复旦大学上海医学院：《医学影像学》PPT教学课件_胰腺超声成像 Sonographic imaging of the pancreas.doc_大学文库

Sonographic imag ing of the pancreas can provide va luable information concern ing size, texture, masses, ductal dilata tion, and f luid collections in and about the organ as well as disease states in related orga which border or affect the pancreas. Cost portability, and absence of ionizing radiation are distinct advantages of ultrasound w hereas large amounts of bowel gas or obesity coup led with the inherent operator dependency of the technique may be considered limitations. Diagnostic and therapeutic interventional procedures under ultrasound guida nce are steadily gaining favor by virtue of speed, cost and general availability of the equipment TECHNIQUE The examination is generally begun with the patient supine. Curved or phased array or sector scanners are best suited to examination of the pancreas; linear arrays are generally cumbersome and do not fit well in the subcostal space. Frequencies of 3 to 5 MHz(and, more recently the broad band transducers of 5-2 MHz for example)are suitable depend ing upon the patient' s body habitus. Children and slender adults may be successf ully scanned with 7-5 MHz instruments. Transverse scans utilize the left lobe of the liver as much as possible as a window into the pancreatic bed, covering the retroperitoneum from well above the pancreas. Visualization of the abdominal aorta and inferior vena cava assures that adequate depth penetration has been attained to image the pancreas. Sagittal sca nn ing begins in the midline, identif ying the great vessels and proceeds to the rig ht until the right kidney is seen and left to the splenic hilum (or until the pancreas is obscured by gas in the stomach or colon) to ensure vis ualization of as much of the organ as possible. In both scan pla nes steady firm pressure gradually applied will frequently e liminate interposed bowel gas and allow pancreatic imaging; several minutes of scanning w ith compression mainta ined may be necessary. Additio nally having the patient drink 250-500 cc of water may replace stomach gas and prov ide a window into the pancreas. The semi-erect position may also prove useful. If the patient is in pa in, water ingestion with the semi-erect position may be most effective at the beginning of the examination to avoid excessive swallowing of air which frequently accompanies pain Placing the patient in a steep oblique pos ition with the right side down following water ingestion may well fill the second portion of the duodenum with fluid and provide excellent visualization of the contour of the head of the pancreas NORMAL ANATOMY The pancreas lies in the retroperitoneum in the anterior pararenal fascial space anterior to the aorta and inferior vena cava. More specif ically the pancreas is genera lly found at a level just below the take -off of the superior mesenteric artery (SMA); the SMa is surrounded by the brightly echogenic fat at the root of the mesentery and lies posterior to the body of the pancreas. The celiac axis takes off the aorta generally at the superior border of the gland. Anterior to the sMa and seen in its transverse course is the splenic vein forming the dorsal border of the pancreas from the splenic hilum to its conf luence with the superior mesenteric vein at the neck of the pancreas. At this point, the head and uncinate process of the pancreas actually wrap around the venous conf luence which forms the portal vein, and pancreatic tissue is seen both anterior and posterior to the vein. The superior mesenteric vessels are considered the markers of division between the head and body of the pancreas(Figure 1-3) Figure-1 Transverse view demonstrates pancreas(p) with a homogeneous texture, more echogenic than that of liver(L). The splenic vein(s) the dorsal border of the gland. Note that wraps around the conf luence of the splenic and superior mesenteric veins (on this scan coinciding with the"s")with the uncinate process lyi mesenteric artery (SMA), open arrow the gas-filled second portion of duodenum and the white a

