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7 Pancreas Organ Boundaries Locate and identify the pancreas. Demonstrate the entire pancreas. The pancreas is located in the retroperitoneum, bounded on each side by the duodenum and the spleen. It lies transversely in the epigastrium, its axis directed at a slight angle from lower right to upper left. Locating the pancreas Barriers to scanning The pancreas is often difficult to locate because of its posterior position. The main barrier to scanning the pancreas is gas in the stomach and bowel (Fig. 7.1). Optimizing the scanning conditions fig. 7.1 The pancreas is obscured by the colon (Co), antrum (An), and costal arch (Ri). The pancreas, like the gallbladder, is best examined in the fasted patient. In some cases, visualization can be significantly improved by giving the patient an antigas medication. You can also apply local transducer pressure to push the gas aside. Of course, this should be done only after the other organs have been examined. Vision can be substantially improved by filling the stomach with water (500 ml, taken through a straw) (Fig. 7.2). Fig. 7.2 Locating the pancreas a Using the liver (L) as an acoustic window for locating the pancreas (P). An = antrum, Co = colon. b Scanning through the fluid-filled antrum (An). Co = colon. Organ identification More than with other upper abdominal organs, identification of the pancreas relies on the use of landmarks. Your principal landmarks are the aorta and the splenic vein (Figs. 7.3-7.5). Position the transducer for a high upper abdominal transverse scan, and angle the scan slightly upward into the liver. Identify the aorta and vena cava. Now move the scan plane caudally in small increments. In some cases you will have to repeat this pass several times and use both sliding and angling movements of the probe to scan around gas in the stomach and bowel. As you scan down the aorta, look for the landmarks shown in (Figs. 7.3 and 7.4). Fig. 7.3 Aorta (A) and celiac trunk (Tr). When you see this pattern in the transverse scan, you will find the pancreas at a slightly more caudal level. 136 Fig. 7.4 Aorta (A) plus a transverse section of the superior mesenteric artery (Ams) and a longitudinal section of the splenic vein (VI). When you see this pattern, you will almost always have the pancreas on the monitor. It appears as a gently curved structure passing anterior to the splenic vein. The ability to define the pancreas and delineate it from its surroundings will vary greatly from case to case. b Demonstrate the aorta (A). c Locate the celiac trunk (->). d Identify the splenic vein ( pancreas anterior to it ( ) and the ). Difficulties in identifying the pancreas The series of images shown above were obtained under ideal scanning conditions. In most examinations, however, the conditions will be less than ideal and often the pancreas cannot be completely visualized (Figs. 7.6-7.8). Fig. 7.6 Poor visualization of the pancreas ( ) due to obesity and overlying gas. Fig. 7.7 Obesity and pancreatic lipomaFig. 7.8 The pancreas is completely tosis. The superior mesenteric artery ( ) obscured by gas. and splenic vein (<-) are plainly seen, but the pancreas ( ) is poorly delineated. 137 Imaging the entire pancreas Below you will learn a systematic method of imaging the pancreas using parallel upper abdominal transverse and longitudinal scans. The tail of the pancreas can also be visualized by scanning through the spleen. This approach is described further under Anatomical Relationships (p. 150). Defining the pancreas in upper abdominal transverse scans KEY POINTS Multiple transverse and longitudinal scans are needed to survey the pancreas because of its length (approximately 15 cm). The tail of the pancreas can be scanned through the spleen. The splenic vein is the landmark for locating the pancreas in the transverse scan. Fig. 7.9 Due to the length of the pancreas, several passes are needed to survey the entire organ in transverse sections (Figs. 7.9,7.10). Obtain a longitudinal section of the pancreas anterior to the splenic vein (Figs. 7.9 b, 7.10 b). Notice the gently curved shape of the pancreas above the landmark. Sweep through this section several times. Then slide the transducer toward the tail of the pancreas, i.e., upward and to the left (Figs. 7.9 c, 7.10 c). Observe how the shape of the pancreas changes. You will notice that vision becomes poorer as the scan moves to the left. Scan through the tail of the pancreas. Its shape is highly variable. Now return to the starting point, and move the transducer to the right toward the head of the pancreas (Figs. 7.9 d, 7.10 a). Again, observe the change in shape. Sweep through the head of the pancreas several times. While the body and tail of the pancreas have a relatively smooth, elliptical shape in the transverse scan, the contour of the head shows irregular depressions at several sites. Surveying the pancreas in upper abdominal transverse scans a In each of these positions, the transducer is angled slightly upward and downward to sweep through the entire pancreas. The sections seen at these positions are shown in b-d. b Transverse midbody scan of the pancreas. From above downward you see the pancreas (P), splenic vein (VI), superior mesenteric artery (Ams), and aorta (A). 