2. ANATOMY
The pancreas is a retroperitoneal organ that develops from a
large dorsal embryologic anlage and a smaller ventral anlage.
The dorsal pancreatic anlage communicates by means of
its central duct with the duodenum and the ventral anlage
communicates with the biliary tract. During embryologic
development these pancreatic anlagen rotate with the intestinal
structures and ultimately fuse together so that the dorsal
pancreas is located anterior and superior to the ventral
pancreas.
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6. 1. The associated pancreatic ductal structures rotate with the
parenchymal structures so that the dorsal pancreatic duct
empties into the duodenum several centimeters above the
ventral duct. The ventral duct connects to the distal
common bile duct at the ampulla.
2. In 15% to 20% of people the short ventral duct drains the
head of the pancreas through the major papilla and a long
dorsal duct that drains the remainder of the pancreas
through the minor papilla. This is referred to as pancreas
divisum.
In most people the two ducts join and the minor papilla
regresses so that the entire gland is drained by one duct
that empties into the major papilla.
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16. The pancreas is divided into a head, body, tail, and uncinate
process. The uncinate process extends inferiorly and medially
from the head and is the only part of the pancreas that is
located posterior to the superior mesenteric vein. The head
is located to the right of the mesenteric vessels, and the neck
and body are located anterior to these vessels.
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18. The tail of the pancreas is located to the left of the mesenteric vessels
and extends superiorly and posteriorly to the region of the splenic
hilum. In some references the tail of the pancreas is said to
be that part that extends to the left of the vertebral column.
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20. Because of its size, location, and echogenicity, the pancreas is
one of the more difficult abdominal organs to image
sonographically.
For this reason, adjacent vascular landmarks are useful in the
localization of the pancreas.
The head of the pancreas is located immediately anterior to the
inferior vena cava.
When patients are in the left lateral decubitus or left posterior
oblique position, the head of the pancreas may slide somewhat
to the left so that it is located over the aorta.
21. The superior mesenteric vein is immediately adjacent to the
posterior aspect of the pancreatic neck and body and to the
medial aspect of the pancreatic head.
There is no retroperitoneal fat between the superior mesenteric
vein or the portosplenic confluence and the pancreas.
There is, however, a prominent ring of retroperitoneal fat that
separates the superior mesenteric artery from the pancreas.
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23. The body of the pancreas is located anterior to the splenic vein and
the portal splenic confluence.
The tail of the pancreas is located below the splenic vein.
The trifurcation of the celiac axis is located just superior to the
pancreas, and the splenic artery generally runs near the
superior aspect of the pancreas.
The gastroduodenal artery arises from the common hepatic artery
and travels inferiorly directly over the anterior and lateral
aspects of the pancreatic head.
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29. Normal pancreatic anatomy. A, Transverse view of the pancreas
shows the aorta (A), inferior vena cava (IVC), superior mesenteric
artery (S), portal splenic confluence (asterisks), head (H) and body
(B) of the pancreas, left lobe of the liver (L), common bile duct
(arrow), and gastroduodenal artery (arrowhead).
B, Longitudinal view of the body of the pancreas shows the aorta (A),
superior mesenteric artery (S), celiac axis (C), splenic vein
(asterisk), body of the pancreas (B), left lobe of the liver (L),
stomach (St), left renal vein (LRV), and distal esophagus (E).
30. C, Coronal view of the left upper quadrant shows the spleen (Sp),
splenic vein (asterisks), and pancreatic tail (T).
D, Longitudinal view of the pancreas at the level of the superior
mesenteric vein (V) shows the body of the pancreas (B) anterior
to the vein and the uncinate process (U) posterior to the vein.
31. The pancreatic duct is seen segmentally in 85% of patients.
It is most commonly seen in the body, where its walls are
perpendicular to the sound beam (see Fig.E). The portion
of the pancreatic duct that travels through the head is more
difficult to visualize sonographically. However, it is occasionally
seen medial to the distal common bile duct and should
not be confused with the bile duct or with a low-inserting
cystic duct (see Fig.F).
32. E, Transverse view of the pancreas shows the pancreatic duct (large
arrow). Also seen is the portal splenic confluence (asterisk), IVC,
common bile duct (small arrow), and gastroduodenal artery
(arrowhead).
F, Right semicoronal view of the pancreatic head shows the distal
common bile duct (small arrows) and the pancreatic duct (large
arrow). Also seen is the gallbladder (GB), which was used as a
window to see the pancreatic head.
33. When the luminal diameter is very small, the pancreatic duct may
appear as a single bright line.
The walls of the pancreatic duct should be smooth and parallel.
3 millimeters is commonly used as the upper limit of normal for
duct diameter in the body of the pancreas. However, the duct
enlarges with age.
In some patients the hypoechoic wall of the posterior surface of
the stomach rests on the anterior surface of the pancreas and
can be confused with the pancreatic duct on transverse views.
This can be avoided by scanning in sagittal plane where the
posterior wall of the stomach can be seen in continuity with
the rest of the stomach wall.