Sonographic imaging of the pancreas can provide valuable information concerning size, texture, masses, ductal dilatation, and fluid collections in and about the organ as well as disease states in related organs which border or affect the pancreas. Cost, portability, and absence of ionizing radiation are distinct advantages of ultrasound whereas large amounts of bowel gas or obesity coupled with the inherent operator dependency of the technique may be considered limitations. Diagnostic and therapeutic interventional procedures under ultrasound guidance are steadily gaining favor by virtue of speed, cost and general availability of the equipment. TECHNIQUE The examination is generally begun with the patient supine. Curved or phased array or sector scanners are best suited to examination of the pancreas; linear arrays are generally cumbersome and do not fit well in the subcostal space. Frequencies of 3 to 5 MHz (and, more recently, the broad band transducers of 5 -2 MHz for example) are suitable depending upon the patient's body habitus. Children and slender adults may be successfully scanned with 7-5 MHz instruments. Transverse scans utilize the lef t lobe of the liver as much as possible as a window into the pancreatic bed, covering the retroperitoneum f rom well above the pancreas. Visualization of the abdominal aorta and inferior vena cava assures that adequate depth penetration has been attained to image the pancreas. Sagittal scanning begins in the midline, identifying the great vessels and proceeds to the rig ht until the right kidney is seen and lef t to the splenic hilum (or until the pancreas is obscured by gas in the stomach or colon) to ensure visualization of as much of the organ as possible.In both scan planes steady, firm pressure gradually applied will f requently eliminate interposed bowel gas and allow pancreatic imaging; several minutes of scanning with compression maintained may be necessary. Additionally, having the patient drink 250 -500 cc of water may replace stomach gas and provide a window into the pancreas. The semi-erect position may also prove useful. If the patient is in pain, water ingestion with the semi-erect position may be most effective at the beginning of the examination to avoid excessive swallowing of air which f requently accompanies pain. Placing the patient in a steep oblique position with the right side down following water ingestion may well fill the second portion of the duodenum with fluid and provide excellent visualization of the contour of the head of the pancreas NORMAL ANATOMY The pancreas lies in the retroperitoneum in the anterior pararenal fascial space anterior to the aorta and inferior vena cava. More specifically, the pancreas is generally found at a level just below the take -off of the superior mesenteric artery (SMA); the SMA is surrounded by the brightly echogenic fat at the root of the mesentery and lies posterior to the body of the pancreas. The celiac axis takes off the aorta generally at the superior border of the gland. Anterior to the SMA and seen in its transverse course is the splenic vein forming the dorsal border of the pancreas f rom the splenic hilum to its confluence with the superior mesenteric vein at the neck of the pancreas. At this point, the head and uncinate process of the pancreas actually wrap around the venous confluence which forms the portal vein, and pancreatic tissue is seen both anterior and posterior to the vein. The superior mesenteric vessels are considered the markers of division between the head and body of the pancreas (Figure1-3) . Figure - 1. Transverse view demonstrates pancreas (p) with a homogeneous texture, more echogenic than that of liver (L). The splenic vein (s) forms the dorsal border of the gland. Note that the pancreas actually wraps around the confluence of the splenic and superior mesenteric veins (on this scan coinciding with the "s") with the uncinate process lying posterior to the vein. Small arrowhead indicates the superior mesenteric artery (SMA), open arrow the gas-filled second portion of duodenum, and the white a

Figure -3 Sagittal scan demonstrates normal pancreatic tissue(arrows) anterior(head) and posterior (uncinate process)to the superior mesenteric vein(s. L=liver; st= stomach. The right margin of the pancreas is formed by the second portion of the duodenum(the C-loop); better visua liza tion of the head of the pancreas is provided by hav ing the patient drink 250-500 ml of water and positioning right side down to fill the C-loop with water, outlining the pancreatic head w ith the water-f illed bowel. This technique will prove particularly useful in patients in whom the collapsed duodenum may simulate a mass in the head of the pancreas. The tail of the pancreas, which is frequently somewhat more cephalad than the head (i.e. the long axis will of ten be oriented more along a 2 o'clock-8 o'clock line than simply horizontal (3 o'clock-9 o' clock) and lies in close approx imation to the