A third of all patients with acute pancreatitis develop complications, and a quarter of those patients will not survive, but recovery is now expected for the remainder because of improvements in the diagnosis and management of acute pancreatitis.¹ The complications of acute pancreatitis can be local, regional, and/or systemic. The most important determinants of the severity of acute pancreatitis are infected local complications and persistent organ dysfunction,² which are the basis for classifying acute pancreatitis severity (Table 69-1).^3,4 This chapter focuses on the diagnosis and management of these important complications of acute pancreatitis.

The local complications of acute pancreatitis are related to fluid collections and tissue necrosis in and around the pancreas. These were defined by the Atlanta Symposium in 1992 by the terms pancreatic necrosis, pseudocyst, and abscess.⁵ However, these terms have been confusing and new terminology has been introduced in an attempt to reflect current understanding of the pathophysiology and CT scan morphology of the disease.⁶ Changes in the morphology of local collections can occur over time and these are now defined on the basis of their content, chronicity, and whether infection is present (Table 69-2).⁷

The revised Atlanta Classification uses a 4-week cutoff, and fluid collections present for less time are called either an acute pancreatic fluid collection (APFC) or acute necrotic collection (ANC).⁶ These acute collections can either spontaneously resolve or progress to become “walled-off” or encapsulated, which is a reaction of the surrounding tissue to the enzyme-rich fluid. The resulting wall is usually well-defined on a CT scan after 4 weeks. A pancreatic pseudocyst is the term that has traditionally been applied to this encapsulated lesion, but it is now appreciated that the contents can be variable ranging from entirely fluid to containing solid necrotic tissue.⁶ When a fluid collection has developed in association with pancreatic necrosis, the revised Atlanta Classification recommends the term “walled off necrosis” (WON). The term pseudocyst has now a more restricted definition and is only applied when the content is entirely fluid and has been present for 4 or more weeks.^6,7

Acute Pancreatic Fluid Collections

DESCRIPTION

Acute fluid collections demonstrate no solid content or defined wall, and typically exist adjacent to the pancreas. These collections occur in 30% to 50% of cases and contain a mixture of inflammatory exudate and/or enzyme-rich pancreatic secretions from small side-branch ducts. The leaked pancreatic secretions can track widely through the retroperitoneum and mediastinum and may directly lead to pancreatic ascites and/or pleural effusions. The most common routes of extension are into the lesser sac, behind the pancreatic head, behind the left and right colon anterior to the psoas muscle, and into the small bowel mesentery, and may bulge through the transverse mesocolon.

DIAGNOSIS

Acute fluid collections usually start to develop in the first 48 to 72 hours after the onset of symptoms. Contrast-enhanced CT (CECT), magnetic resonance imaging (MRI), transabdominal ultrasound (US), or endoscopic ultrasound (EUS) can be used to confirm the diagnosis. To distinguish an APFC from ANC, or more specifically determine whether there is necrosis within the collection, it is best to use MRI or US.⁶ However, the presence of necrosis within a collection can often be inferred by the extent and pattern of hypoperfusion on CECT.

MANAGEMENT

Acute fluid collections usually remain sterile and resolve spontaneously.⁸ However, these are the precursors of pancreatic pseudocysts. Large collections of fluid around or within the pancreas are more likely to be due to disruption of the main pancreatic duct and are more likely to persist for a number of weeks or continue to increase in size.

Acute fluid collections are rarely symptomatic and do not require active treatment. Intervention by drainage (endoscopic, radiological, or surgical) risks introducing infection into a sterile collection. An asymptomatic fluid collection is managed by observation alone, and only when infection is present is drainage necessary. There is no role for diuretics or peritoneal lavage.⁹ Rarely, leakage from a disrupted main pancreatic duct can be treated by endoscopic or surgical intervention. Endoscopic pancreatic duct stenting can be used across the sphincter of Oddi to decrease ductal pressure and facilitate drainage into the fluid collection through the disrupted duct to drain the collection directly or across the damaged duct to redirect drainage from the collection to the duodenum and to stent the duct to reduce the risk of stricture formation. Radiological percutaneous stenting in the presence of disrupted main pancreatic duct can result in an external pancreatic fistula. There is no role for the operative treatment of APFC.

