Pancreas Review PDF

CHAPTER 16 The Pancreas REVA ARNEZ CURRY AND BETTY BATES TEMPKIN OBJECTIVES List the gross anatomy of the pancreas. Explain the function of the pancreas. Draw the epigastric vessels that surround the pancreas. Draw the blood supply to the pancreas. Describe the scanning plane used and the sonograp...

CHAPTER 16 The Pancreas REVA ARNEZ CURRY AND BETTY BATES TEMPKIN OBJECTIVES List the gross anatomy of the pancreas. Explain the function of the pancreas. Draw the epigastric vessels that surround the pancreas. Draw the blood supply to the pancreas. Describe the scanning plane used and the sonographic appearance of the pancreas in axial views, using vascular landmarks and adjacent anatomy. Describe the scanning plane used and the sonographic appearance of the pancreas in longitudinal views, using vascular landmarks and adjacent anatomy. Describe the relationship of the pancreas, duodenum, and biliary system. KEY WORDS Acini Cells — Produce pancreatic juice that is composed of enzymes to help digest fats, proteins, carbohydrates, and nucleic acids. Alpha Cells — Cells that account for 15% to 20% of pancreatic endocrine tissue and produce the hormone glucagon. Ampulla of Vater — Dilatation in the second portion of the duodenum, where the common bile duct and pancreatic duct(s) enter to discharge substances that aid in the digestive process. Beta Cells — Constitute 60% to 70% of the pancreatic endocrine cells that produce insulin. Common Bile Duct (CBD) — Distal portion of the biliary tract that transports and then discharges bile (that was manufactured in the liver) into the duodenum as needed to aid the digestive process. Delta Cells — Cells that account for approximately 5% of pancreatic endocrine tissue that produces the hormone somatostatin. Duct of Santorini — Pancreatic accessory duct that enters the duodenum approximately 2 cm superior to the duct of Wirsung. Duct of Wirsung — Main pancreatic duct. Transports and discharges pancreatic juice into the duodenum through the ampulla of Vater to aid the digestive process. Endocrine — Produces and secretes hormones directly into the bloodstream with a ductal system. Epsilon Cells — Cells that account for less than 1% of pancreatic endocrine cells, and produce the hormone ghrelin, which may affect blood sugar regulation. Exocrine — Produces and transports pancreatic juice via ducts to aid in digestion. Gamma Cells — Pancreatic Polypeptide (Pp) cells that comprise less than 5% of pancreatic endocrine cells and may affect blood sugar regulation. Gastroduodenal Artery — First branch of the common hepatic artery. Courses along the anterolateral aspect of the pancreas head just right lateral to the pancreas neck, where it divides into anterior and posterior superior pancreaticoduodenal branches. Supplies blood to the head of the pancreas and the duodenum. Glucagon — Hormone produced by alpha cells in the pancreas that causes the release of glucose to meet the immediate energy needs of the body. Insulin — Hormone produced by beta cells in the pancreas that causes glycogen formation from glucose in the liver. Islets of Langerhans — Groups of alpha, beta, and delta endocrine cells in the pancreas that produce insulin. Pancreatic Arcades — Vascular connections between the pancreaticoduodenal, hepatic, splenic, and superior mesenteric arteries that supply blood to the head of the pancreas. Pancreatic Body — Bordered right laterally by the pancreas neck, left laterally by the pancreas tail, anteriorly by the posterior wall of the stomach, and posteriorly by the splenic vein. Considered the largest portion of the pancreas. Pancreatic Head — Lies right lateral to the superior mesenteric vein; cradled in the C-loop of the duodenum; directly anterior to the inferior vena cava. Pancreatic Juice — Composed of enzymes produced by acini cells in the pancreas that help digest fats, proteins, carbohydrates, and nucleic acids. Pancreatic Neck — Situated between the pancreatic head and body immediately anterior to the superior mesenteric vein. At a slightly higher level, it lies anterior to the portal splenic confluence. Pancreatic Splenic Artery — Section of the artery located within the pancreas. Pancreatic Tail — Left lateral to the pancreas body and aorta and extends to the hilum of the spleen. Situated between the stomach anteriorly and left kidney posteriorly. The splenic vein runs along its posterosuperior surface. May lie higher, lower, or on an even level with the body. Pancreaticoduodenal Arteries — Arteries that supply the head of the pancreas and part of the duodenum with blood. Part of the pancreatic arcades (the vascular connections between the hepatic, splenic, and superior mesenteric arteries that also supply blood to the head of the pancreas). Continued 249 250 Section III ABDOMINAL SONOGRAPHY KEY WORDS—cont’d Portal Splenic Confluence — Area just posterior to the neck of the pancreas, where the splenic vein meets the superior mesenteric vein. Together, these veins form the portal vein. Portal Vein — Formed by the confluence of the splenic vein and superior mesenteric vein just posterior to the neck of the pancreas. Prehilar Splenic Artery — Section of the artery before it enters the hilum of the spleen. Prepancreatic Splenic Artery — Section of the artery before it leaves the pancreas. Somatostatin — Hormone produced by alpha cells in the pancreas that inhibits the production of insulin and glucose. Sphincter of Oddi — Muscle surrounding the ampulla of Vater that controls the flow of pancreatic juice from the pancreas and bile from the biliary tract