hilum of the spleen Water in the stomach may facilitate visualization of the distal body and ta il; occasionally scanning from posteriorly throug h the left kidney and/or spleen may provide a window into the distal body and tail. anterior to the pancreas lies the lesser sac which, under normal circumstances is only a potential space and thus not visible, and the stomach, identif ied by th alternating hyper- and hy poecho ic layers of its mucosa and muscularis, respectively. The left lobe of the liver lies anterior to the stomach and is, per haps the s ingle most im portant factor in producing a window into the pancreatic bed even in obese patients(1) Within the substance of the pancreas several normal structures may be visualized and evaluated most readily on the transverse scans. In the posterior aspect of the head of the pancreas is seen a circular lucency representing the term ination of the common bile duct; it should measure no more than 10 mm in ternal diameter. A second, usually smaller cystic structure is seen contiguous with the anter ior margin of the neck of the pancreas; this is the end-on view of the gastroduodenal artery which can easily be identif ied as such with Doppler investigation A circular or ovoid lucency similar to the gastroduode nal artery may occasionally be seen in the distal body or tail of the pancreas. This represents a turn of the normally tortuous sple nic artery which may mimic a cyst within the pancreatic parenchyma. Color or spectral Doppler will easily identify this structure as a portion of the normal splenic artery The pancreatic duct may be seen as a single echogenic line within the gland occasionally the duct contains suff icient fluid to appear tubu lar with both echogenic walls imaged This is still considered normal so long as the internal diameter of the duct does not exceed 2-2.5 mm. a caveat here is the fact that the muscular layer of the posterior wall of the stomach may mimic the pancreatic duct in size, conf iguration and echogenicity motion may help to identify the gastric wall as such. The pancreatic duct will be bounded anter iorly and posterior ly by recogniza ble pancreatic tissue. Vis ua lization of the normal duct has been reported in up to 86 of normal subjects(4, 5)(see Figure 3 b) Pancreatic Measurements The normal size of the pancreas is a matter of some de bate. Most authors who provide measurements of the gland cons ider normal AP measurements of the head, neck body and tail to be in the range of 3. 5 am 2.0 cm, 2.5 cm and 2.5 cm, respectively. In actual practice, focal enlargement or localized change in texture carries much more signif icance than an aberrant measurement(2) Pancreatic Echogenicity The texture of the pancreas varies with age. In the inf ant and young child the g land may be hy poechoic

Figure - 3c. Sagittal scan demonstrates normal pancreatic tissue (arrows) anterior (head) and posterior (uncinate process) to the superior mesenteric vein (s). L = liver; st = stomach. The right margin of the pancreas is formed by the second portion of the duodenum (the C-loop); better visualization of the head of the pancreas is provided by having the patient drink 250 -500 ml of water and positioning right side down to fill the C-loop with water, outlining the pancreatic head with the water-filled bowel. This technique will prove particularly useful in patients in whom the collapsed duodenum may simulate a mass in the head of the pancreas. The tail of the pancreas, which is f requently somewhat more cephalad than the head (i.e. the long axis will of ten be oriented more along a 2 o'clock - 8 o'clock line than simply horizontal (3 o'clock - 9 o'clock) and lies in close approximation to the hilum of the spleen. Water in the stomach may facilitate visualization of the distal body and tail; occasionally, scanning f rom posteriorly through the lef t kidney and/or spleen may provide a window into the distal body and tail. Anterior to the pancreas lies the lesser sac which, under normal circumstances is only a potential space and thus not visible, and the stomach, identified by the alternating hyper- and hypoechoic layers of its mucosa and muscularis, respectively. The lef t lobe of the liver lies anterior to the stomach and is, perhaps, the single most important factor in producing a window into the pancreatic bed even in obese patients (1) . Within the substance of the pancreas several normal structures may be visualized and evaluated most readily on the transverse scans. In the posterior aspect of