The drainage of pleural effusions in patients with acute pancreatitis should be considered in the face of compromised respiratory function or inadequate oxygenation. Chronic pleural effusions may be due to an internal pancreatic fistula and are best treated with a chest tube, nasojejunal tube feeding, and a trial of somatostatin. Persistence or recurrence will require identification of a pancreatic leak by endoscopic pancreatography. Definitive treatment may require endoscopic or surgical internal drainage once a pseudocyst has developed, or rarely a distal resection of the pancreas if this will address the fistula.

Acute Necrotic Collections

DESCRIPTION

ANCs contain both solid material and fluid, but are not walled off by a fibrous capsule. A CECT will demonstrate hypoperfused pancreas associated with a fluid collection. The necrosis is associated with disruption to branch ducts and sometimes the main pancreatic duct. Over time the necrotic tissue demarcates, sequesters, and liquefies, forming part of the APFC. With persistence and maturation, an encapsulating wall forms, and after 4 weeks this is termed WON. Postnecrotic collections are usually sterile but infection can occur. The term pancreatic abscess has been abandoned⁶ because it does not distinguish between an infected acute fluid collection (AFC), infected pseudocyst, infected ANC, or infected WON.

DIAGNOSIS

Acute postnecrotic fluid collections are diagnosed by CECT, MRI, US, or EUS and usually after the first week from disease onset. An infected APFC can be diagnosed by the presence of gas within the collection on CT (Fig. 69-1) within 4 weeks of disease onset. The definitive diagnosis of infected APFC requires image-guided fine-needle aspiration (FNA) for Gram stain and culture or culture of fluid obtained from percutaneous drainage. In practice a FNA is rarely required to confirm infection.⁶ Endoscopic retrograde cholangiopancreatography (ERCP) can be used to determine whether there is any ductal communication associated with the collection, but this is rarely required and risks the introduction of infection.

Pseudocyst

A pseudocyst is a circumscribed collection that contains only fluid, has a well-defined wall, and has been present for 4 or more weeks after disease onset.⁶ In the original Atlanta Classification,⁵ a pseudocyst was defined as a collection of pancreatic juice enclosed by a wall of fibrous tissue, and there was no mention of the content. In practice, the lesion is either a fluid collection that does not contain necrosum, which when mature is best termed a pseudocyst, or a postnecrotic fluid collection that contains necrosum, which when mature is best termed WON. The result of this redefinition is that the term pseudocyst is applicable less frequently.

The precursor of a pseudocyst is the APFC, and it is differentiated from the latter by the presence of a well-defined wall (capsule) without an epithelial lining. This is in contrast to cystic neoplasms of the pancreas, which are characterized by an epithelial lining. This, however, is not an absolute distinction, as there may be discontinuous epithelium within cystic neoplasms (probably due to pressure atrophy) and partial epithelialization within chronic pseudocysts (facilitated by communication with the main pancreatic duct). In fewer than 20% of cases, more than one pseudocyst is present. Acute pseudocysts are located most often in close proximity to the pancreas, especially in the lesser sac (Fig. 69-2), but can be found in the pelvis, scrotum, mediastinum, or thorax.

PATHOGENESIS AND CLASSIFICATION

The development of a pseudocyst requires pancreatic duct disruption. This occurs with acute pancreatitis in 10% to 15% of cases, but also in the case of pancreatic duct trauma (usually to the pancreatic neck), and in chronic pancreatitis where there may be multiple pseudocysts due to duct obstruction.¹⁰ The leakage of enzyme-rich secretion incites a marked inflammatory reaction in the retroperitoneum, peritoneum, and serosa of adjacent viscera. As a result, the fluid is contained by a developing layer of granulation tissue and fibrosis that matures over time. If the communication between pancreatic duct and pseudocyst persists, the pseudocyst can continue to enlarge. The contents of the pseudocyst usually consist of a relatively clear, watery fluid. However, with hemorrhage it may contain clot and become xanthochromic. In the presence of infection, a pseudocyst will contain pus. If a fluid collection develops in the context of pancreatic necrosis, and it will contain solid tissue and should be termed WON.