into the duodenum. Splenic Artery — Supplies the body and tail of the pancreas with blood. From its origin at the celiac axis it runs along the superior edge of the pancreas body and tail parallel to the splenic vein. Splenic Vein — Along with tributaries of the superior mesenteric vein, serves as the venous drainage for the pancreas. Superior Mesenteric Vein — Along with tributaries of the splenic vein, serves as venous drainage for the pancreas. NORMAL MEASUREMENTS Anatomy Total length of pancreas AP measurement of head AP measurement of neck AP measurement of body AP measurement of tail Measurement 12 to 18 cm 2 to 3 cm 1.5 to 2.5 cm 2 to 3 cm 1 to 2 cm Tinteresting he pancreas has been and continues to be a most challenge to imaging using sonography. Its close relationship to the stomach, duodenum and proximal jejunum of the small intestine, transverse colon of the large intestine, and their contents may affect sound beam transmission and obscure pancreatic structures. This is especially true for patients who have been poorly prepped. Despite these obstacles, sonography has become useful for the evaluation and early detection of diseases of the pancreas. LOCATION The pancreas is descriptively divided into 5 parts: head, uncinate process, neck, body, and tail. When describing the location of the pancreas (Table 16-1), we move from the head and uncinate process on the right, through the neck and body, to the tail on the left. The pancreas is situated in the epigastrium and left hypochondrium. Position of the gland is variable, but it usually lies at the level of the first or second lumbar vertebra, extending from the C-loop of the duodenum to the splenic hilum. It lies horizontally across or anterior to the aorta and is shaped like an upside-down U (the ends of the U appear to have been pulled outward). The pancreas has also Suprapancreatic Splenic Artery — First 3-cm section of the artery as it originates from the celiac axis. Uncinate Process — Posteromedial projection of the pancreas head that lies directly posterior to the superior mesenteric vein and directly anterior to the inferior vena cava or in some cases, due to its size, the abdominal aorta. been described as dumbbell-, tadpole-, sausage-, and comma-shaped, with the head being the larger portion. Most of the pancreas is retroperitoneal; however, a small portion of the head is surrounded by peritoneum. Posterior to the pancreas are connective prevertebral tissue, the inferior vena cava, aorta, and diaphragm. Anterior to the pancreas are the stomach and transverse colon. The pancreas is closely related to the biliary tract and portal venous system. The main pancreatic duct, also called the duct of Wirsung, usually joins the common bile duct (see Chapter 15 for a description of the biliary tree) before both vessels enter the duodenum at the ampulla of Vater, a dilatation in the second portion of the duodenum (Figure 16-1). An accessory pancreatic duct, called the duct of Santorini, enters the duodenum approximately 2 cm superior to the duct of Wirsung. The portal splenic confluence is the area just posterior to the neck of the pancreas, where the splenic vein meets the superior mesenteric vein; together, these veins form the portal vein (Figure 16-2). The inferior mesenteric vein courses from inferior to superior as it drains the large intestine via several smaller branches. This vessel most often empties blood into the splenic vein; however, there is considerable variance regarding where the inferior mesenteric vein joins the portal system. SIZE The length of the pancreas ranges between 12 cm and 18 cm, or 6 to 8 inches. It is approximately 2.5 cm thick, 3 to 5 cm wide, and weighs between 60 g and 80 g. It is important to note the overall contour of the gland along with its size. Is the contour smooth, well defined, and without localized enlargement that appears to be out of place compared with the rest of the gland? This is important because a portion of the gland may be Chapter 16 Table 16-1 The Pancreas 251 Location of the Pancreas Head, Uncinate, Neck, Body, and Tail Routinely Visualized With Ultrasound Head Uncinate Process (variable size) Neck Body Tail Anterior to IVC, CBD IVC SMV, uncinate process Splenic vein, lt kidney Posterior to Peritoneum (except for small enclosed portion), superior duodenum (partially overlaps), GDA Duodenum C-loop SMV, pancreas neck, peritoneum Peritoneum, liver Splenic vein, SMA, lt renal vein, lt adrenal gland, aorta Stomach, liver, peritoneum (except for posterior surface) Liver, superior duodenum, CHA, PHA Duodenum C-loop, GDA, CBD Liver, superior duodenum, CHA, PHA Pancreas head Superior to Inferior to Medial to Liver, pylorus, CHA, PHA, portal vein Pancreas head, GDA Lt lateral to Rt lateral to SMV, uncinate process, splenic vein, pancreas neck, aorta SMA Duodenojejunal flexure (inferior surface) Celiac artery, splenic artery, CHA Stomach, splenic artery (portion[s]), lateral lt lobe liver, bowel portion Liver lt lateral lobe Pancreas tail Spleen Pancreas neck, GDA, SMV Lt renal artery, lt renal vein, SMA, aorta, pancreas body Pancreas body CBD, Common bile duct; CHA, common hepatic artery; GDA, gastroduodenal artery; IVC, inferior vena cava; PHA, proper hepatic artery; SMA, superior mesenteric artery; SMV, superior mesenteric vein; UP, uncinate process. enlarged, yet it may actually be within normal limits. Therefore an assessment of glandular contour is essential when evaluating size. Anteroposterior measurements of the head, neck, body, and tail vary widely. The head ranges between 2 and 3 cm, although