138 c Moving the transducer upward and to the left displays a section of the pancreatic tail (Pt). Notice that the tail extends well posteriorly and is thicker than the body of the pancreas. d Moving the transducer downward and to the right from the starting point displays a section of the pancreatic head (Ph) with the vena cava (Vc) behind it. The head is impressed medially by the confluence of the superior mesenteric and splenic veins (c). Fig. 7.10 Defining the pancreas in upper abdominal transverse scans a Typical appearance of the pancreatic head (Ph) above the vena cava (Vc). A = aorta, superior mesenteric artery ( ). b The transducer was moved slightly left to the midabdomen. You see the slender body of the pancreas ( ) lying anterior to the splenic vein (VI). c The transducer was moved farther cephalad and to the left. You see the tail of the pancreas with its marked posterior extension (<- ->). Defining the pancreas in upper abdominal longitudinal scans KEY POINT The aorta, celiac trunk, superior mesenteric artery, and splenic vein are the landmarks for identifying the pancreas in the longitudinal scan. Fig. 7.11 Start with the probe placed transversely on the upper abdomen, and define the body of the pancreas. While watching the screen, rotate the transducer to a longitudinal scan over the epigastrium. Keep the section of the pancreas in view, and angle the transducer slightly to locate the aorta. It will provide an aid to orientation. The key landmarks for locating the pancreas in the upper abdominal longitudinal scan are the aorta, celiac trunk, superior mesenteric artery, and splenic vein (Fig. 7.11 a). Concentrate on the pancreas. Scanned longitudinally, the pancreas presents a flat, oblong cross section. Move the transducer to the left in parallel steps. As you saw before, vision is increasingly degraded by gas as you scan into the left upper abdomen. Nevertheless, try to make out the shape of the pancreatic tail. As you noticed in the previous series of upper abdominal transverse scans (which gave longitudinal views of the pancreas), the thickness of the organ increases in the tail region (Fig. 7.11 b). Now return to the aorta and scan past it toward the right side. Notice that, while the portion of the pancreas over the aorta is flat but is still broad craniocaudally, as you move to the right the cross section of the pancreas thickens considerably, showing that you have reached the head (Fig. 7.11 c). Surveying the pancreas in upper abdominal longitudinal scans a Longitudinal landmarks for the pancreas (P) are the aorta (A), celiac trunk (Tr), superior mesenteric artery (Ams), and splenic vein (VI). 6 Moving to the left displays a section of the pancreatic tail (Pt). c Moving right displays a section of the pancreatic head (Ph). 139 Repeat this tail-to-head pass several times. Gain a clear spatial impression of the anatomy and location of the pancreas by observing how its cross section changes with transducer position (Fig. 7.12). - fig. 7.12 Defining the pancreas in upper abdominal longitudinal scans a Section of the pancreatic head (-> <-) anterior to the vena cava (Vc). Ard = right renal artery. b The transducer was moved left to the upper midabdomen, displaying a section of the pancreas (P) with its landmarks, the aorta (A), superior mesenteric artery (Ams), and splenic vein ( ). Note the craniocaudal extent of the pancreas. c The transducer was moved farther to the left. The thick tail of the pancreas (—> <-) is appreciated at this level. Scanning the tail of the pancreas through the spleen This approach is described fully in the section on Anatomical Relationships (p. 150). Variable shape of the pancreas The shape of the pancreas is variable. Typically it resembles a dumbbell. Sausage and tadpole shapes are also seen (Fig. 7.13). Fig. 7.13 Variants in the shape of the pancreas a Sausage shape. 