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

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)