some heads sized at up to 4 cm have been noted. It has been questioned whether the uncinate process (a medial extension of the head) contributes to these wide ranges. The size of the neck is between 1.5 and 2.5 cm; the body is between 2 and 3 cm; and the tail is between 1 and 2 cm. According to one reference, the “top normal” measurements for the adult pancreas were 3 cm for the head, 1 cm for the neck, 2.2 cm for the body, and 2.8 cm for the tail. One study on pancreatic imaging showed that the most reliable measurements of the head, body, and tail were taken in the morning after overnight fasting, as opposed to taking measurements after the patient had eaten and/or later in the day. Figure 16-3 shows the correct caliper placement to measure each segment of the pancreas. Note how the epigastric vessels serve as distinctive landmarks. The splenic vein should be seen in its entirety to accurately measure the tail. As with many abdominal organs, the size of the pancreas gland normally decreases with age. GROSS ANATOMY Head The pancreatic head lies to the right of the superior mesenteric vein. It is cradled in the C-loop of the duodenum, directly anterior to the inferior vena cava. Two vessels may be identified at the head of the pancreas: the common bile duct along the posterolateral portion and the gastroduodenal artery anterolaterally. The common bile duct (CBD) is the distal portion of the biliary tract that courses inferomedially from the level of the gallbladder neck, running posterior to the first part of the duodenum and then either passing directly through the pancreatic head or running along a groove on its posterolateral surface to meet with the main pancreatic duct. Joined together or separately, the ducts enter the duodenum at the ampulla of Vater (see Figure 16-1). The common bile duct transports and then discharges bile (manufactured in the liver) into the duodenum as needed to aid the digestive process. The gastroduodenal artery is the first branch of the common hepatic artery, which originates from the celiac axis. It courses along the anterolateral aspect of the pancreas head just right lateral to the pancreas neck, where it divides into the anterior and posterior 252 Section III ABDOMINAL SONOGRAPHY Right hepatic duct Left hepatic duct Gallbladder Common hepatic duct Common bile duct (supraduodenal portion) Cystic duct (Retroduodenal portion) Duct of Santorini (accessory duct) (Retropancreatic portion) Pancreas Duct of Wirsung C-loop of duodenum FIGURE 16-1 Relationship of the Pancreas, Duodenum, and Biliary System. Note that the head of the pancreas is partially surrounded by the C-loop of the duodenum. The union of the main pancreatic duct and distal common bile duct is illustrated. Superior mesenteric vein Neck Head Neck Body Head ∗ ∗ Body ∗ ∗ Inferior vena cava Splenic vein Spine Inferior vena cava Tail Aorta FIGURE 16-2 Portal splenic confluence. superior pancreaticoduodenal branches. It supplies blood to the head of the pancreas and the duodenum (Figure 16-4). The uncinate process is a posteromedial projection of the pancreas head that lies directly posterior to the superior mesenteric vein and directly anterior to the inferior vena cava or in some cases, due to its size, the aorta. ∗Tail ∗ ∗ Portal/splenic confluence Superior mesenteric artery ∗ Aorta Superior mesenteric artery FIGURE 16-3 Anteroposterior Measurement of the Pancreas. Correct caliper placement for measuring the anteroposterior dimension of the head, neck, body, and tail of the pancreas. One way to visualize this area is to draw an imaginary line from the middle of the portal splenic confluence to the middle of the inferior vena cava on a transverse image of the mid epigastrium. The tissue located to the right of the imaginary line is most likely the uncinate process (Figure 16-5). Neck Structurally, the pancreatic neck is located between the pancreatic head and body. It is situated immediately Chapter 16 Left gastric artery Common hepatic artery Splenic artery Proper hepatic artery Superior mesenteric artery Gastroduodenal artery Aorta FIGURE 16-4 Celiac Axis and Branches. Note the gastroduodenal artery as it courses inferiorly to the first branch of the proper hepatic artery. Pancreas neck Imaginary line Inferior vena cava Superior mesenteric artery * * * 253 Tail Celiac axis Portal/splenic confluence The Pancreas Uncinate process Aorta FIGURE 16-5 Uncinate Process. A line drawn from the middle of the portal splenic confluence to the middle of the inferior vena cava to locate the uncinate process. anterior to the superior mesenteric vein; slightly superior to that level, it lies anterior to the portal splenic confluence. Some sonographers do not consider the neck to be an individual structure but, rather, include it as part of either the head or the body. Body The pancreatic body lies anterior to the aorta, superior mesenteric artery, and splenic vein. The splenic vein runs along the posterior superior surface of the body and tail, closely following the shape of the gland (see Figure 16-2). The pancreas body is bordered right laterally by the neck, left laterally by the tail (although it is not certain exactly where the body ends and the tail begins), and anteriorly by the posterior wall of the stomach. The body is considered the largest portion of the pancreas. The pancreatic tail lies left lateral to the pancreas body and aorta and extends to the hilum of the spleen. It is situated between the stomach anteriorly and left kidney posteriorly. The splenic vein runs along its posterosuperior surface. The tail may lie