acute GI bleeding may originate
from gastric varices, a common complication of pseudocysts
located in the body and tail of the pancreas. Portal hypertensive
gastropathy and superficial ulcers are other potential causes
of acute GI bleeding. Occasionally, the bleeding will take
place within the pseudocyst cavity, usually from pseudoaneurysms
in the wall[5, 6]. The bleeding is usually sudden and arterial
and may result in sudden and massive distention of the pseudocyst[7].
It may be treated with arterial embolization using selective
angiography[8]. Erosion and rupture of the pseudocyst into
the portal venous system is very rare[9].
Infection
Infection of pancreatic pseudocysts is relatively
common and the origin is presumed to be the migration of enteric
organisms from the intestinal tract[10]. The infections may
be mild and transient but more commonly are severe and result
in a sepsis syndrome. The infections are caused by a proliferation
of enteric organisms in the protein-rich fluid of the pseudocyst.
Severe infections occur when the infected fluid communicates
with the peritoneal cavity or the bloodstream.
Splenic vein thrombosis
This is a common complication of pancreatic pseudocysts,
particularly when the pseudocyst is located in the body or
tail of the pancreas and is associated with chronic pancreatitis[11].
The thrombosis presumably occurs in the setting of splenic
vein compression by the pancreas and/or the pseudocyst. Splenic
vein thrombosis will result in dilation of the short gastric
veins and splenomegaly. Extension of the thrombus into the
portal vein is rare. The thrombosis is rarely reversible.
Pancreatic biliary ductal obstruction
Obstruction of the pancreatic-biliary ducts is relatively
common, particularly when the pseudocyst is located within
the head of the pancreas. Local compression is the most common
cause of ductal obstruction, although a direct fibrotic involvement
of the ducts is occasionally seen. Obstruction of the distal
bile duct with resulting jaundice is the most common scenario.
Drainage of a pseudocyst will resolve the obstruction of the
duct, particularly the bile duct. With long-term obstruction
of the pancreatic-biliary ducts, stones, sludge, and debris
is relatively common and will contribute to the obstruction.
Imaging of Pseudocysts
CT scanning
Pseudocysts are readily seen with CT scanning and
appear as low attenuation lesions within or adjacent to the
pancreas (Figure 1). Chronic pseudocysts are most commonly
round and surrounded by a thick, dense wall. Large pseudocysts
may appear in mediastinum, pelvis, or involve the mesentery.
Prominent vessels along the pseudocyst wall are common and
may represent para-gastric varices and thrombosis of the splenic
vein. More importantly, pseudoaneurysms are noted within the
pseudocyst wall in 10% of patients and are an important source
of bleeding complications[12]. Although pseudocysts are most
commonly unilocular, fibrotic strands within the cavity may
cause multiple septations. The pseudocyst cavity may also
contain debris, blood, or infections that appear as high attenuation
areas within the fluid-filled cavity. Cystic neoplasms of
the pancreas are frequently mistaken with CT scanning as pancreatic
pseudocysts[13].
ERCP
Pancreatography in the setting of a pseudocyst often
reveals a diffusely abnormal duct with changes of chronic
pancreatitis evident. The main pancreatic duct may be partially
or completely obstructed by ductal fibrosis or extrinsic compression
by the pseudocyst (Figure 2). Pancreatic ductal leaks are
common in the setting of pancreatic pseudocysts. Large leaks
may originate from the main pancreatic duct and small leaks
may originate from secondary radicals. Magnetic resonance
imaging may be used as an alternative to ERCP and will provide
images of the ductal system and adjacent pseudocysts[14].
EUS
The role of EUS in the diagnosis and treatment of
pseudocysts has been expanding as its ability to diagnose
and drain pseudocysts has been documented[15, 16]. Pseudocysts
appear as anechoic, fluid-filled structures adjacent to the
UGI tract and the pancreas (figure 3). Fluid collections associated
with acute pancreatitis will not be surrounded with a well-defined
wall, whereas a thick, hyperechoic rind often surrounds pseudocysts.
Calcifications within the wall are rare. Within the pseudocyst
cavity is fluid without air. Debris in the dependent portion
of the cavity is common and may represent blood, infection,
or necrotic material (figure 4). Color Doppler of the wall
will often reveal multiple, prominent vessels, including para-gastric
varices. Evaluation of suspected pseudocysts with EUS prior
to drainage is important for confirming the diagnosis, determining
the precise location, and determining the thickness of the
pseudocyst wall[17, 18]. Catheter probe endosonography can
also be used to localize pseudocysts[19].
Cyst aspiration
Fine needle aspiration of pseudocysts is performed
for diagnostic or therapeutic purposes[20]. Since pseudocysts
may be confused with true epithelial cysts of the pancreas,
aspiration of cysts is performed to differentiate between
pseudocysts and a wide variety of benign and malignant cystic
neoplasms of the pancreas[21, 22]. If an infection of a pseudocyst
is suspected, the cyst may be aspirated for culture. Therapeutically,
pseudocysts are completely aspirated with the hope that they
may not recur.
Fine needle aspiration of pseudocysts can
be performed with a variety of techniques. The most common
approach is to use CT/US guidance. A needle is placed through
the abdominal wall and into the cystic cavity; fluid is aspirated.
EUS can also be used to guide endoscopic cyst fluid aspiration.
EUS has two major advantages, greater ability to locate small
pseudocyst and a shorter, more direct path to the pseudocyst.
The aspirated fluid from a cystic lesion is examined cytologically
for evidence of inflammatory cells. The presence of pigmented
histiocytes is nearly diagnostic of a pseudocyst (figure 5).