the head of the pancreas is seen a circular lucency representing the termination of the common bile duct; it should measure no more than 10 mm in internal diameter. A second, usually smaller cystic structure is seen contiguous with the anterior margin of the neck of the pancreas; this is the end-on view of the gastroduodenal artery which can easily be identified as such with Doppler investigation. A circular or ovoid lucency similar to the gastroduodenal artery may occasionally be seen in the distal body or tail of the pancreas. This represents a turn of the normally tortuous splenic artery which may mimic a cyst within the pancreatic parenchyma. Color or spectral Doppler will easily identify this structure as a portion of the normal splenic artery. The pancreatic duct may be seen as a single echogenic line within the gland; occasionally the duct contains sufficient fluid to appear tubular with both echogenic walls imaged. This is still considered normal so long as the internal diameter of the duct does not exceed 2-2.5 mm. A caveat here is the fact that the muscular layer of the posterior wall of the stomach may mimic the pancreatic duct in size, configuration and echogenicity; motion may help to identify the gastric wall as such. The pancreatic duct will be bounded anteriorly and posteriorly by recognizable pancreatic tissue. Visualization of the normal duct has been reported in up to 86 % of normal subjects (4, 5) (see Figure 3 b) . Pancreatic Measurements The normal size of the pancreas is a matter of some debate. Most authors who provide measurements of the gland consider normal AP measurements of the head, neck, body and tail to be in the range of 3.5 cm, 2.0 cm, 2.5 cm and 2.5 cm, respectively. In actual practice, focal enlargement or localized change in texture carries much more significance than an aberrant measurement (2) . Pancreatic Echogenicity The texture of the pancreas varies with age. In the infant and young child the gland may be hypoechoic

as compared with the normal liver. This is attributed to the preponderance of glandular tissue and relative paucity of both fat and fibrous elements( Figure 4) Figure -4. Transverse scan in a young child. Note that the normal size pancreas (p) appears less echogenic than the liver(L. Predominance of glandular tissue and paucity of fat and fibrous stroma at this age make this a normal finding. S= splenic vein; v= inferior vena cava arrow superior mesenteric artery In the adult, the echogenicity of the pancreas is taken to be normal if it is equal to or greater than that of the liver assuming of course that organ to be normal. Clear def inition of the collagen and fat in the portal triads coup led w ith he patic parenchyma which is slig htly more echogenic than the adjacent renal cortex is reasonable assurance that the liver can be used as a normal internal standard(Figure 5) Figure-5. The pancreas(p) appears somewhat hy poechoic as compared with the liver(). This is due to increased echogenicity of the liver(fatty inf iltration rather than edema of the pancreas which is normal in this patient. Arrow= normal pancreatic duct; a aorta; v= inferior vena cava At and beyond the f if th decade, replacement of glandular tissue w ith fat and fibrosis produces a diff use, homogeneo us increase in the echogenic ity of the pancreas; it is not uncommon for the pancreas to reach a level of echogenicity at which it is indistinguisha ble from the contiguous retroperitoneal fat. These changes are considered a product of normal aging and are not associated with pancreatic insufficiency (3)(Figure 6) Figure-6 The pancreas(p) in this elderly patient is markedly echogenic becoming essentially isoechoic with the fat at the root of the mesentery which surrounds the superior mesenteric artery(arrow) This is a consequence of replacement of glandular tissue with fat and represents a normal aging change. s= splenic vein; a =aorta;V inferior vena cava:L= liver PATHOLOGIC CONDITIONS Acute pancreatitis Acute inf lammation of the pancreas may result from alcohol abuse biliary tract disease, trauma, or familial predisposition. Generally the history will provide strong indications of the etiology but sonographic evaluation of the biliary tree is frequently requested to establish primary or secondary involvement (e.g. biliary tract obstruction by pseudocyst or inf lammatory mass)