Pseudocysts were classified by D’Egidio in 1991 (Table 69-3).¹¹ Type I pseudocysts occur after an episode of acute pancreatitis and are associated with normal pancreatic duct anatomy, and rarely communicate with the main pancreatic duct. Type II pseudocysts occur after an episode of acute or chronic pancreatitis and have a diseased but not strictured pancreatic duct, and there is often a communication between the duct and the pseudocyst. Type III pseudocysts occur in chronic pancreatitis and are always associated with a duct stricture and a communication between the duct and the pseudocyst.

COMPLICATIONS

Complications occur in about 10% of pseudocysts. The four most common complications of pseudocysts are infection, rupture, bleeding, or symptoms due to a mass effect.¹²

Pseudocysts are initially sterile, but infection can occur in up to 25% of cases.^12,13 The presence of sepsis due to an infected pseudocyst is an indication for drainage (see below).

The rupture of a pseudocyst can occur by erosion into adjacent organs, which may allow the pseudocyst to resolve or it may produce an internal cystoenteric fistula or fistula between the pancreas and other organs, including pleura, bronchus, and bladder. The term fistula is technically incorrect since the communication is not between two epithelial-lined structures. Rupture into the gastrointestinal tract may be associated with significant hemorrhage. Rupture into the peritoneum leads to pancreatic ascites and can be a dramatic presentation with acute abdominal pain and rigidity from chemical peritonitis.

Bleeding associated with a pancreatic pseudocyst can be life-threatening complication. There are several causes of bleeding. Bleeding may occur secondary to erosion and rupture into the gastrointestinal tract and presents as hematemesis and/or melena. More ominous is bleeding for the direct erosion of a significant visceral vessel, including the splenic, gastroduodenal, and middle colic vessels. The action of pancreatic enzymes (especially elastase) on the vessel wall can lead to thinning of the vessel wall with aneurysm and pseudoaneurysm formation (Fig. 69-3). This situation carries a high mortality (∼20%).¹⁴ The risk of bleeding is increased in the presence of local infection. If time and patient stability permit, it may be possible to perform a CT scan with arterial phase contrast to demonstrate the pseudoaneurysm and sometimes active bleeding. However, emergency selective splanchnic angiography is frequently required to delineate the site of bleeding and to embolize the culprit vessel, which is the preferred treatment (Fig. 69-4). Bleeding into a mature pseudocyst may be arrested by tamponade, although with less mature pseudocysts there is the risk of pseudocyst rupture with hematoma. Emergency surgery is rarely required and is often very difficult where the objective is to oversew the bleeding vessel. The options then include packing if there are concerns regarding recurrent bleeding. Occasionally it is possible to resect the pseudocyst with the body/tail of the pancreas, which is effective in preventing recurrent hemorrhage.

A large pseudocyst may exert a mass effect and thereby produce early satiety (stomach), partial or complete intestinal obstruction (duodenum, gastric outlet, esophagogastric junction, and rarely small or large bowel), cholestasis (bile duct), and venous thrombosis (portal, superior mesenteric, and splenic veins) leading to portal or segmental hypertension and varices. Mass effect is more likely when a pseudocyst is greater than 6 cm in diameter.¹²

DIAGNOSIS

With modern imaging there is a higher proportion of asymptomatic pseudocysts diagnosed. A pseudocyst may be suspected when a patient with acute pancreatitis fails to recover after the initial week of treatment or when, after initial improvement, symptoms return. In this setting there can be a moderate secondary rise in serum amylase/lipase. While a CECT is often performed, depending on the patient’s habitus and how much intestinal gas is present, ultrasonography can often make the diagnosis, and has the advantage of confirming whether the content is fluid only or whether there is solid necrosum present. EUS can be useful in distinguishing a pseudocyst from a cystic neoplasm because it often delineates internal septation better than CT scan.¹⁵ The advantage of CT scanning is that it is not operator dependent and is more useful in planning therapy. It will demonstrate the key features of a pseudocyst (ie, size, shape, wall thickness, and contents), the nature of the pancreas (ie, presence and extent of necrosis, diameter of pancreatic duct, and features of chronic pancreatitis, including atrophy and calcification), and, importantly, the relationship of these to the surrounding organs (Fig. 69-2), which is essential for planning internal surgical drainage. Triphasic helical CT scanning will delineate the regional arteries (to look for pseudoaneurysm formation) (Fig. 69-3) and veins (to look for thrombosis, cavernous transformation, and formation of varices).

