Pancreatic Pseudocysts

A pancreatic pseudocyst is a localized collection of pancreatic secretions, surrounded by a wall of fibrous or granulation tissue, which arises as a result of acute or chronic pancreatitis, pancreatic trauma, or obstruction of the pancreatic duct by a neoplasm ( Fig. 4-1 and Fig. 4-2 ). Pseudocysts account for about 75% of cystic lesions of the pancreas. They are distinguished from other peripancreatic fluid collections (cystic neoplasms, congenital, parasitic, and extrapancreatic cysts) by their lack of an epithelial lining, the high concentration of pancreatic enzymes within the pseudocyst, and their formation at least 4 weeks after an episode of pancreatitis or pancreatic trauma ( Table 4-1 ). Pseudocysts are formed by the inflammatory response that occurs after extravasated pancreatic secretions are walled off by the surrounding structures. The capsule of the pseudocyst can be thin fibrous tissue, which can progressively thicken as the pseudocyst matures. Often, the liquid contents of the pseudocyst are gradually resorbed by the body, and the pseudocyst resolves, findings indicating that the communication between the pseudocyst and the pancreatic duct has closed. The persistence of a pseudocyst implies an ongoing communication with the pancreatic ductal system, whether or not the ductal system can be demonstrated radiographically or pathologically.

Terminology

Because pseudocysts may resemble other collections of fluid that may arise as a complication of acute pancreatitis, clear terminology is required to differentiate these different clinical entities. The International Symposium on Acute Pancreatitis, held in 1992, established consensus definitions for pseudocyst, acute fluid collection, and pancreatic abscess.

Acute fluid collections form early in the course of acute pancreatitis and lack a discrete wall of fibrous or granulation tissue ( Fig. 4-3 ). Acute fluid collections are common in patients with severe pancreatitis and occur in 30 to 50% of cases. f ' Most of these lesions regress spontaneously without specifically directed therapy or drainage. Most acute fluid collections do not represent a communication with the pancreatic duct. Instead, they are a serous or exudative reaction to pancreatic inflammation and trauma. A fluid collection that persists for more than 4 weeks, that is usually surrounded by a well-defined wall, and that may communicate with the pancreatic ductal system, is termed a pancreatic pseudocyst.

A pancreatic abscess is a circumscribed collection of purulent infected fluid, containing little or no necrotic material, that arises as a complication of acute pancreatitis or trauma. A pancreatic abscess typically occurs late in the course of severe acute pancreatitis, often 4 or more weeks after the onset of symptoms. Patients present with signs and symptoms of infection. The presence of a purulent exudate, a positive culture for bacteria or fungi, and little or no necrotic pancreatic material differentiate a pancreatic abscess from infected pancreatic necrosis, a catastrophic complication that often occurs earlier in the course of severe pancreatitis. This distinction is crucial because the mortality for infected pancreatic necrosis is double that of pancreatic abscess, and the specific therapy for each condition is markedly different. A pancreatic abscess may be treated with percutaneous drainage in many cases, whereas infected pancreatic necrosis typically requires operative d├ębridement.

Figure 4-1 A computed tomography scan of a patient with a pancreatic pseudocyst in the head of the pancreas. The patient had symptoms of abdominal pain and nausea. The gallbladder appears distended, although results of liver function tests were normal.

Figure 4-2 A computed tomography scan of a patient with a large retrogastric pancreatic pseudocyst. The patient had symptoms of abdominal pain, back pain, nausea, and early satiety.

TABLE 4-1 -- Cystic Lesions of the Pancreas and Peripancreatic Region

Pancreatic pseudocyst

Pancreatic pseudopseudocyst (acute fluid collection) Pancreatic abscess

Cystic neoplasms of the pancreas Serous cystadenoma

Mucinous cystadenoma/cystadenocarcinoma Cystic islet cell tumor Acinar cell cystadenocarcinoma Cystic choriocarcinoma Cystic teratoma Parasitic cysts

Echinococcal cyst Taenia solium cyst Congenital cysts Simple cyst Polycystic disease

Isolated to pancreas

Associated with polycystic kidney disease Associated with von Hippel-Lindau disease Associated with cystic fibrosis Extrapancreatic cysts Duplication cyst Mesenteric cyst Splenic cyst Adrenal cyst

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