as compared with the normal liver. This is attributed to the preponderance of glandular tissue and relative paucity of both fat and fibrous elements (Figure 4). Figure - 4. Transverse scan in a young child. Note that the normal size pancreas (p) appears less echogenic than the liver (L). Predominance of glandular tissue and paucity of fat and fibrous stroma at this age make this a normal finding. S = splenic vein; v = inferior vena cava; arrow = superior mesenteric artery. In the adult, the echogenicity of the pancreas is taken to be normal if it is equal to or greater than that of the liver assuming, of course, that organ to be normal. Clear definition of the collagen and fat in the portal triads coupled with hepatic parenchyma which is slightly more echogenic than the adjacent renal cortex is reasonable assurance that the liver can be used as a normal internal standard (Figure 5) . Figure - 5. The pancreas (p) appears somewhat hypoechoic as compared with the liver (L). This is due to increased echogenicity of the liver (fatty infiltration) rather than edema of the pancreas which is normal in this patient. Arrow = normal pancreatic duct; a = aorta; v = inferior vena cava. At and beyond the fif th decade, replacement of glandular tissue with fat and fibrosis produces a diffuse, homogeneous increase in the echogenicity of the pancreas; it is not uncommon for the pancreas to reach a level of echogenicity at which it is indistinguishable f rom the contiguous retroperitoneal fat. These changes are considered a product of normal aging and are not associated with pancreatic insuf ficiency (3) (Figure 6) . Figure - 6. The pancreas (p) in this elderly patient is markedly echogenic, becoming essentially isoechoic with the fat at the root of the mesentery which surrounds the superior mesenteric artery (arrow). This is a consequence of replacement of glandular tissue with fat and represents a normal aging change. S = splenic vein; a = aorta; v = inferior vena cava; L = liver. PATHOLOGIC CONDITIONS Acute pancreatitis Acute inflammation of the pancreas may result f rom alcohol abuse, biliary tract disease, trauma, or familial predisposition. Generally, the history will provide strong indications of the etiology but sonographic evaluation of the biliary tree is f requently requested to establish primary or secondary involvement (e.g. biliary tract obstruction by pseudocyst or inflammatory mass)

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; if

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. 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

he patient's condition suggests the possibility of infected pseudocyst/abscess formation, dia gnostic aspiration under sonograph ic guidance using a 22 gauge need le is a propr iate and readily accomplished Such an infected collection left undrained carries a mortality rate in excess of 50 %(10)(Figure 10) Figure 10a ps Transverse scan demonstrating a large pseudocyst(ps) containing scattered debris throughout. Both walls of the stomach(arrows)are well visualized immediately anterior to the pseudocyst indicating its location in the lesser sac. a aorta Figure 10b. A somewhat oblique view through the same pseudocyst: a 22 gauge needle(arrow)is in place to determine the presence or absence of superimposed infection Sonographic documentation of the presence of a peripancreatic fluid collection, presumably a pseudocy st for several weeks should serve as the indicator for surgical or percutaneous intervention. Five to six weeks is cons idered appropr iate because by that time the walls of the pseudocyst are relatively well-formed and the chances for spontaneous regression have diminis hed. Then, too, the poss ibility of superimposed complications such as bleeding infection, and spontaneous rupture begins to rise subs tantia lly Formation of pseudoaneurysms of vessels about the pancreas which may accompany pse udocyst formation can be detected with either color or spectral Doppler interrogation(11) Percutaneous intervention A multip lic ity of techniques and guidance modalities have been described in the approach to percuta neo us drainage of pancreatic pseudocysts and abscesses. CT is a frequently employed and effective method for placement of drainage tubes. The combined use of real-time ultrasound and fluoroscopy offers several attractive features. Ultrasound is cons iderably less costly and generally more wide ly and readily availa ble Then, too, ultrasound perm its continuous monitoring of the puncturing need le(or trochar-catheter dev ice) to insure its proper placement w ithin the fluid collection. The supplemental use of fluoroscopy to follow guide w ires and catheters