higher, lower, or on an even level with the body. VASCULAR ANATOMY The arterial supply of the pancreas includes blood from the pancreaticoduodenal arteries (branches of the gastroduodenal artery and superior mesenteric artery) and branches of the splenic artery. The superior and inferior pancreaticoduodenal arteries supply a portion of the duodenum and along with the pancreatic arcades—the vascular connections between the hepatic, splenic, and superior mesenteric arteries—supply the head of the pancreas. The pancreatic branches of the splenic artery supply the body and tail of the pancreas with blood. As it originates from the celiac axis, the splenic artery runs along the superior edge of the pancreas body and tail parallel to the splenic vein. The splenic artery is normally tortuous and can course anteriorly to the lateral portion of the tail. It descriptively consists of four sections (Figure 16-6): • Suprapancreatic: The first 3 cm of the splenic artery as it originates from the celiac axis. The dorsal pancreatic artery originates from this section. • Pancreatic: Within the pancreas. The pancreatic magna, or great artery, originates from this section. • Prepancreatic: Before it leaves the pancreas. The caudal pancreatic artery originates from prepancreatic or prehilar sections. • Prehilar: Before it enters the spleen. The venous drainage of the pancreas is through tributaries of the splenic vein and superior mesen­ teric vein. PHYSIOLOGY The pancreas is a (digestive exocrine) and (hormonal endocrine) gland. Approximately 90% of the gland is exocrine and 10% endocrine: Only 2% of the gland’s weight is composed of endocrine tissue. The exocrine function (via ducts) is carried out by the acini cells of the pancreas, which can produce up to 2 L of pancreatic juice per day. Acini cells resemble grape clusters, with small areas of endocrine tissue interspersed between. Pancreatic juice is composed of enzymes that help digest fats, proteins, carbohydrates, and nucleic acids. Pancreatic enzymes that aid in digestion include amylase, which digests carbohydrates; lipase, which digests fat; trypsin, chymotrypsin, and carboxypeptidase, which digest proteins; and nucleases, which digest nucleic acids. The largest component of 254 Section III ABDOMINAL SONOGRAPHY Common hepatic artery Left gastric artery Dorsal pancreatic artery Suprapancreatic artery Gastroduodenal artery Pancreatic artery Prepancreatic artery Caudal pancreatic artery Pancreatic magna artery Aorta Spleen Prehilar section FIGURE 16-6 Arterial Anatomy of the Pancreas. The suprapancreatic, pancreatic, prepancreatic, and prehilar sections of the splenic artery are shown. Note the origin of the dorsal pancreatic, pancreatic magna, and caudal pancreatic arteries from the splenic artery. Table 16-2 Components of Pancreatic Juice Components of Pancreatic Juice Enzyme Acts on Amylase Lipase Trypsin, chymotrypsin, carboxypeptidase Nucleases Sodium bicarbonate Carbohydrates Fats Proteins Nucleic acids Hydrochloric acid pancreatic juice is sodium bicarbonate, a substance needed to neutralize hydrochloric acid produced in the stomach. Cells lining the pancreatic duct produce bicarbonate (Table 16-2). Chyme (partially digested food) in the duodenum stimulates the release of hormones, which act on pancreatic juice formation. These hormones are cholecystokinin, gastrin, acetylcholine, and secretin. The first three stimulate acini cells to produce digestive enzymes; secretin stimulates production of sodium bicarbonate. Intercalated ducts drain pancreatic juice from the acini cells into intralobular connecting ducts and, finally, into the main pancreatic duct. Pancreatic juice moves into the duodenum through the main pancreatic duct, the duct of Wirsung, a vessel approximately 2 mm in diameter. In approximately 77% of cadavers, the duct of Wirsung meets the common bile duct before both ducts enter the duodenum through the ampulla of Vater. As previously mentioned, an accessory duct, the duct of Santorini is a normal variant that enters the duodenum approximately 2 cm superior to the main duct (see Figure 16-1). The sphincter of Oddi, a muscle surrounding the ampulla, relaxes to allow pancreatic juice (and, if the gallbladder has been stimulated, bile) to flow into the duodenum. The endocrine portion of the pancreas is located in the alpha, beta, delta, gamma, and epsilon cells in the islets of Langerhans. Beta cells comprise 60% to 70% of the endocrine cells and produce insulin, a hormone that causes glycogen formation from glucose in the liver. It also enables cells with insulin receptors to take up glucose. Hence, blood glucose level decreases. Alpha cells account for 15% to 20% of endocrine tissue and produce glucagon, a hormone that causes the opposite effect—cells release glucose to meet the immediate energy needs of the body. Glucagon also stimulates the liver to convert glycogen to glucose, thus increasing blood glucose levels. Delta cells constitute approximately 5% of endocrine tissue and produce a substance called somatostatin. This hormone inhibits the production of insulin and glucagon. Gamma cells secrete pancreatic polypeptide (PP) and comprise less than 5% of endocrine cells. Epsilon cells constitute less than 1% of endocrine tissue. The exact function of gamma and epsilon cells is not clearly understood. One research study on 24 human fetal pancreases documented the occasional product of PP and ghrelin together. Studies have documented the release of PP in hypoglycemia, when food is ingested and in response to “sham” eating, Chapter 16 Table 16-3 