ERCP is not routinely required as part of the diagnostic workup for pseudocysts. Over 90% of patients with a pseudocyst have some abnormality of the pancreatic duct, but not all require treatment. In symptomatic cases where treatment is likely, it is useful in planning further management and can be both diagnostic and therapeutic. Because of the risks of exacerbating pancreatitis, perforation, bleeding, and introducing infection, it is best that ERCP is done within 48 hours of any planned drainage procedure. The unique diagnostic contribution of ERCP is to accurately delineate a communication between the main pancreatic duct and the pseudocyst, which occurs in up to a half of patients. A communication of this type is a relative contraindication to external drainage of a pseudocyst.¹⁶ The classification of the main pancreatic duct by ERCP has been shown to assist in selecting the type of treatment, where the presence or absence of a stricture, communication, and obstruction is an important feature to note.¹⁷ Magnetic resonance cholangiopancreatography (MRCP) may be used to assess pancreatic and biliary duct morphology instead of ERCP and in some centers has replaced ERCP in its diagnostic role. MRCP has the advantage of being noninvasive with similar diagnostic accuracy to ERCP, but lacks any potential therapeutic intervention.¹⁸

Diagnosing a complication in a known pseudocyst is usually straightforward. The rupture of a pseudocyst into the peritoneal cavity is associated with the onset of acute abdominal pain and signs of peritonitis. This is in contrast to the spontaneous decompression of a pseudocyst into an adjacent organ, which usually results in the relief of symptoms. Infection of a pseudocyst is accompanied by signs of sepsis. Infection can be confirmed with image-guided FNA for Gram stain and bacterial culture. Bleeding usually results in an increase in abdominal pain and possible syncope, tachycardia, and hypotension. A drop in hemoglobin concentration is expected.

Although cystic neoplasms are rare, they can be mistaken for pseudocysts. Absence of an antecedent history of acute pancreatitis, elevation of cyst fluid carcinoembryonic antigen (CEA) or carbohydrate antigen (CA 19-9), and/or the presence of internal septations should suggest this diagnosis. If EUS is available, it will enable the identification of septations (usually microcystic pattern for serous lesions or macrocystic pattern for mucinous lesions), mural nodules, echogenic debris, and calcification. It may also allow aspiration of fluid content for analysis. Pseudocysts usually contain fluid with elevated amylase (>5000 U/mL) and an absence of tumor markers, but this should not be relied upon for a definitive diagnosis.¹⁹

INDICATIONS FOR INTERVENTION

The natural history of a pseudocyst is not easy to predict. Spontaneous resolution occurs frequently and usually within 6 weeks. Size alone is a poor predictor because resolution can occur even with very large pseudocysts. When larger than 6 cm in diameter and in the case of continued enlargement, a pseudocyst is more likely to persist and develop complications. Persistence is also more likely if there is a distal stricture of the main pancreatic duct and a proximal communication between the main pancreatic duct and the pseudocyst.

The two principal indications for treating pancreatic pseudocysts are to relieve symptoms and to treat complications. In the absence of symptoms or evidence of enlargement, conservative management is usually reasonable. A traditional approach that dictated treatment of all pseudocysts that have been present for more than 4 to 6 weeks is no longer justified.²⁰ The clinical decision about whether a pseudocyst in a particular patient requires active intervention can be difficult. The desire to allow time for spontaneous resolution to occur must be balanced against the risk of complications while waiting for cyst wall maturity. The traditional indication for treatment was the development of pseudocyst complications. Now the motivation is to prevent complications. An enlarging asymptomatic pseudocyst that has been present for 6 weeks is usually treated. A natural-history study from India indicates that asymptomatic pseudocysts less than 7.5 cm in diameter and without internal debris will resolve spontaneously on an average of 5 months.²¹ The mean diameter of pseudocysts requiring treatment is about 9 cm.^22,23 While there has been a trend toward conservative management, there has been an increase in the number of ways to treat a pseudocyst, including open surgical, laparoscopic, endoscopic, and radiological techniques.