140 b Tadpole shape. Organ Details Evaluate the echo pattern of the pancreas. Identify the pancreatic duct. Identify the common bile duct. Determine the size of the pancreas. Fig. 7.14 Cross anatomy of the pancreas. D = duodenum, P = pancreas, Dch = common bile duct, Dp = pancreatic duct, Dpa = accessory pancreatic duct. KEY POINT The parenchyma of the pancreas in young, slender individuals has about the same echogenicity as the liver parenchyma. Fig. 7.75 Normal pancreas (-><-). Normal pancreatic tissue has about the same echogenicity as the liver. The pancreas is very rich in parenchyma (pancreas = "all flesh") and has few definable internal structures. The pancreatic duct runs longitudinally through the parenchyma from tail to head, turning downward and backward at the head before joining the common bile duct and opening into the duodenum (Fig. 7.14). Ultrasound cannot define the side branches of the duct or an accessory pancreatic duct, if present. Pancreatic parenchyma The parenchyma in young, slender individuals has a uniform, granular echo texture with approximately the same reflectivity as the liver (Fig. 7.15). Its echogenicity is variable, however. It is lower in slender individuals and often increases markedly with ageing and with weight gain (Figs. 7.16, 7.17). The pancreas then appears as a bright streak lying superficial to the dark splenic vein. Fig. 7.16 Normal pancreas ( ) in an elderly subject. The tissue is relatively echogenic. Fig. 7.17 Elderly obese subject. The pancreas (-> <-) is normal and relatively echogenic. 141 Abnormalities of the pancreatic parenchyma Fibrolipomatosis. The most common abnormal finding is a homogeneous increase in parenchymal echogenicity due to fatty infiltration in obesity (Figs. 7.18, 7.19). This condition requires differentiation from a coarse "saltand-pepper" pattern, which is a normal variant (Fig. 7.20). Fig. 7.18 Pancreatic lipomatosis ( in a healthy subject. Table 7.1 Sonographic features of chronic pancreatitis Enlargement of the pancreas Internal structure coarse and heterogeneous ) Fig. 7.19 Pancreatic lipomatosis due to alcohol abuse ( ). This patient had no known pancreatic disease. Fig. 7.20 Healthy pancreas, showing a coarse salt-and-pepper echo pattern ( ). Chronic pancreatitis. Chronic pancreatitis is characterized by a coarse, heterogeneous echo pattern of increased density. The changes may be relatively minor (Fig. 7.21) or may present as coarse calcifications (Figs. 7.22, 7.23). The ultrasound features of chronic pancreatitis are listed in Table 7.1. Calcifications Pseudocysts Pancreatic duct dilated Indistinct contours Fig. 7.21 Chronic pancreatitis. Stippled calcifications ( ). 142 Fig. 7.22 Prominent calcifications, some very coarse ( ), in chronic pancreatitis. Fig. 7.23 Chronic pancreatitis. Conspicuous calcifications ( ). Table 7.2 Sonographic features of acute pancreatitis Enlargement of the pancreas - diffuse - circumscribed Acute pancreatitis. Acute pancreatitis leads to homogeneous, hypoechoic swelling of the organ (Figs. 7.24, 7.25). The swelling may be circumscribed or may involve the entire pancreas. There may also be areas of intrapancreatic hemorrhage and necrosis leading to circumscribed, echo-free lesions. Table 7.2 reviews the sonographic features of acute pancreatitis. Table 7.3 shows findings that may be seen in association with acute pancreatitis. Internal structure heterogeneous, rarefied, hypoechoic Indistinct contours Table 7.3 Associated findings in acute pancreatitis Ileus Ascites Necrotic tracks Abscess formation Bile duct dilatation Pleural effusion Fig. 7.24 Acute pancreatitis. Swelling and irregular contours ( Fig. 7.25 Acute pancreatitis ( ). ). Pseudocysts. Pseudocysts may develop as a complication of acute pancreatitis several weeks after the onset of the disease. Usually these lesions are easy to identify with ultrasound (Figs. 7.26-7.28). Fig. 7.26 Large pseudocysts ( secondary to acute pancreatitis. ) Fig. 7.27 Pseudocyst ( ) in the head of the pancreas. The patient had a history of acute pancreatitis. Gb = gallbladder, Vc = vena cava. Fig. 7.28 Very large pseudocyst ( following acute pancreatitis. S = stomach, P = pancreas. ) 143 Pancreatic carcinoma. Pancreatic carcinoma most commonly arises in the head of the pancreas. It appears sonographically as a nonhomogeneous, hypoechoic mass. Dilatation of the pancreatic duct is another common finding (see p. 145 and Fig. 7.29). It can be very difficult to appreciate a large pancreatic carcinoma due to poor delineation of the pancreas, destruction of the normal architecture, and intervening gas (Figs. 7.30-7.32). Table 7.4 lists the sonographic features of pancreatic carcinoma. Table 7.4 Sonographic features of pancreatic carcinoma Irregular contours Hypoechoic mass Dilated pancreatic duct Infiltration or displacement of surroundings 144 Fig. 7.29 Pancreatic carcinoma ( ) with dilatation of the pancreatic duct ( ). Fig. 7.30 Carcinoma of the pancreatic head ( ). Tr = celiac trunk. Fig. 7.31 Carcinoma of the pancreatic head ( ). The tumor is 8 cm in diameter. Ultrasound shows only a large, nonhomogeneous, ill-defined mass in the pancreatic region. Fig. 7.32 Pancreatic carcinoma ( As in Fig. 7.37, there is only a vague impression of a partially liquid mass in the pancreatic region. ).