Endocrine Cells and Pancreatic Hormones Type of Cell Hormone Action Beta Alpha Delta Gamma Insulin Glucagon Somatostatin Pancreatic polypeptide Ghrelin Glucose → Glycogen Glycogen → Glucose Alpha/beta inhibitor Related to blood sugar regulation Related to blood sugar regulation Epsilon when food is chewed but not swallowed. Pancreatic hormones produced by alpha, beta, gamma, delta, and epsilon cells are released in minute quantities directly into the bloodstream (Table 16-3). SONOGRAPHIC APPEARANCE When evaluating the pancreas, the sonographer must examine the texture, contour, shape, and size of the gland. Echo texture of the normal pancreas varies and can appear homogeneous to heterogeneous depending on the amount of interlobular fat that is present. Generally the pancreas appears more echo-dense or hyper­ echoic compared to the appearance of the normal liver. The borders of the pancreas are usually well defined with a smooth, curvilinear contour. Shape and size of the pancreas were discussed earlier in the chapter. The main pancreatic duct (duct of Wirsung) is best seen longitudinally in a transverse scanning plane, within the central portion of the pancreas. Two thin reflective lines separated by about 2 mm of anechoic pancreatic juice may be visualized running the entire length of the pancreas, or only a section or two may be visible at one time depending on the exact orientation of the duct and whether the scanning plane is slightly obliqued. When identifying the duct, care must be taken not to confuse it with the splenic vein, splenic artery, or posterior stomach wall. The close proximity of these structures and similar sonographic appearance can make it a challenge to differentiate them from one another. If there is a question, the splenic vein can be differentiated by following the vessel to its portal vein junction. The splenic artery can be followed back to its origin at the celiac axis, and having the patient drink fluid (if not restricted) will distend the stomach, making it easily identifiable (it also serves to obliterate any view obscuring gas in the stomach as well as provides a clear sonic “window,” making imaging of the epigastrium easier). Transverse Scanning Plane Images Showing Longitudinal Pancreas The pancreas essentially transverses the abdomen, with the head on the right, the neck and body through the The Pancreas 255 midline, and the tail on the left. Therefore the long axis and other longitudinal sections of the pancreas are seen in transverse scanning plane images. Since the pancreas is surrounded by epigastric vessels (gastroduodenal artery, common bile duct, inferior vena cava, superior mesenteric vein, portal splenic confluence, portal vein, splenic vein, superior mesenteric artery, aorta), these vessels serve as excellent landmarks. Head (Inferior Vena Cava, Gastroduodenal Artery, Common Bile Duct) As previously noted, the head sits directly in front of (or anterior to) the inferior vena cava, and portions of the common bile duct and gastroduodenal artery run along the right lateral border of the head. The inferior vena cava appears just posterior to the head and uncinate process as a round or oval anechoic structure with thin, smooth walls. Depending on the breathing technique being used, the inferior vena cava can appear very wide or narrow. The common bile duct (seen posterolaterally) and the gastroduodenal artery (seen anterolaterally) appear as two small, anechoic structures with bright walls. As seen in Figure 16-7, longitudinal sections of the pancreas head and axial sections of the inferior vena cava, common bile duct, and gastroduodenal artery are visualized in transverse scanning plane images. Neck (Superior Mesenteric Vein, Portal Splenic Confluence, Inferior Vena Cava) As discussed, a portion of the superior mesenteric vein is directly posterior to the inferior level of the neck of the pancreas, and the portal splenic confluence (splenic vein joins the superior mesenteric vein to form the portal vein) is directly posterior to a more superior level of the neck. Just medial to the pancreas head, the neck and uncinate process are separated by the superior mesenteric vein. These vessels appear anechoic with reflective borders and are relatively easy to dif­ ferentiate because the confluence is larger. The gland is thinner at the neck and merges into the pancreas body (Figure 16-8). Body and Tail (Splenic Vein, Superior Mesenteric Artery, Aorta) The pancreas body is located anterior to the splenic vein, superior mesenteric artery, and aorta. It has been described as projecting more anteriorly than the other segments of the pancreas, thus serving as a shelf for the stomach (Figure 16-9). The splenic vein clearly denotes the body and tail of the pancreas and can be seen (coursing from the hilum of the spleen) closely following along the posterosuperior margin of the tail and body, to its confluence with the superior mesenteric vein (forming the portal vein) behind the neck of the Anterior Liver Gastroduodenal artery Left renal vein Neck Splenic vein Body Bowel Bowel shadow Head Common bile duct Right Left Inferior vena cava Right renal artery Superior mesenteric artery Spine Uncinate Process Tail Aorta Posterior Liver Anterior Superior Gastroduodenal mesenteric vein artery Neck Body Superior mesenteric artery Left Splenic vein Left renal vein Duodenum Right Head Common bile duct Inferior vena cava Right renal artery Spine Aorta Right crus of Left renal Uncinate diaphragm artery Process Refraction shadow Posterior Through transmission Anterior Gastroduodenal artery Head