dur ing the introduction process serves to min imize chances for kinking of wires or tubes. We have found the combined use of sonographic and f luoroscopic mon itor ing of fluid drainage to provide the most cost effective, rapid, and read ily available approach(8, 12-18). a multiplicity of techniques and guidance modalities have been described in the approach to per cutanea us drainage of pancreatic pse udocysts and abscesses. CT is a frequently employed and effective method for placement of drainage tubes. The combined use of real-time ultrasound and fluoroscopy offers several attractive features. Ultrasound is cons iderably less costly and generally more widely and readily available. Then, too

the patient's condition suggests the possibility of infected pseudocyst /abscess formation, diagnostic aspiration under sonographic guidance using a 22 gauge needle is appropriate and readily accomplished. Such an infected collection lef t undrained carries a mortality rate in excess of 50 % (10) (Figure 10) . Figure - 10a. Transverse scan demonstrating a large pseudocyst (ps) containing scattered debris throughout. Both walls of the stomach (arrows) are well visualized immediately anterior to the pseudocyst indicating its location in the lesser sac. a = aorta. Figure - 10b. A somewhat oblique view through the same pseudocyst; a 22 gauge needle (arrow) is in place to determine the presence or absence of superimposed infection. Sonographic documentation of the presence of a peripancreatic fluid collection, presumably a pseudocyst, for several weeks should serve as the indicator for surgical or percutaneous intervention. Five to six weeks is considered appropriate because by that time the walls of the pseudocyst are relatively well-formed and the chances for spontaneous regression have diminished. Then, too, the possibility of superimposed complications such as bleeding, infection, and spontaneous rupture begins to rise substantia lly. Formation of pseudoaneurysms of vessels about the pancreas which may accompany pseudocyst formation can be detected with either color or spectral Doppler interrogation (11) . Percutaneous intervention A multiplicity of techniques and guidance modalities have been described in the approach to percutaneous drainage of pancreatic pseudocysts and abscesses. CT is a frequently employed and effective method for placement of drainage tubes. The combined use of real-time ultrasound and fluoroscopy offers several attractive features. Ultrasound is considerably less costly and generally more widely and readily available. Then, too, ultrasound permits continuous monitoring of the puncturing needle (or trochar -catheter device) to insure its proper placement within the fluid collection. The supplemental use of fluoroscopy to follow guide wires and catheters during the introduction process serves to minimize chances for kinking of wires or tubes. We have found the combined use of sonographic and fluoroscopic monitoring of fluid drainage to provide the most cost ef fective, rapid, and readily available approach (8, 12-18). A multiplicity of techniques and guidance modalities have been described in the approach to per cutaneous drainage of pancreatic pseudocysts and abscesses. CT is a f requently employed and effective method for placement of drainage tubes. The combined use of real-time ultrasound and fluoroscopy offers several attractive features. Ultrasound is considerably less costly and generally more widely and readily available. Then, too

ultrasound perm its continuo us monitoring of the puncturing need le(or trochar-catheter dev ice) to insure its proper placement w ith in the fluid collection. The suppleme ntal use of fluoroscopy to follow guide wires and catheters during the introduction process serves to minim ize chances for kinking of wires or tubes. We have found the combined use of sonographic and fluoroscopic monitoring of fluid draina ge to provide the most cost effective, rapid, and readily available approach(8, 12-18 Chronic pancreatitis Recurrent bouts of acute pancreatitis will produce sonographically demonstrable signs of chronic inf lammation, inc luding irregular areas of increased echogen icity representing fibrosis and/or calcification The increase in echoge nic ity in chronic pancreatitis is patchy and heterogeneous in contrast to the norma homogene us increase in echotex ture of the pancreas which results from f atty replacement of glandular tissue. In chronic pancreatitis the gland is usually diminished in volume and