PANCREAS ULTRASOUND TECHNIQUES

PANCREAS - Ultrasound techniques
Because the pancreas lies posterior to the stomach and duodenum, a variety of techniques must usually be employed to examine it fully. Although ultrasound may still be considered the first line of investigation, CT, MRI and/or endoscopic retrograde cholangiopancreatography (ERCP) are frequently required to augment and refine the diagnosis. The operator must make the best use of available acoustic windows and different patient positions and techniques to investigate the pancreas fully. The most useful technique is to start by scanning the epigastrium in transverse plane, using the left lobe of the liver as an acoustic window. Using the splenic vein as an anatomical marker, the body of the pancreas can be identified anterior to this. The tail of pancreas is slightly cephalic to the head, so the transducer should be obliqued accordingly to display the whole organ.

Different transducer angulations display different sections of the pancreas to best effect:
● Identify the echo-free splenic vein and the superior mesenteric artery posterior to it. The latter is surrounded by an easily visible, hyperechoic fibrous sheath. The pancreas is ‘draped’ over the splenic vein.

● Where possible, use the left lobe of the liver as an acoustic window to the pancreas, angling slightly caudally.

● The tail, which is often quite bulky, may require the transducer to be angled towards the patient’s left. The spleen also makes a good window to the tail in coronal section.

If you can’t see the pancreatic head properly, turn the patient left side raised, which moves the duodenal gas up towards the tail of the pancreas. Right side raised may demonstrate the tail better. If these manoeuvres still fail to demonstrate the organ fully, try:
—asking the patient to perform the Valsalva manoeuvre with abdominal protrusion
—scanning the patient erect
—filling the stomach with a water load to create an acoustic window through which the pancreas can be seen.

Ultrasound appearances
The texture of the pancreas is rather coarser than that of the liver. The echogenicity of the normal pancreas alters according to age. In a child or young person it may be quite bulky and relatively hypoechoic when compared to the liver. In adulthood, the pancreas is hyperechoic compared to normal liver, becoming increasingly so in the elderly, and tending to atrophy. The pancreas does not have a capsule and its margins can appear rather ill-defined, becoming infiltrated with fat in later life. These age-related changes are highly significant to the sonographer; what may be considered normal in an elderly person would be abnormally hyperechoic in a younger one, and may represent a chronic inflammatory state. Conversely a hypoechoic pancreas in an older patient may represent acute inflammation, whereas the appearances would be normal in a young person. The main pancreatic duct can usually be visualized in the body of pancreas, where its walls are perpendicular to the beam. The normal diameter is 2 mm or less. The common bile duct can be seen in the lateral portion of the head and the gastroduodenal artery lies anterolaterally. The size of the uncinate process varies.

Pitfalls in scanning the pancreas
The normal stomach or duodenum can mimic pancreatic pathology if the patient is insufficiently fasted. A fluid-filled stomach can be particularly difficult when looking for pancreatic pseudocysts in patients with acute pancreatitis. Giving the patient a drink of water usually differentiates the gastrointestinal tract from a collection. Epigastric or portal lymphadenopathy may also mimic a pancreatic mass. If careful scanning and appropriate patient positioning are unable to elucidate, CT is normally the next step.

Biochemical analysis
In many pancreatic diseases, the production of the digestive pancreatic enzymes is compromised, either by obstruction of the duct draining the pancreas or by destruction of the pancreatic cells which produce the enzymes. This can result in malabsorption of food and/or diarrhoea. The pancreas produces digestive enzymes, amylase, lipase and peptidase, which occur in trace amounts in the blood. If the pancreas is damaged or inflamed, the resulting release of enzymes into the blood stream causes an increase in the serum amylase and lipase levels. The enzymes also pass from the blood stream into the urine and therefore urinalysis can also contribute to the diagnosis.