If there is evidence of epithelial cells with the cyst fluid,
this should raise the suspicion of a cystic neoplasm rather
than a pseudocyst[23]. The presence of neutrophils in the
fluid suggests an acute infection of pseudocyst fluid. Unfortunately,
cytologic evaluation of cyst fluid is made difficult by a
high frequency of acellular, non-diagnostic specimens. To
complement the findings of cytology, cyst fluid tumor markers
are often used to assist in differentiating between pseudocysts
and cystic neoplasms. CEA is the most commonly used marker
because mucinous cystic neoplasms secrete CEA into cystic
fluid, whereas pseudocysts should have relatively low levels
of CEA[24]. There is significant overlap between the CEA values
of pseudocysts and mucinous cystadenomas, but it is rare for
pseudocysts to have a CEA value of more than 100 ng/ml.
If there is any concern about an infected
pseudocyst, aspirated cyst fluid should be sent for culture
and sensitivity. Although gram negative, enteric bacteria
are the most common organism infecting pseudocyst fluid, occasionally
gram-positive bacteria may cause an infection. Pseudocyst
fluid aspirated under EUS guidance may be sent for culture,
but little information is available regarding the degree of
contamination that may occur as a result of the EUS needle
passing through the echoendoscope and the gastro-duodenal
wall.
Cyst drainage
Pancreatic pseudocysts may be drained using a variety
of approaches. External drainage using CT/US guidance is the
most common approach[25]. With this technique, a drainage
catheter is placed percutaneously into the fluid cavity, and
fluid is drained through a pigtail catheter. Three-dimensional
ultrasonography has been reported useful for the guidance
of catheters into cyst cavities and avoiding vessels[26].
The fluid is collected over several weeks into an external
collection system. When the drainage output becomes minimal,
the catheter is removed. Contrast injection into the cyst
cavity will demonstrate the size of the cavity and this finding
can be used to monitor the progress of the chronic drainage.
This technique is highly successful at resolving pseudocysts,
but is plagued by infections and the need for an external
drain. The reported success rate for ultrasound-guided pseudocyst
drainage is 50%[27]. Unsuccessful drainages are usually caused
by large ductal leaks or obstruction of the main pancreatic
duct[28].
Surgical drainage of pseudocysts is accomplished
by providing a large anastamosis between the pseudocyst cavity
and the stomach or small bowel[29]. This approach to drainage
is often reserved for those patients that cannot tolerate
chronic external drainage[30]. The anastamosis should be placed
in the most dependent portion of the cystic cavity in order
to maximize the chances of complete drainage. The anastamosis
usually remains patent and functional for several months.
When the pseudocyst has resolved, the lack of drainage results
in the spontaneous closing of the anastamosis. Success rates
for surgical drainage of pseudocysts are very high, approaching
100%[31]. If the pseudocyst is associated with an obstructed
main pancreatic duct, a pancreatico-jejunostomy drainage can
be used[32, 33]. A laparoscopic approach has been described
for lesser sac pseudocysts and reportedly takes an average
of 90 minutes to perform[34, 35]. Drainage and removal of
infected, necrotic pancreatic tissue can also be performed
laparoscopically[36]. Small intrapancreatic pseudocysts should
be not be drained surgically, but may be resected[37].
Endoscopic drainage of pseudocysts is the
newest approach. This technique is used for uncomplicated,
unilocular pseudocysts. Drainage is accomplished with either
a transpapillary approach with ERCP or direct drainage across
the stomach or duodenal wall[38]. A transpapillary approach
is used when the pseudocyst communicates with the main pancreatic
duct, usually in the head of the pancreas[39]. This approach
is also successful for patients with pancreatic duct disruption
or after surgical drainage[40, 41]. A transgastric or duodenal
approach is used when the pseudocyst is directly adjacent
to the gastro-duodenal wall. To determine the size and location
of the pseudocyst, and to measure the thickness of the pseudocyst
wall, EUS is the test of choice[42] (figure 6). A wall thickness
of more than 1cm or the presence of large intervening vessels
or varices will preclude the possibility of endoscopic drainage.
Transgastric or transduodenal stenting of
pseudocysts may be performed using an endoscopic approach
or using EUS to introduce the guidewire into the pseudocyst
cavity. The endoscopic approach is dependent upon the presence
of a ?bulge? into the lumen of the stomach or duodenum in
order to determine the entry site for catheterization (figure
7). This approach has several inherent risks, including missing
the pseudocyst, injuring intervening vessels, and sub-optimal
placement of the drainage catheter. Therapeutic endosonoscopes
now make it possible to diagnose and treat pseudocysts with
EUS-guided transmural stenting (figure 8)[43]. Several series
have described the deployment of a 7 Fr stent that is introduced
with a needle knife catheter (figure 9)[44]. A new large channel
endosonoscope allows the use of 10Fr stents across the stomach
or duodenum[45]. In a small series, the EUS approach has resulted
in success a rate of more than 90% in patients with chronic
pseudocysts[46]. The recurrence rate after endoscopic drainage
is low, 4%, and the complication rate is less than 16%[47].
EUS is also capable of guiding the drainage of infected pseudocysts
using naso-cystic drains (figure 10)[48, 49]. It may even
be possible to drain infected necrotic pancreatic tissue using
EUS and endoscopic techniques[49, 50].
|
 |
Figure
9 |
Figure 10 |
Although endoscopic drainage using transmural
stenting often results in the drainage of pseudocyst contents
into the stomach, it is possible to use a combination of endoscopy
and ultrasonography to guide the drainage percutaneously[51].
A similar combination of techniques has been used for internal
drainage of pseudocysts[52].
Summary
In conclusion, pancreatic pseudocysts are
localized collections of fluid originating from the pancreas.
Although US/CT scanning is the traditional test for detecting
and draining pseudocysts, EUS is an emerging endoscopic technique
that will be increasing used in the management of patients
with symptomatic pseudocysts.
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