often dif f icult to outline Pseudocyst formation has been reported in 25-60 of patients with chronic pancreatitis as wel (19)(Figure 11 Figure -11a Transverse scan of a patient w ith chron ic calcif ic pancreatitis. Multiple shadowing calculi (arrows) are seen distributed throughout the gland a aorta Figure- 11b Sagittal scan of the same pancreas seen in Figure 11a. In this view the conglomerate calcif ications produce a large area of shadowing arrowheads). The gland is outlined by short white arrows. a aorta Dilatation of the pancreatic duct may also be a result of chronic inf lammation; the dilatation is of ten described as irregular or string of beads as a consequence of alternating areas of dilatation and fibrotic stricture. This appearance is sometimes offered as a means by which to distinguish ductal dilatation secondary to inf lammation from the smooth, tubular ectas ia which results from neoplastic obstruction as with carcinoma of the ampulla of Vater. The two dangers in relying upon this distinction too heavily are first that the morpholog ic differentiation is not always suf f iciently clear to allow the diag nos is. Secondly patients with chronic pancreatitis may also develop neoplasms and the coexistence of chronic inf lammation and carcinoma is an ever-present possibility (Figure 12) With the production of fibrosis and calcif ication, chronic pancreatitis may produce a mass composed of inf lammatory tissue which may simulate a neoplasm and, in fact, if it arises in the head of the gland, result in obstruction of the biliary or pancreatic ducts(Figure 13)

ultrasound permits continuous monitoring of the puncturing needle (or trochar -catheter device) to insure its proper placement within the fluid collection. The supplemental use of fluoroscopy to follow guide wires and catheters during the introduction process serves to minimize chances for kinking of wires or tubes. We have found the combined use of sonographic and fluoroscopic monitoring of fluid drainage to provide the most cost ef fective, rapid, and readily available approach (8, 12-18) Chronic pancreatitis Recurrent bouts of acute pancreatitis will produce sonographically demonstrable signs of chronic inflammation, including irregular areas of increased echogenicity representing fibrosis and/or calcification. The increase in echogenicity in chronic pancreatitis is patchy and heterogeneous in contrast to the normal homogeneous increase in echotex ture of the pancreas which results f rom fatty replacement of glandular tissue. In chronic pancreatitis the gland is usually diminished in volume and of ten dif ficult to outline. Pseudocyst formation has been reported in 25- 60 % of patients with chronic pancreatitis as well (19) (Figure 11) . Figure - 11a. Transverse scan of a patient with chronic calcific pancreatitis. Multiple shadowing calculi (arrows) are seen distributed throughout the gland. a = aorta Figure - 11b. Sagittal scan of the same pancreas seen in Figure 11a. In this view the conglomerate calcifications produce a large area of shadowing (arrowheads). The gland is outlined by short white arrows. a = aorta Dilatation of the pancreatic duct may also be a result of chronic inflammation; the dilatation is of ten described as irregular or "string of beads" as a consequence of alternating areas of dilatation and fibrotic stricture. This appearance is sometimes of fered as a means by which to distinguish ductal dilatation secondary to inflammation f rom the smooth, tubular ectasia which results f rom neoplastic obstruction as with carcinoma of the ampulla of Vater. The two dangers in relying upon this distinction too heavily are first that the morphologic differentiation is not always suf ficiently clear to allow the diagnosis. Secondly, patients with chronic pancreatitis may also develop neoplasms and the coexistence of chronic inflammation and carcinoma is an ever-present possibility (Figure 12) . With the production of fibrosis and calcification, chronic pancreatitis may produce a mass composed of inflammatory tissue which may simulate a neoplasm and, in fact, if it arises in the head of the gland, result in obstruction of the biliary or pancreatic ducts (Figure 13)