Two important rules in the treatment of pseudocysts are that a cystic neoplasm must not be treated as a pseudocyst and elective external drainage should not be done if there is downstream and unrelieved pancreatic ductal obstruction because of the high risk of an external pancreatic fistula. The approach to treatment (Table 69-4) depends on the features of the pseudocyst, the state of the main pancreatic duct (eg, stricture or communication), and the fitness and level of symptoms of the patient. Also important is the level of available expertise and experience with the various treatment modalities.

The following general features of a pseudocyst are important in considering the most appropriate treatment:

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  The thickness of the pseudocyst wall, which is usually a function of the duration of the pseudocyst. This is important because adherence of the wall is more likely with maturity and is relevant for wall-opposing metal stents and for safely securing sutures for surgical drainage procedures.

  
  
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  The location of the pseudocyst. If adherent to the stomach or duodenum, the options are different than if the pseudocyst is deep within the retroperitoneum and covered by bowel loops.

  
  
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  The contents of the pseudocyst. The presence of blood may indicate the need for prior embolization of a pseudoaneurysm. Pus will require drainage, either internally or externally. The presence of solid necrosum suggests the lesion is in fact WON and may require some form of necrosectomy.

  
  
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  The number of pseudocysts. If multiple pseudocysts are present, then minimally invasive approaches are less feasible. Conservative management is less appropriate for multiple pseudocysts.

  
  
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  The etiology of the pseudocyst. If there is evidence of acute-on-chronic pancreatitis, different treatment may be required than if it has arisen after the first episode of acute pancreatitis.

  
  
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  The main pancreatic duct anatomy and degree of disruption. The pancreas and the pancreatic duct require separate consideration in planning the treatment of a pseudocyst. The pancreas may warrant treatment in its own right, especially if there is a ductal stricture, a dilated duct, regional disease, or a mass warranting resection.

TREATMENT OPTIONS

Although there has been a trend toward more conservative management of pseudocysts, especially in the absence of symptoms or complications, there has been an increase in the number of treatment options available (Table 69-5).²⁴ The most effective and reliable means of treating a pseudocyst is probably still by internal drainage by an open surgical approach, but there is a lack of comparative studies between surgical, endoscopic, and radiological treatments. Despite this, less invasive options are now being used more frequently.

Radiological Treatment

The first description of direct percutaneous aspiration and external drainage using radiologic guidance was in the early 1980s. This technique has become widely practiced, with a reported morbidity of between 10% and 30%. It can be used with an immature pseudocyst wall, although the risk of complications is higher in this setting. Percutaneous drainage is best suited to D’Egidio type I pseudocysts in which there is no significant underlying duct abnormality or communication between the duct and pseudocyst. In simple, uncomplicated pseudocysts, percutaneous drainage is usually successful but is rarely necessary since this group is rarely symptomatic, has the lowest complication rate, and has the best chance of spontaneous resolution.

The introduction of a transgastric approach to percutaneous drainage has almost abolished the problem of external pancreatic fistulas (Fig. 69-5).^24,25 This produces a percutaneous cystogastrostomy but requires an initial period of external transgastric drainage and then subsequent internalization at about 2 weeks. Internalization can be facilitated with a concurrent endoscopic view, especially when using double pigtail catheters. Endoscopy is used to remove the catheters when the pseudocyst has resolved on imaging. A well-matched population-based study comparing percutaneous (n = 8121) with open surgical drainage (n = 6409) in 14,914 patients with pancreatic pseudocysts revealed a longer length of hospital stay and twice the mortality (5.9 vs 2.8%) for percutaneous drainage.²⁶ Currently there is a limited role for percutaneous catheter drainage of pseudocysts, but this is most likely to be used in unfit patients and those who are unstable with an infected pseudocyst.