Neck Body Liver Duodenum Air/gas in duodenum Splenic vein Common bile duct Stomach Shadowing from air/gas Shadowing from air/gas Right Left Portal splenic confluence Inferior vena cava Right kidney Aorta Spine Right renal artery Left renal vein Tail Superior mesenteric artery Posterior FIGURE 16-7 Longitudinal Pancreas Head. Transverse scanning plane images of the midepigastrium highlighting longitudinal sections of the pancreas head. Note the appearance and proximity of surrounding structures. Observe the anechoic, axial sections of the common bile duct (posteriorly) and gastroduodenal artery (anteriorly) along the right lateral margin of the head. Anterior Neck Portal splenic confluence Stomach/ bowel Body Left Celiac artery Duodenum/ bowel Right Head Liver Aorta Spine A Inferior vena cava Right renal artery Left renal vein Posterior Superior mesenteric vein Duodenum/bowel Anterior Neck Body Superior mesenteric artery Liver Head Stomach Gallbladder Right Left Tail Aorta Left renal vein Spine B Inferior Uncinate Right renal vena cava process artery Posterior Anterior Portal splenic confluence Neck Duodenum bowel Right Liver Stomach Left Body Head Tail C Common bile duct (measurement) Inferior vena cava Posterior Spine Superior Aorta mesenteric artery FIGURE 16-8 Longitudinal Pancreas Neck. Mid-epigastric transverse scanning plane images highlighting longitudinal sections of the neck of the pancreas and associated adjacent structures. Notice how compact the anatomy is and how closely related the pancreas is to adjacent epigastric vessels, duodenum and bowel, and the stomach. A is the level where the portal splenic confluence is directly posterior to the neck. In B, a level slightly inferior to the level in A, observe how the uncinate process is always present when the superior mesenteric vein is visualized. This is the level where the superior mesenteric vein is sandwiched between the neck (anteriorly) and uncinate (posteriorly). In C, the neck is easy identifiable just anterior to the portal splenic confluence. Note the calipers indicating the common bile duct measurement, and observe how the pancreas serves as a shelf for the stomach (seen anteriorly). 258 Section III ABDOMINAL SONOGRAPHY Superior mesenteric artery Body Neck Portal splenic confluence Head Anterior Fluid filled stomach Wirsung’s duct Liver Right Left Inferior vena cava A Right kidney Head Tail Spine Right renal artery Neck Aorta Posterior Anterior Left kidney Left renal artery Body Fluid filled duodenum Liver Right Left Fluid and gas filled stomach Posterior through transmission Posterior through transmission B Aorta Posterior Left Inferior renal vena cava vein Superior mesenteric artery Tail Splenic vein FIGURE 16-9 Longitudinal Pancreas Body. A, B, and C are transverse scanning plane images of the mid-epigastrium, highlighting longitudinal sections of the pancreas body. Notice how the body lies anterior to, and in the same plane with, the aorta and superior mesenteric artery, medial to the neck and tail, and posterior to the stomach and liver. In A, observe the anechoic, longitudinal section of Wirsung’s duct (main pancreatic duct) in the central portion of the body and part of the tail. Also notice how the fluid-filled stomach helps to delineate the anterior margins of the body and tail. Parts B and C (located on the next page) clearly demonstrate how the splenic vein runs along the posterior surface of the body. pancreas. The splenic vein presents with bright walls and anechoic lumen (Figures 16-10 and 16-11). aorta) serve as excellent landmarks for identifying the pancreas. Sagittal Scanning Plane Images Showing Axial Pancreas Head (Inferior Vena Cava, Gastroduodenal Artery, Common Bile Duct) Figure 16-12 shows axial sections of the pancreas head, which are situated between the homogeneous midgray liver anteriorly and the longitudinal section of the anechoic inferior vena cava posteriorly. Sagittal scanning plane images of the pancreas show the gland in axial sections. Once again, the epigastric vessels (gastroduodenal artery, common bile duct, inferior xvena cava, superior mesenteric vein, portal splenic confluence, portal vein, splenic vein, superior mesenteric artery, Chapter 16 259 The Pancreas Anterior Liver Neck Body Duodenum Gastroduodenal artery Air in duodenum Right Stomach Left Head Common bile duct Tail Portal splenic confluence Splenic vein Superior mesenteric artery Inferior vena cava Left renal vein Aorta C Right kidney Right renal artery Posterior FIGURE 16-9, cont’d C, The splenic vein runs along the posterior surface of the body. Anterior Neck Portal/splenic confluence Liver Head Body Superior mesenteric artery Splenic vein Left Tail Right Left kidney Inferior vena cava Right kidney Posterior FIGURE 16-10 Longitudinal Pancreas Body and Tail. In this transverse scanning plane image of the mid epigastrium, it is easy to appreciate the anechoic longitudinal section of the splenic vein following along the curvilinear shape of the posterior surface of the pancreas body and tail. Notice how the splenic vein enlarges at the confluence, marking the entrance of the superior mesenteric vein. (Image courtesy Jeanes Hospital, Philadelphia, Pennsylvania.) Neck (Superior Mesenteric Vein, Portal Vein, Inferior Vena Cava) As previously noted, just medial to the pancreas head, the neck and uncinate process are separated by the superior mesenteric vein. Figure 16-13 demonstrates what this anatomic relationship looks like in a sagittal scanning plane. Moving slightly more medial may move away from the uncinate process, depending on its