Introduction
Background
Pancreatic pseudocysts are the most common cystic lesions of the pancreas, accounting for 75-80% of such masses. A pancreatic pseudocyst is a collection of amylase-rich, lipase-rich, and enterokinase-rich fluid. It is most frequently located in the lesser peritoneal sac in proximity to the pancreas. Large pseudocysts can extend into the paracolic gutters; pelvis; mediastinum; and, rarely, the neck or scrotum. Some pseudocysts in the pancreatic parenchyma are loculated. The most common etiologies for pancreatic pseudocysts include chronic pancreatitis, acute pancreatitis, and pancreatic trauma. In addition, pseudocysts are associated with pancreatic ductal obstruction and pancreatic neoplasms.
Pseudocystic fluid has electrolyte concentrations similar to those in plasma. In contrast, pseudocystic fluid has a high concentration of amylase, lipase, and enterokinases such as trypsin. These concentrations reflect the origin of the lesion from extravasated pancreatic exocrine secretions resulting from pancreatic ductal disruption. The pancreatic secretions incite an intense inflammatory response, which eventually leads to the development of a thick fibrous capsule surrounding the pancreatic fluid.
For the first 3-4 weeks, any fluid that is associated with an episode of acute pancreatitis is called an acute fluid collection. Typically, acute fluid collections do not have high amylase concentrations. They do not possess a thick fibrous capsule, and they usually have an irregular shape. They may or may not be associated with peripancreatic fat necrosis. These features are in contrast with those of pancreatic pseudocysts, which have high amylase concentrations, are surrounded by a thick fibrous capsule, and are oval or round. The reason for these differences is that acute fluid collections do not result from pancreatic ductal disruption and the subsequent leakage of pancreatic exocrine secretions.
Acute fluid collections represent an accumulation of transudative or exudative fluids from surrounding tissues in reaction to the episode of pancreatitis. An unusual form of pancreatitis called groove pancreatitis may result in an acute fluid collection or the formation of a pseudocyst between the pancreatic head and the duodenum
Not until the fluid collection has been present for 4 or more weeks is it called a pancreatic pseudocyst. By this time, the inflammatory process leads to encapsulation of the fluid collection by a rim of fibrous tissue that may contain some granulation tissue as well. The capsule usually is densely adherent to surrounding viscera such as the stomach or duodenum.
Note that the capsule of a pancreatic pseudocyst does not possess a true epithelial lining. This is a critical point in the differentiation of pancreatic pseudocysts from cystic neoplasms of the pancreas.
Pathophysiology
Pseudocysts most commonly result from an acute or chronic inflammatory process involving the pancreas. Pancreatic trauma also can result in pseudocyst formation. In this process, the common etiologic insult that causes leakage of pancreatic juice and pseudocyst formation is pancreatic ductal disruption.
In acute pancreatitis, the ductal disruption is secondary to necrosis of part of the pancreas and subsequent duct leakage. This finding led to use of the term postnecrotic pseudocyst for pseudocysts that appear in relation to an episode of acute pancreatitis.
Patients with chronic pancreatitis may have elevated pancreatic duct pressures resulting from strictures, ductal calculi, or other causes. This effect results in a small ductal disruption that frequently is retained within the parenchyma of the gland. The types of pseudocysts sometimes are called retention cysts.
In severe acute pancreatitis, necrosis of part of the gland frequently occurs. This leads to extravasation of enzyme-rich pancreatic secretions and their loculation in potential spaces, including the lesser peritoneal sac and anterior pararenal space. At this point, this mass of pancreatic secretions and reactive exudate is termed an acute fluid collection and is found in as many as 50% of patients with acute pancreatitis, according to Luque-de Leon and Sarr.1 Acute fluid collections may contain necrotic pancreatic tissue. These collections should be considered sterile necrosis.
