Diagnostic Ultrasound - Abdomen and Pelvis

Pancreas
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Anatomy: Abdomen
GROSS ANATOMY
Overview
• Pancreas: Accessory digestive gland lying in
retroperitoneum behind stomach
○ Exocrine function: Pancreatic acinar cells secrete
pancreatic juice → pancreatic duct → duodenum
○ Endocrine: Pancreatic islet cells (of Langerhans) secrete
insulin, glucagon, and other polypeptides → portal
venous system
Divisions
• Head: Thickest part; lies to right of superior mesenteric
artery and vein (SMA, SMV)
○ Attached to "C" loop of duodenum (2nd & 3rd parts)
○ Uncinate process: Head extension, posterior to SMV
○ Bile duct lies along posterior surface of head, joins with
pancreatic duct (of Wirsung) to form hepatopancreatic
ampulla (of Vater)
○ Main pancreatic and bile ducts empty into major papilla
in 2nd portion of duodenum
• Neck: Thinnest part; lies anterior to SMA, SMV
○ SMV joins splenic vein behind pancreatic neck to form
portal vein
• Body: Main part; lies to left of SMA, SMV
○ Splenic vein lies in groove on posterior surface of body
○ Anterior surface is covered with peritoneum forming
back surface of omental bursa (lesser sac)
• Tail: Lies between layers of splenorenal ligament in splenic
hilum
Internal Structures
• Pancreatic duct (of Wirsung) runs length of pancreas,
turning inferiorly through head to join bile duct
• Accessory pancreatic duct (of Santorini) opens into
duodenum at minor duodenal papilla
○ Usually communicates with main pancreatic duct
○ Variations are common, including a dominant accessory
duct draining most pancreatic juice
• Vessels, nerves, and lymphatics
○ Arteries to head mainly from gastroduodenal artery
– Pancreaticoduodenal arcade of vessels around head
also supplied by SMA branches
○ Arteries to body & tail from splenic artery
○ Veins are tributaries of SMV and splenic vein → portal
vein
○ Autonomic nerves from celiac and superior mesenteric
plexus
– Parasympathetic stimulation of pancreatic secretion,
but pancreatic juice secretion is mostly under
hormonal control (secretin, from duodenum)
○ Lymphatics follow blood vessels
– Collect in splenic, celiac, superior mesenteric and
hepatic nodes
IMAGING ANATOMY
Overview
• Pancreas can be localized on ultrasound by
○ Typical parenchymal architecture: Homogeneously
isoechoic/hyperechoic echo pattern when compared
with overlying liver
○ Surrounding anatomical landmarks: Body anterior to
splenic vein; neck anterior to SMA/SMV
• Variations in reflectivity related to degree of fatty
infiltration; uncinate process and posterior pancreatic head
are relatively echo-poor in 25% of subjects (lack of
intraparenchymal fat)
ANATOMY IMAGING ISSUES
Imaging Recommendations
• Use 2-5 MHz transducers, or up to 9 MHz for smaller
patients
• Techniques to combat overlying stomach and bowel gas
include
○ Displacement of intervening bowel gas by gentle firm
graded compression with transducer
○ Overnight fasting or fasting > 6-8 hours
○ Non-effervescent fluid can be given orally to fill gastric
fundus
– Scanning delayed for a few minutes to allow fluid to
settle
– Patient can lie on left side to allow imaging of body
and tail of pancreas
– Patient can then be turned right to allow gastric fluid
to flow to stomach antrum and duodenum, allowing
imaging of head and uncinate process
• CT is preferred imaging modality for imaging of pancreas
• MRCP or ERCP useful for defining pancreatic duct
Imaging Pitfalls
• Ultrasound examination of pancreas is often limited by
overlying bowel gas
Key Concepts
• Shape, size, and texture of pancreas are quite variable
○ Largest in young adults
○ Atrophy and fatty infiltration with age (> 70), obesity,
diabetes, corticosteroids, Cushing disease
○ Pancreatic duct also becomes more prominent with age
(normal < 3 mm diameter)
○ Focal bulge or mass effect is abnormal
• Location behind lesser sac
○ Acute pancreatitis often results in lesser sac fluid (may
mimic pseudocyst)
• Pancreas lies in anterior pararenal space (APS)
○ Inflammation (from pancreatitis) easily spreads to
duodenum and descending colon; also lie in APS
○ Inflammation easily spreads into mesentery and
mesocolon; roots of these lie just ventral to pancreas
• Obstruction of pancreatic duct
○ Relatively common result of chronic pancreatitis (fibrosis
&/or stone occluding pancreatic duct), or pancreatic
ductal carcinoma
• Acute pancreatitis
○ Relatively common result of gallstone (lodged in
hepatopancreatic ampulla causing bile to reflux into
pancreas) or damage from alcohol abuse