34. Pseudoduct caused by posterior gastric wall. A, Transverse view of
the epigastrium shows what appears to be a hypoechoic tubular
structure (arrow) running in the expected location of the main
pancreatic duct. B, Longitudinal view through the same region
shows that the
structure actually represents the hypoechoic muscular layer of the
wall of the stomach (arrows). It communicates with the superior,
inferior,
and anterior aspects of the gastric wall and forms the typical bull’s-
eye appearance of an intestinal structure.
35. Pancreatic echogenicity is variable, depending on the amount of
fatty replacement. The normal pancreas is equal to, or more
echogenic than, the normal liver.
The pancreas may be hypoechoic, isoechoic, or hyperechoic
with respect to the spleen. With age, pancreatic echogenicity
increases as the result of fatty replacement.
36. Normal pancreatic head variant due to differential fat
infiltration. Transverse view shows the normal hyperechoic
appearance to the anterior head (black asterisk) and a
hypoechoic appearance to the posterior pancreatic head and
uncinate process (white asterisk). Also seen is the common
bile duct (arrow), gastroduodenal artery (arrowhead), aorta
(A), inferior vena cava (C), and superior mesenteric vein (V).
37. TECHNIQUE
The pancreas scanned with patient in a fasting state.
Body of the pancreas is well seen from an anterior subxiphoid
approach using the left lobe of the liver as an acoustic
window aided by a deep inspiration.
Visualization of body of pancreas is improved by the patient, try
to push abdomen out and make a “beer belly.”
Portions of the head of the pancreas are usually seen a right
subcostal approach. Also viewed by positioning the patient in
a left posterior oblique position.
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40. To see the pancreatic tail well, it may be necessary
to have the patient drink water and to use the resulting fluidfilled
stomach as a window. Scanning from a left lateral intercostal
approach and using the spleen as a window also helps
to image the region of the pancreatic tail.
41. Normal pancreatic anatomy.
A, Transverse view of pancreas shows aorta (A), inferior vena cava
(IVC), superior mesenteric artery (S), portal splenic confluence
(asterisks), head (H) & body (B) of pancreas, left lobe of liver (L),
common bile duct (arrow) & gastroduodenal artery (arrowhead).
B, Longitudinal view of the body of the pancreas shows aorta (A),
superior mesenteric artery (S), celiac axis (C), splenic vein
(asterisk), body of pancreas (B), left lobe of liver (L), stomach
(St), left renal vein (LRV), and distal esophagus (E).
42. C, Coronal view of the left upper quadrant shows the spleen (Sp),
splenic vein (asterisks), and pancreatic tail (T).
D, Longitudinal view of the pancreas at the level of the superior
mesenteric vein (V) shows the body of the pancreas (B) anterior
to the vein and the uncinate process (U) posterior to the vein.
43. E, Transverse view of pancreas shows the pancreatic duct (large
arrow), portal splenic confluence (asterisk), IVC, common bile
duct (small arrow), and gastroduodenal artery (arrowhead).
F, Right semicoronal view of pancreatic head show distal common
bile duct (small arrows) and the pancreatic duct (large arrow),
and gallbladder (GB) which was used as a window to see
pancreatic head.
44. PANCREATITIS
Pancreatitis is an inflammatory process in the pancreas it is
diagnosed in patients with two of the following three
signs/symptoms:
(1) acute onset of abdominal pain (epigastric pain with or without
back pain).
(2) serum amylase and lipase levels elevated to three or more times
normal.
(3) characteristic findings on ultrasound, computed tomography
(CT), or magnetic resonance imaging (MRI).
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47. Pancreatic enlargement, decreased pancreatic echogenicity,
and heterogeneous echogenicity are the sonographic hallmarks
of acute pancreatitis.
Fig.,
Transverse (A) and longitudinal (B) views show an enlarged
swollen pancreas (cursors), which is isoechoic to adjacent liver
(L), pancreatic duct (arrowheads) (is dilated), portosplenic
confluence (asterisk).
48. C, Transverse view of pancreas (P) shows a localized
peripancreatic fluid collection (F).
D, Transverse view of pancreas (P) shows a small collection of fluid
(arrows) in perivascular space anterior to splenic vein (S).
49. E, Coronal view of left upper quadrant shows retroperitoneal fluid
(arrows) in perirenal region around left kidney (LK). Ascites (A) is
also seen around the spleen (S).
F, Transverse view of right upper quadrant shows a small amount of
retroperitoneal fluid (arrows) between the duodenum (D) and
right kidney (RK). Also seen ascites (A) between gallbladder (GB)
and liver (L).
50. Pseudocysts can form virtually anywhere, but most are located
near the pancreas. They have well-defined, smooth margins.
Their internal contents are usually anechoic, but the presence
of debris can result in low-level internal echoes.
Fig.,
Transverse view of the pancreas shows a well-defined fluid
collection (cursors) anterior to the pancreatic tail typical of a
pseudocyst. Also seen are a normal pancreatic duct (arrows)
and the splenic vein (V).