Most acute fluid collections associated with acute pancreatitis resolve spontaneously. Some remain for longer than 4 weeks and become encased in a fibrous capsule. Those that persist for longer than 6 weeks may be followed conservatively if they are smaller than 6 cm in diameter. They still have an excellent chance of undergoing complete spontaneous resolution with a low morbidity rate. Pseudocysts that persist for more than 6 weeks and are 6 cm in diameter or larger have a low likelihood of complete spontaneous resolution and are associated with significant morbidity rates. These pseudocysts should be drained.
Chronic pancreatitis is the most common cause of pancreatic pseudocysts. Pancreatic ductal disruption may be present in patients with pseudocysts associated with chronic pancreatitis. The presentation of a pancreatic pseudocyst resulting from chronic pancreatitis is subtler than the presentation of acute pancreatitis. Patients with chronic pancreatitis frequently complain of vague abdominal pain or early satiety. Occasionally, nausea and vomiting are prominent components of the clinical picture. Gastrointestinal tract complaints can prompt the clinician to order abdominal ultrasonographic (US) studies or abdominal CT scans. These studies are highly sensitive for demonstration of pancreatic pseudocysts.
Confusion surrounding disparate terminologies and descriptions used to define acute fluid collections, pancreatic pseudocysts, and other peripancreatic fluid collections was addressed at the International Symposium on Acute Pancreatitis convened in Atlanta, Georgia, in 1992. Bradley reported the results of this symposium (Bradley, 1993).2 Some of the definitions produced by consensus at this meeting include the following:
- Acute fluid collections: An acute fluid collection occurs early in the course of acute pancreatitis. It is located in proximity to the gland or within it. An acute fluid collection has no epithelial lining or capsule composed of fibrous or granulation tissue.
- Pancreatic pseudocysts: A pancreatic pseudocyst is a fluid collection contained within a well-defined capsule of fibrous or granulation tissue or a combination of both. A pseudocyst does not possess an epithelial lining. Pseudocysts may develop in the setting of acute pancreatitis or chronic pancreatitis.
- Pancreatic cysts: A pancreatic cyst is an epithelial wall or capsule that contains a fluid collection. Included in this group are congenital cysts and cystic neoplasms such as mucinous cystic tumors or serous cystadenomas.
Frequency
United States
Pseudocysts are the most common complication associated with chronic pancreatitis. Morel and Rohner wrote that a pseudocyst is found in 40-70% of patients undergoing surgical therapy for chronic pancreatitis.3 The incidence of true pseudocyst formation after an episode of acute pancreatitis is lower and approximately 10%, according to Bradley et al (Bradley, 1979).4 Overall, approximately 10,000 pancreatic pseudocysts are reported annually in the United States.
International
Pancreatic pseudocysts are known worldwide. Their incidence is similar to that in the United States, based on the prevalence of pancreatitis in each country.
Mortality/Morbidity
- Morbidity: Most pancreatic pseudocysts resolve spontaneously. Most published reports describe spontaneous resolution rates of greater than 50%. Beebe and associates reported that 85% of the pseudocysts followed in their series resolved spontaneously.5
- Mortality: Death directly attributable to a pancreatic pseudocyst is rare. Death occurs most frequently when vessel erosion results in a pseudoaneurysm that ruptures and bleeds freely into the peritoneal cavity. Reported mortality rates in this situation are 40-80%. Surgical mortality rates for patients undergoing surgical drainage are 0-6%.
Race
No well-described racial predilection exists for the formation of pancreatic pseudocysts.
Sex
No data exist to prove a proclivity for pseudocyst formation on the basis of sex.
Age
As Cooperman highlighted, pancreatic pseudocysts can occur anywhere in the pancreas in persons of any age.6 Because the common etiologies for pseudocyst formation include pancreatitis due to gallstones or alcohol, most pseudocysts are detected in adults.
Anatomy
Thorough knowledge of the anatomy of the pancreas and surrounding structures is essential for proper evaluation of patients with pancreatic pseudocysts and for planning potential therapeutic interventions. By convention, the pancreas is divided into 4 parts: head, neck, body, and tail.
