Figure -3b In this transverse scan, the pancreatic duct (arrow) is seen as a tube rather than a single echogenic line: as long as the internal diameter does not exceed 2-2.5 mm and the walls are parallel, this is still considered normal. Note that the posterior wall of the stomach(open arrow) looks almost identical to the pancreatic duct; care must be taken not to confuse the two. a= aorta:v= inferior vena cava: s splenic vein; L= liver n acute pancreatitis comparison between the pancreas and liver will demonstrate a decrease in echogenicity of the pancreas. Whenever possible, it is preferable to compare the parenchymal textures on the sagittal scan; this prov ides views of hepatic and pancreatic parenchyma at equal dista nces from the transducer obviating differential atte nuation by interposed tissues. A caution here is that the hy perechoic liver (as in fatty inf iltration) will make the pancreas appear to be hy pecho ic giv ing the false impression of acute pancreatitis. It is important to assess hepa tic echogen icity (i.e. can the normal echoes a bout the portal triads be seen? is the rela tionship of hepatic and renal cortical echogenic ity mainta ined? )to ensure that it does represent a proper internal standard by which to judge the pancreatic texture A common finding with acute pancreatitis is the presence of small amounts of fluid in proximity to the pancreas, frequently in the lesser sac or elsewhere about the pancreas. These collectio ns of pancreatic fluid, rich in enzymes, are sa id to occur in some 40 of patients with acute pa ncreatitis; they resolve sponta neously in about 50 of cases. Those collections which persist for more than four weeks are considered pseudocysts, half of which may resolve spontaneous ly. Morphologic characteristics do not allow separation of transient peripancreatic fluid collections from pseudocysts except by their seria behavior, i.e. the persistence of pseu Pseudocysts Persistence of fluid collections in or about the pancreas or lesser sac heralds the development of a pseudocyst which, by def inition, is a collection of pancreatic fluid contained by a fibrous wall or capsule They vary in size from only 2-3 cm to 10-15 cm in diameter. Altho ugh they are most commonly found in the peripancreatic region or lesser sac, pseudocysts have been described in a variety of locations inc luding Gerota's fascia, the porta hepatis, and the mediastinum(Figure 9) Figure -9. A small, essentially simple pseudocyst is seen anterior to the distal body and tail of the pancreas(arrowheads) and posterior to the stomach(arrows denote both gastric walls) indicating that it lies within the lesser sac. Although pseudocysts may be found almost anywhere, this is the most common site Pancreatic pseudocysts frequently conta in gravity-dependent debris or irregular septations as a result of tissue necrosis or hemorrhage. The more extensive the internal echoes within a pseudocyst the great the chances of a superimposed inf ection(9). The distinction between a simple pancreatic pseudocyst and an inf ected pseudocyst (or pancreatic abscess) is not easily or conf identy made by ultrasound alone; ifFigure - 3b. In this transverse scan, the pancreatic duct (arrow) is seen as a tube rather than a single echogenic line; as long as the internal diameter does not exceed 2-2.5 mm and the walls are parallel, this is still considered normal. Note that the posterior wall of the stomach (open arrow) looks almost identical to the pancreatic duct; care must be taken not to confuse the two. A = aorta; v = inferior vena cava; s = splenic vein; L = liver. In acute pancreatitis comparison between the pancreas and liver will demonstrate a decrease in echogenicity of the pancreas. Whenever possible, it is preferable to compare the parenchymal textures on the sagittal scan; this provides views of hepatic and pancreatic parenchyma at equal distances f rom the transducer obviating differential attenuation by interposed tissues. A caution here is that the hyperechoic liver (as in fatty infiltration) will make the pancreas appear to be hypoechoic giving the false impression of acute pancreatitis. It is important to assess hepatic echogenicity (i.e. can the normal echoes about the portal triads be seen? is the relationship of hepatic and renal cortical echogenicity maintained?) to ensure that it does represent a proper internal standard by which to judge the pancreatic texture. A common finding with acute pancreatitis is the presence of small amounts of fluid in proximity to the pancreas, f requently in the lesser sac or elsewhere about the pancreas. These collections of pancreatic fluid, rich in enzymes, are said to occur in some 40 % of patients with acute pancreatitis; they resolve spontaneously in about 50 % of cases. Those collections which persist for more than four weeks are considered pseudocysts, half of which may resolve spontaneously. Morphologic characteristics do not allow separation of transient peripancreatic fluid collections from pseudocysts except by their serial behavior, i.e. the persistence of pseudocysts (8) . Pseudocysts Persistence of fluid collections in or about the pancreas or lesser sac heralds the development of a pseudocyst which, by definition, is a collection of pancreatic fluid contained by a fibrous wall or capsule. They vary in size from only 2-3 cm to 10-15 cm in diameter. Although they are most commonly found in the peripancreatic region or lesser sac, pseudocysts have been described in a variety of locations including Gerota's fascia, the porta hepatis, and the mediastinum (Figure 9) . Figure - 9. A small, essentially simple, pseudocyst is seen anterior to the distal body and tail of the pancreas (arrowheads) and posterior to the stomach (arrows denote both gastric walls) indicating that it lies within the lesser sac. Although pseudocysts may be found almost anywhere, this is the most common site. Pancreatic pseudocysts f requently contain gravity-dependent debris or irregular septations as a result of tissue necrosis or hemorrhage. The more extensive the internal echoes within a pseudocyst, the greater the chances of a superimposed infection (9) . The distinction between a simple pancreatic pseudocyst and an infected pseudocyst (or pancreatic abscess) is not easily or confidently made by ultrasound alone; if