size, which is variable. However, another section of the pancreas neck and superior mesenteric vein should be viewable (Figure 16-14). Body and Tail (Splenic Vein, Superior Mesenteric Artery, Aorta) Slightly medial to the pancreas neck, the body of the pancreas is situated between the splenic vein (posteriorly) and the stomach and liver (anteriorly). The normal pancreas body is anterior to, and in the same plane as, Portion of duodenum partially filled with fluid Anterior Body Anterior abdominal wall (muscle and tissue) Neck Right Fluid-filled stomach Left Liver Splenic vein Head Tail Superior mesenteric Portal splenic artery confluence Aorta Posterior Inferior vena cava FIGURE 16-11 Longitudinal Pancreas Body and Tail. Mid-epigastric transverse scanning plane image showing a longitudinal section of the pancreas body and tail. Observe how the splenic vein hugs their posterior surface along its course to the confluence, making it an excellent vascular landmark. Anterior Liver Hepatic artery Head Superior Inferior Portal vein Inferior vena cava Right renal artery A Posterior Anterior Duodenum Stomach Liver Hepatic artery Pancreas head Portal vein Superior Inferior Common bile duct B Inferior vena cava Right renal artery Posterior FIGURE 16-12 Axial Pancreas Head. A, B, and C are sagittal scanning plane images just to the right of the midline, highlighting axial sections of the pancreas head. A demonstrates an axial section of the pancreas head sandwiched between the liver (anteriorly) and inferior vena cava (posteriorly). Observe the anechoic, axial sections of the portal vein and hepatic artery just superior to the head. Notice how the small, anechoic, axial section of the right renal artery is posterior to the inferior vena cava and head of the pancreas. In B, the head of the pancreas is clearly demonstrated just anterior to the anechoic, longitudinal section of the inferior vena cava and posterior to the liver. The small, anechoic, longitudinal structure in the posterior portion of the head is the common bile duct. Observe a portion of the duodenum, axial sections of the portal vein and hepatic artery superior to the head. (A, Image courtesy Jeanes Hospital, Philadelphia, Pennsylvania.) Chapter 16 261 The Pancreas Anterior Hepatic vein branch Superior Liver Inferior Portal vein Stomach Wirsung’s duct Head C Duodenum Common bile duct Posterior Inferior vena cava FIGURE 16-12, cont’d In C, the axial section of the head is seen immediately anterior to the long, anechoic section of the inferior vena cava. Observe the long, anechoic section of Wirsung’s duct (main pancreatic duct) in the central portion of the head and the long, anechoic section of the common bile duct posteriorly. Also note the food and fluid in the stomach and duodenum anterior and superior to the head of the pancreas. Anterior Portal vein Superior Inferior Liver Neck Superior mesenteric vein Uncinate process Inferior vena cava Posterior FIGURE 16-13 Axial Pancreas Neck. Sagittal scanning plane image just medial to the level of the head of the pancreas. Note the axial sections of the pancreas neck (anteriorly) and uncinate process (posteriorly) separated by the anechoic, longitudinal section of the superior mesenteric vein. Note how the uncinate process sits directly anterior to, or in front of, the longitudinal, anechoic section of the inferior vena cava. The level where the pancreas neck is anterior to the superior mesenteric vein and uncinate process is a level slightly inferior to the level of the portal splenic confluence. 262 Section III ABDOMINAL SONOGRAPHY Anterior Pancreas neck Liver Superior Inferior Superior mesenteric vein Portal vein Crus of the diaphragm Inferior vena cava Posterior FIGURE 16-14 Axial Pancreas Neck. Sagittal scanning plane image of the abdomen at the level of the neck of the pancreas. Note the axial section of the midgray neck located immediately anterior to the anechoic long section of the superior mesenteric vein. (Image courtesy Jeanes Hospital, Philadelphia, Pennsylvania.) Anterior Body Liver Stomach Superior Inferior Splenic vein Superior mesenteric artery Splenic artery Aorta Posterior FIGURE 16-15 Axial Pancreas Body. Sagittal scanning plane image of the abdomen just to the left of the midline, showing an axial section of the body of the pancreas inferior to the anechoic, long section of the celiac axis/splenic artery, immediately anterior to the anechoic axial section of the splenic vein, anterior to the anechoic long sections of the superior mesenteric artery and aorta, and posterior to portions of the liver and fluid-filled stomach. the superior mesenteric artery and abdominal aorta (Figures 16-15 and 16-16). The body of the pancreas merges left laterally into the tail. Again, the best vascular landmark to help identify the tail is the anechoic splenic vein running along its posterosuperior surface. The tail can also be identified anterior to the left kidney (Figures 16-17 and 16-18). SONOGRAPHIC APPLICATIONS Uses of pancreatic sonography include the following: • Structural measurements • Associate distal biliary tree measurements • • • • • • Identification of pancreatic masses Identification of epigastric masses Main pancreatic duct measurements Adjacent associated biliary masses Associated biliary obstruction Diagnosis and follow-up evaluation of acute and chronic pancreatitis • Diagnosis and follow-up evaluation of pancreatic pseudocysts • Endoscopic pancreatic ultrasound for identification of pancreatic lesions on patients whose CT results were inconclusive Chapter 16 The Pancreas 263 Anterior