The head of the pancreas forms the right side of the gland. It is cradled within the C-loop created by the course of the second through fourth portions of the duodenum. Anteriorly, the head of the pancreas is covered partially along its superior surface by the first portion of the duodenum. The gastroduodenal artery courses along the anterior surface of the pancreas, in a cephalic-to-caudal direction, creating a groove or indentation in the anterior surface of the gland that describes the boundary between the head and neck of the pancreas. Other anterior relations of the pancreatic head include the omental bursa, the greater omentum, the transverse colon, and the transverse mesocolon.
Posteriorly, the head of the pancreas rests against the right crus of the diaphragm, and it overlies the inferior vena cava. The termini of the renal veins are also posteriorly related to the pancreatic head, as is the aorta. The uncinate process is a projection of the left caudal area of the head of the pancreas, which is insinuated between the aorta and the superior mesenteric vessels. The intrapancreatic portion of the common bile duct courses along the posterior surface of the pancreas, or it may be partially embedded in the gland.
Anteriorly, the neck of the pancreas is in contact with the pylorus and the lesser peritoneal sac or omental bursa. Anterior to the omental bursa is the posterior surface of the stomach. The posterior relations of the neck of the pancreas include the termini of the splenic and superior mesenteric veins and their confluence to form the portal vein. The aorta and, more deeply, the spinal column are also important posterior relations of the pancreatic neck.
The predominant anterior relation of the body of the pancreas is the lesser peritoneal sac or omental bursa. The superior edge of the transverse mesocolon is in continuity with the peritonealized surface of the body of the pancreas. The splenic vein courses along the posterior surface of the pancreatic body, and the inferior mesenteric vein may course cephalad posterior to the body to join the splenic vein. The body of the pancreas rests against the aorta and the takeoff of the superior mesenteric artery. Other posterior relations include the left kidney, left renal vessels, left adrenal gland, and left crus of the diaphragm. The ligament of Treitz, the first several centimeters of the jejunum, and the splenic flexure of the colon are inferiorly related to the body of the pancreas.
The tail of the pancreas is at the left end of the gland and extends in the lienorenal ligament to contact the spleen at the splenic hilum. Anteriorly, the omental bursa and the splenic flexure of the colon are related to the pancreatic tail. Posteriorly, the left kidney is found.
The normal pancreatic duct system consists of the major pancreatic duct of Wirsung and the minor pancreatic duct of Santorini. The duct of Wirsung drains exocrine secretions from the tail, body, neck, and most of the head of the pancreas. It approaches the common bile duct and may join it, but it more commonly drains through a separate orifice at the ampulla of Vater. The duct of Santorini is responsible for draining part of the pancreatic head. Its orifice is found in the duodenum just proximal to the ampulla of Vater.
The arterial blood supply to the pancreas is derived from 4 major sources:
- The anterior superior and posterior superior pancreaticoduodenal arteries are branches of the gastroduodenal artery.
- The anterior inferior and posterior inferior pancreaticoduodenal arteries are derived from the superior mesenteric artery.
- The splenic artery provides numerous branches to the pancreas during its course along the dorsal superior aspect of the gland.
- The gastroduodenal artery provides additional arterial blood to the pancreas via its retroduodenal branch
.
Pancreatic veins drain into the superior mesenteric and splenic veins, and the lymphatic drainage from the pancreas goes to the pancreaticoduodenal, pancreaticolienal, portal, and celiac lymph nodes.
The major relevance of these anatomic relations is that a pancreatic pseudocyst can adhere to one or more hollow viscera after forming in a potential space, most commonly the lesser peritoneal sac. Therapeutic options are dictated by the anatomy and can include cystgastrostomy, cystoduodenostomy, cystojejunostomy, or combinations of the three.
With the abundance of major vessels in the region, imagining how vascular complications related to pseudocysts can occur is not difficult. Complications include thrombosis; pseudoaneurysm formation; and rupture of vessels, most commonly the splenic artery or vein.
