Why is it so difficult to find the pancreas on ultrasound?
The primary reason that the pancreas is difficult to visualise in normal dogs, is due to it being isoechoic to surrounding mesenteric fat.
The left limb is difficult to visualise also because of the gas-filled stomach and tranverse colon causing acoustic shadowing.
Because the normal pancreas can be so hard to find, you need to be confident with the anatomic landmarks in order to be sure that you can identify the pancreatic region and be certain that everything is normal.
The Right Lobe
Lets start with looking for the right pancreatic lobe becuase it is the easiest to visualize in the dog.
- dorsomedial to the duodenum
- ventral to the right kidney
- lateral to the portal vein
To visualise the right limb of the pancreas, obtain a longitudinal image of the descending duodenum.
How can you identify the descending duodenum?
- It has a larger diameter & increased mucosal thickness compared to other loops of small intestine. It also follows a straight and superficial course along the right body wall and should be followed caudally until it turns medially and becomes the ascending duodenum.
- The right lobe of the pancreas lies dorsomedial to it.
To confirm that you are imaging the right limb of the pancreas, look out for the “train tracks” of the pancreaticoduodenal vein running in the centre of the organ, parallel with the duodenum.
Here is an image of the right limb of the pancreas in longiudital section:
Cross-sectional images of the duodenum are very helpful for imaging the pancreas if you are unsure in longitudinal section.
The Left Lobe
As mentioned above, visualisation of the left limb of the pancreas can be tricky due to the surrounding gas-filled stomach & transverse colon getting in the way.
The left limb lies dorsal and caudal to the stomach, extending to the left between the stomach and transverse colon.
It may also be imaged in a triangular region cranial to the left kidney, caudal to the stomach, and medial to the spleen in the left cranial abdomen. Here is what that will look like on your ultrasound scan:
As you can see, you will not necessarily definitively locate the pancreas in every dog, but if you can locate this “region of the left limb” and scan the region thoroughly, you should be able to confidently conclude whether there are abnormalities present or not.
Fortunately, the right lobe seems to be the most commonly affected portion of the pancreas in dogs with acute pancreatitis.
Inflammation, edema, necrosis, and haemorrhage associated with acute pancreatitis result in the following changes on ultrasound examination:
- Pancreas itself is enlarged, irregular and hypoechoic
- Surrounding mesenteric fat is hyperechoic (due to inflammation and saponification)
- Duodenitis: descending duodenum can appear thickened, dilated & fluid-filled (ileus), or corrugated
- Focal peritoneal effusion commonly seen
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