Splenic vein Splenic artery Superior Body Liver Inferior Diaphragm Esophageal gastric junction Superior mesenteric artery Aorta Spine Posterior FIGURE 16-16 Axial Pancreas Body. Sagittal scanning plane image of the abdomen just to the left of the midline, showing another axial section of the body of the pancreas inferior to the anechoic long section of the celiac axis/splenic artery, immediately anterior to the anechoic axial section of the splenic vein, anterior to the anechoic long sections of the superior mesenteric artery and aorta and posterior to a portion of the liver. Anterior Left lobe of liver Bowel Tail Superior Inferior Splenic vein Left kidney Posterior FIGURE 16-17 Axial Pancreas Tail. Sagittal scanning plane image of the abdomen slightly left lateral to the aorta. An axial section of the tail of the pancreas is noted between the liver (anteriorly) and left kidney (posteriorly). Note the portion of bowel anteroinferiorly to the tail and the axial section of the anechoic splenic vein along the tail’s posterior margin. (Image courtesy Jeanes Hospital, Philadelphia, Pennsylvania.) NORMAL VARIANTS • Annular pancreas: A condition in which a ring of pancreatic tissue surrounds the second portion (C-loop) of the duodenum. • Ectopic (heterotopic, aberrant) pancreas: Tissue that has no vascular or structural connection to the body of the pancreas. Because ectopic tissues may be as small as 1 cm in size, the condition can be difficult to detect with sonography. • Partial duplication of the pancreas tail: Rare variation. Sonographically, the tail may appear to be grossly enlarged (see Figure 16-18). 264 Section III ABDOMINAL SONOGRAPHY Anterior Superior Inferior Liver Tail Splenic vein Left kidney Posterior A Neck Head Anterior Duodenum Gallbladder Splenic vein Liver Inferior vena cava Body Superior mesenteric artery Right Left Tail Aorta Right kidney B Right renal artery Left renal artery Posterior Left kidney FIGURE 16-18 Pancreas Tail. A, Sagittal scanning plane image of the abdomen, just to the left of the midline, showing an axial section of the pancreas tail situated between a long section of the left lobe of the liver (anterosuperiorly) and long section of the left kidney (posteriorly). Note the anechoic axial section of splenic vein between the tail and left kidney. B, Transverse scanning plane image of the mid epigastrium, demonstrating an enlarged tail of the pancreas. This patient has a congenital malformation in which the tail is partially duplicated. REFERENCE CHARTS ASSOCIATED PHYSICIANS • Internist: Involved in diagnosing and treating pancreatic disease. • Radiologist: Interprets/diagnoses imaging modality tests used to evaluate the pancreas and related diseases. • Surgeon: Involved in surgery of the pancreas. COMMON DIAGNOSTIC TESTS • General radiography: Except for the appearance of calcifications, plain radiography is not very revealing for pancreatic disease. An upper gastrointestinal (UGI) series, a study in which the patient swallows barium to outline the stomach and duodenum, detects pancreatic masses or enlargement through displacement of the C-loop of the duodenum by the mass. The UGI series is performed by a radiologist assisted by a radiologic technologist. The radiologist interprets the findings. Chapter 16 • Endoscopic retrograde cholangiopancreatico­ duodenography (ERCP): A tube is placed into the duodenum via the esophagus and stomach. Within the tube are fiberoptics to allow visualization of the anatomy and a means for inserting a catheter. The catheter tip is placed in the end of the common bile duct (or the pancreatic duct, depending on the anatomic configuration). A contrast medium is injected into the biliary system, which visualizes structures in retrograde order (in the reverse direction). This examination is usually performed and interpreted by a radiologist and/or gastroenterologist assisted by a radiologic technologist. • Computed axial tomography (CT) scan: An x-ray beam passes through the patient to be detected by a series of devices that provide an electrical signal to a computer. The computer then arranges the data into a sectional image of the body. Structural and some functional information is obtained. A contrast material may or may not be administered. This examination is performed by a radiologic technologist, and the findings are interpreted by a radiologist. • Magnetic resonance imaging (MRI): Images are similar in format to those of a CT scan; however, the images are generated using a strong magnetic field instead of radiation. An MRI technologist or a radiologic technologist performs the examination, and a radiologist interprets the findings. • Angiography: A contrast material is injected into an epigastric vessel to visualize the vascularity of the pancreas of a suspected lesion. This examination is performed by a radiologist assisted by a radiologic technologist. The radiologist interprets the findings. The Pancreas 265 LABORATORY VALUES SERUM TESTS Amylase Lipase Glucose (fasting) (all sugars) URINE TESTS Amylase (2 hr) Alkaline phosphatase 60–80 units 1.5 U/mL 65–110 mg/dL 80–20 mg/dL 35–260 units/hr <3.5 U/8 hr VASCULATURE Arterial supply to the head and neck of the pancreas: Gastroduodenal artery → pancreaticoduodenal arteries → pancreatic arcades Arterial supply to the body and tail of the pancreas: Pancreatic splenic artery → suprapancreatic splenic artery → pancreatic splenic artery → prepancreatic splenic artery → prehilar splenic artery AFFECTING CHEMICALS Prolonged alcohol ingestion over a period of years (alcoholism) is toxic to the pancreas.