Presentation
Physical findings
Results of the physical examination vary. Patients can have tenderness to palpation in the epigastrium. Thorough physical examination elicits the presence of a palpable upper abdominal mass in approximately 50% of patients with pancreatic pseudocysts. Ongoing free intraperitoneal hemorrhage can be associated with abdominal pain and with signs of shock.
Acute fluid collections are common in patients with acute pancreatitis or exacerbations of chronic pancreatitis. Acute fluid collections are easily diagnosed by using abdominal CT, which has become a routine study in the evaluation of patients with pancreatitis. The vast majority of acute fluid collections resolve.
Clinical suspicion for the presence of a pancreatic pseudocyst usually is aroused first by the persistence of abdominal pain following resolution of pancreatitis. Abdominal pain that persists for longer than 3 weeks after recovery from pancreatitis is a presenting symptom in 80-90% of patients with pancreatic pseudocysts, according to Cohen and Prinz.7 The authors also described abdominal fullness, nausea and vomiting, and weight loss as occurring in 40-50% of patients with pseudocysts. If the cyst compresses or obstructs the common bile duct or the second portion of the duodenum, jaundice and pruritus may become part of the clinical constellation.
Involvement of the stomach can cause early satiety, nausea, and, occasionally, vomiting. Pseudocysts that compress the duodenum can cause nausea, vomiting, and varying degrees of biliary obstruction. Vague epigastric or upper-quadrant abdominal pain is a frequent complaint in all of these scenarios.
Prolonged studies of the natural history of pseudocysts are a rarity. Vitas and Sarr published a series in which 68 patients with pancreatic pseudocysts were followed. After 51 months, 63% of the patients were asymptomatic. Only 9% of the patients developed any of the complications described above.8
Complications
Among the important complications associated with pancreatic pseudocysts are infection, obstruction, perforation, hemorrhage, and thrombosis. The most common acute complication of pancreatic pseudocysts is infection, which is heralded clinically by the presence of fever; worsening abdominal pain; and, occasionally, systemic signs of sepsis such as tachycardia, tachypnea, and hypotension. Laboratory analysis frequently demonstrates leukocytosis.
Obstruction of the hollow viscera of the gastrointestinal tract is not uncommon with pseudocysts that have been present for a long time. The presentation is usually less dramatic, and complete obstruction is uncommon. The presentation depends on the location of the pseudocyst and the particular viscus it is compressing, although true differentiation based on the symptoms alone may be difficult because of protean manifestations.
Pseudocysts may erode one of several named vessels, leading to pseudoaneurysm formation. The vessel most commonly affected is the splenic artery. The gastroduodenal artery, pancreaticoduodenal arteries, gastroepiploic and gastric arteries, and others have been involved as well. Acute episodes of hemorrhage associated with rupture of a pseudoaneurysm may be limited and present with sudden severe abdominal pain.
Pseudocysts may compress vascular structures as well, most commonly veins, which can lead to thrombosis. The most frequently affected vessel is the splenic vein.
Preferred Examination
Abdominal CT is performed in virtually every patient presenting with clinically significant pancreatitis or abdominal trauma severe enough to result in pancreatic ductal disruption. Therefore, abdominal CT is commonly the initial radiologic examination used to identify an acute fluid collection related to pancreatic ductal disruption.
Once the diagnosis is made, screening patients for resolution of the fluid collection is acceptable by using abdominal US. However, if a mature pseudocyst forms and does not resolve, repeat CT scanning is advised before planned percutaneous, endoscopic, or surgical interventions.
Limitations of Techniques
Currently available CT scanners enable the identification of virtually all clinically significant pancreatic pseudocysts. The major limitation is the inability to differentiate pseudocysts from cystic neoplasms by using CT.
Differential Diagnoses
Pancreas, Mucinous Cystic Neoplasm
Pancreas, Serous Cystadenoma
Pancreatitis, Acute
Pancreatitis, Chronic
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Further Reading
Keywords
lesser sac fluid collection, acute fluid collection, internal pancreatic fistula, postnecrotic pseudocysts, retention cysts, pancreatic cysts, postnecrotic pseudocysts