Figure 13b Somewhat cephalad to the plane of Figure 12a, this scan shows a large pseudocyst(ps) with extensive calcif ication in the walls (arrows) Figure- 13c obliq ue view of same patient shows extens ion of the pseudocyst (ps) into the porta hepatis. This, in combination with the fibrotic mass in the pancreatic head, results in partial obstruction of the common bile duct (d.v= portal vein; L= liver Obstruction of the common bile duct has been reported in some 5-10 of patients with chronic pancreatitis. Such masses are uncommonly confined to the tail of the pancreas and focal enlargement here should raise the suspicion of a genuine neoplasm Cystic fibrosis is another chronic condition which may produce a diff use increase in pancreatic echogen icity accompan ied by an overall decrease in pancreatic size in children and young adults. Smal areas of cystic degeneration are sometimes encountered largely in the tail of the gland(20) Cysts Although the majority of cysts of the pancreas are acquired and most represent pseudocysts following pancreatitis, some true cysts (i.e. those with an epithe lial lining) do occur. Sing le true cysts are extremely uncommon and are identif ied in the new born period. Mu ltiple true cysts are almost always associated with syndromes known to produce cysts in multiple organs. True pancreatic cysts are encountered in approximately 10 %o of patients w ith a l dom inant (adult) polycystic kidney disease and at least 30 of those with von Hippel-Lindau disease(10, 21) Pancreatic neoplasms Any focal enlargement of the pancreas is to be viewed with suspicion. Although focal pancreatitis can frequently be disting uished from carcinoma on the basis of history(e. g. alcohol abuse, pain) or laboratory f indings(e.g. elevated serum amylase), the sonograhpic morphology does not allow the distinction Pancreatic carcinoma most of ten appears as a focal hy poechoic en largement of the gland, frequently w ith poorly def ined margins owing to inf iltration of the surrounding fat by the neoplasm. Distribution of carcinomas within the pancreas is generally held to be approximately 70 in the head, 15-20 %o in the body and 5% in the tail. Those in the head tend to present earlier as they produce clinical signs and symptoms, e. g. jaundice, while still relatively small Neop lasms in the body and ta il are most of ten greater than 2 cm in size at the time of detection (Figure 14)

Figure - 13b. Somewhat cephalad to the plane of Figure 12a, this scan shows a large pseudocyst (ps) with extensive calcification in the walls (arrows). Figure - 13c. Oblique view of same patient shows extension of the pseudocyst (ps) into the porta hepatis. This, in combination with the fibrotic mass in the pancreatic head, results in partial obstruction of the common bile duct (d). v = portal vein; L = liver Obstruction of the common bile duct has been reported in some 5-10 % of patients with chronic pancreatitis. Such masses are uncommonly confined to the tail of the pancreas and focal enlargement here should raise the suspicion of a genuine neoplasm. Cystic fibrosis is another chronic condition which may produce a diffuse increase in pancreatic echogenicity accompanied by an overall decrease in pancreatic size in children and young adults. Small areas of cystic degeneration are sometimes encountered, largely in the tail of the gland (20) . Cysts Although the majority of cysts of the pancreas are acquired and most represent pseudocysts following pancreatitis, some true cysts (i.e. those with an epithelial lining) do occur. Single true cysts are extremely uncommon and are identified in the newborn period. Multiple true cysts are almost always associated with syndromes known to produce cysts in multiple organs. True pancreatic cysts are encountered in approximately 10 % of patients with autosomal dominant (adult) polycystic kidney disease and at least 30 % of those with von Hippel-Lindau disease (10, 21) . Pancreatic neoplasms Any focal enlargement of the pancreas is to be viewed with suspicion. Although focal pancreatitis can frequently be distinguished f rom carcinoma on the basis of history (e.g. alcohol abuse, pain) or laboratory findings (e.g. elevated serum amylase), the sonograhpic morphology does not allow the distinction. Pancreatic carcinoma most of ten appears as a focal hypoechoic enlargement of the gland, f requently with poorly defined margins owing to infiltration of the surrounding fat by the neoplasm. Distribution of carcinomas within the pancreas is generally held to be approximately 70 % in the head, 15-20 % in the body and 5 % in the tail. Those in the head tend to present earlier as they produce clinical signs and symptoms, e.g. jaundice, while still relatively small. Neoplasms in the body and tail are most of ten greater than 2 cm in size at the time of detection (Figure 14)