Endoscopic Treatment

There has been significant upsurge in the use of endoscopic treatment for pseudocysts over the last decade. Endoscopic transmural drainage is now widely used. It is wise to perform cross-sectional imaging first to ensure sound apposition of cyst and stomach. While a visible bulge from the pseudocyst may be apparent on endoscopy, EUS guidance during these procedures is now the standard of care. EUS allows greater accuracy and safety by confirming the anatomic route, assists in ruling out a cystic neoplasm, and can identify blood vessels, reducing the risk of bleeding. There are several options available once the cyst is punctured and a guidewire inserted into the cavity. If there is no solid material found in the pseudocyst, then a single pigtail catheter might be all that is required. Recurrence is a risk, especially if there is underlying communication with the main pancreatic duct. While multiple pigtail stents can be inserted following balloon dilation of the track, it is now preferable to insert a self-expanding metal stent designed for transgastric drainage.²⁷ A recent advance is the lumen-apposing design to reduce the risk of cyst content leaking into the lesser sac (Fig. 69-6).²⁸ These metal stents are removed endoscopically after pseudocyst resolution. Endoscopic transpapillary techniques include stenting the sphincter of Oddi to lower ductal pressures and to treat pancreatic ducts strictures. The stent can also be advanced via the pancreatic duct into the pseudocyst when there is a demonstrable communication.²⁹

These endoscopic methods are still evolving but have a reported success rates over 90% with experienced practitioners, in well selected patients. Caution needs to be exercised because of the risks of perforation, peritonitis, bleeding, and infection. The risk of bleeding is significantly reduced when the initial puncture is guided by EUS.

Open Surgical Treatment

There is no single surgical procedure that is appropriate for all pseudocysts, and the rise of less invasive approaches has resulted in fewer operations being performed for more limited indications. Open surgery is now rarely required for a pseudocyst but may be used to manage complications from other interventions. As with other treatments, an important factor dictating the choice is available expertise and equipment.²⁴

In principle, drainage operations are preferred to resection because they preserve pancreatic function, are technically easier, and have a lower mortality rate. A D’Egidio type II pseudocyst with a mature wall is best treated by internal drainage, particularly when ductal disruption or stricture is present. Recurrence rates should be less than 5%, and mortality should be less than 2%. The pseudocyst can be drained into the stomach, the duodenum, or the jejunum. The choice of surgical procedure depends on the location of the pseudocyst and its relationship to these organs.

A cystogastrostomy is ideal when the pseudocyst is adherent to the posterior stomach and indenting it (Fig. 69-7). A longitudinal anterior gastrostomy is followed by the stepwise excision of a disk (∼2 cm diameter) of stomach with subjacent pseudocyst wall. The tissue is sent for frozen section in all cases to exclude cystic neoplasia. Sutures are placed in stages to reduce the risk of edge bleeding as the disk is excised. Prior confirmation of the location of the pseudocyst may be required by needle aspiration, although it is usually obvious. The stoma should be large enough to allow transgastric débridement of any necrotic tissue if the collection proves to be WON rather than a pseudocyst. The disadvantage of the cystogastrostomy is that it is not a dependent stoma, and may act as a sump that allows accumulation of gastric debris. An alternative is a Roux-en-Y cystojejunostomy (Fig. 69-8) which is particularly suited to drainage of pseudocysts arising from the body and tail of the pancreas, when it is not adherent to the stomach and when it is bulging through the left transverse mesocolon.

Combining internal drainage of a pseudocyst with a lateral pancreatojejunostomy should be considered in patients with chronic pancreatitis and a dilated pancreatic duct because it will improve outcome without increasing the risk of the procedure. The blind end of the Roux limb should be placed toward the tail of the pancreas because this allows the head of the pancreas to be drained and the bile duct to be bypassed using the same limb, if required.

Distal pancreatic resection has a role, particularly when the head of the pancreas is relatively preserved. An endoscopic retrograde pancreatogram will help to define the extent of optimal resection. If there is no pancreatic duct obstruction there are very low recurrence and fistula rates.

External surgical drainage of a pseudocyst has a very limited role in critically ill patients where radiological or endoscopic drainage is not technically feasible and the risk of a controlled external fistula is an acceptable outcome. Other rare indications for external drainage at the time of laparotomy include the control of an immature ruptured pseudocyst, and for some bleeding pseudocysts where there has been oversewing of the bleeding point. An external fistula may resolve more rapidly with placement of a transpapillary stent and with the adjunctive use of a long-acting somatostatin analogue.