Ultrasound of the Pancreas - SD

Introduction

Hello everyone.

My name is Anne Kennedy. I'm a radiologist working at the University of Utah in Salt Lake City in the USA. I actually do women's imaging as a career, but I am part of the abdominal imaging section and one of my colleagues asked me to put together a talk on pancreas ultrasound for a session on abdominal imaging at the SRU meeting in Chicago this November, 2011.

I did that and I will admit that I am not a great advocate of pancreatic imaging, but I think everything with ultrasound, if you apply yourself, there are many things that you can see and do to assist and triage of patients.

We're gonna talk about ultrasound of the pancreas.

Approaches to Imaging the Pancreas

If you think about imaging the pancreas, in many cases, ultrasound doesn't come to your mind as the first modality. Most people think about C-T-N-M-R-I first, but many, many patients come into the healthcare system via the ultrasound department, either from the emergency room or for their family practice doc with things like vague abdominal pain, maybe abnormal liver function tests.

When you think about ultrasound, there's a couple of different ways of approaching the pancreas. The standard one that we as radiologists use is the transabdominal approach, but our GI partners use endoscopic ultrasound. Our surgical colleagues use intraoperative ultrasound and our more imaginative colleagues are actually figuring out ways where you can use fiber optic technology to use intraductal ultrasound whereby you're actually scanning the pancreas from inside the main pancreatic duct.

There are also techniques like elastography and contrast enhanced ultrasound that are not necessarily widely available but have potential to help us with differential diagnosis.

And these are just some pictures that I have downloaded from the internet. This is elastography and it shows the difference between a malignant and a benign lesion. Malignant needles are very densely fibrotic and tend to be hard, and so they come out looking blue on the elastography. More benign masses, such as focal inflammation, tend to be less fibrous, less SRUs, and come out in the shades of yellow and green.

Similarly, contrast enhancement of ultrasound is widely available in Europe and Asia. It is not FDA improved in the UH, USA unfortunately, but this is an example showing a swollen emus pancreatic body and tail following contrast administration. The body enhances here, but the tip of the tail does not. And this indicates pancreatic necrosis, which is a very important complication of acute pancreatitis.

And the beauty of this is that this exam can be performed at the patient's bedside in ICU. No need to transfer very sick ventilated patients down to to the CT scanner.

Image-Guided Biopsies

The other thing that we often do in the ultrasound department is do image guided biopsies and you can certainly use ct, but ultrasound allows you real time visualization to look at your needle position at all times. We can do transabdominal, um, ultrasound guided biopsy. Similarly, our GI colleagues can do endoscopic biopsy and this is an example of this with a lesion coming through the stomach wall into a pancreatic mass and the needle clearly in the lesion there.

Our surgical partners use intraoperative ultrasound to localize masses. This is actually in the liver, but they can do the same in the pancreas, either to perform a biopsy for frozen section or to help them create their surgical planes for excision of a mass as a prenatal imager.

Embryology and Anatomy

Everything that I do revolves around embryology and anatomy and the pancreas arises from two buds, a dorsal and a ventral. One arises near the stomach and the ventral arises near the liver. As the GI tube elongates and curves, these buds migrate and eventually fuse.

The dorsal bud forms the pancreatic body and tail. The ventral bud forms part of the inferior portion of the head and the annu process, the normal arrangement is that the duct from the main body entail unites with the duct from the ventral component to form the main pancreatic duct and the distal portion of the dorsal duct atrophies or becomes the accessory duct of Santorini.

If that doesn't happen, you have um, pancreas divis where the ventral portion drains into the major papilla, which is where the most of the ducts should go, and the main portion of the pancreas actually drains to the minor papilla. This is not something that's easily seen on ultrasound, but it is an important developmental variant because it can predispose to acute pancreatitis.

Other Developmental Variants

Other developmental variants to think about are migrational abnormalities and you can have ectopic pancreas left where these little buds migrate down to their final location. Those are most common in the gastric mucosa or in meles diverticulum.

The annular pancreas occurs when the buds, instead of getting to one side of the duodenum, infusing actually encircle the duodenum and obstructed and this is a radiograph of a fetus. Well, it was a fetus that I saw. This is the radiograph of the newborn infant and you can see the double bubble sign with a dilated stomach dilated duodenum.

And we thought prenatally that this was not typical for a duodenal atresia as might be seen in down syndrome because the degree of obstruction seemed to be too far into the second portion of the duodenum. And we actually raised the possibility of annular pancreas as part of the diagnosis and the baby was delivered in, had an a gastric tube placed correctly and was taken to the local pediatric hospital, which is across a walkway from our institution and had surgery confirming an annular pancreas.

There are many contour abnormalities that happen if the buds fuse in an unusual manner, and this is just an example from the literature showing the bifid pancreatic tail, um, that you may see if the buds don't unite in the conventional manner.

Normal Anatomy

Anatomy is everything in terms of imaging diagnosis. If you don't understand your normal anatomy, you can't pick out pathology. So the pancreas is a retroperitoneal organ. It lives in the anterior pararenal space. It's deep to the stomach, the colon, the greater momentum and the left lobe of the liver.

The spinal vein is a structure that marks the dorsal or posterior border of the body and tail. The neck is marked by the confluence of the SMV and uh, spinal vein to form the portal vein. The only parts of the pancreas that are actually behind vessels are the head and internet process, which wrap around the venous confluence so that you actually have pancreatic tissue posterior to the SMV and SMA.

The head itself is nestled into the curve of the duodenal loop and the spanic tail or the the tail of the pancreas goes up to the Hispanic hilum. And of course, although it's not in this image, the Hispanic flexor of the colon sits up here as well.

The celiac axis marks the upper border of the pancreas and the SMA travels behind the body of the pancreas in between the body and the s the internet process.

Here's an example of a CT scan with contrast. This is cropped down to show pancreatic anatomy and I've put it side by side where the transverse ultrasound obtained in the epigastrium and you can see that all of the anatomy that's displayed on the CT scan is also displayed on the ultrasound.

This is the spine as shown here. This is the right kidney. Here's the right kidney on ultrasound, inferior vena cava and aorta IVC and aorta on ct. Here is the pancreas running just superficial to or anterior to the splenic vein, splenic vein, thic vein, body and tail of pancreas. And here's the portal vein confluence with the pancreatic head, the edge of which is slightly obscured by bowel gas in the duodenum and this is the bowel gas and the duodenum on ct.

If you think about the anatomy of the pancreas, the gland should be homogeneous in echogenicity and should resemble something like fine sandpaper. Overall, generally the echogenicity increases with age and part of this is due to fat deposition or fibrosis and it's usually more echogenic than the adjacent liver, but might be iso coic to it.

Depending on what textbooks you read, the size of the pancreas is highly variable. In general, the head is slightly thicker than the body which is slightly thicker than the tail and equally the duct should be at maximum size in the head, slightly less in the body and either invisible or very small in the tail.

If all pancreas is read the textbooks, they would all be shaped like a tadpole like this pancreas, but they don't all and they can come in dumbbell configurations or just unusual lumpy bumpy configurations.

Equally, if you look inital section, you can use the left lobe of the liver as an acoustic window and here you see the aorta, the SMA and the SMV. This is part of the pancreatic head scene and sagittal section and some of the tissue wraps around in between the S-M-A-S-M-V and the aorta.

Technique for Transabdominal Ultrasound

To give you an epigenic focus here, your technique trans abdominally, it is vital that the patient be fasted. Everyone knows in the ultrasound world that bowel gas is the enemy, so you like to have your patients fasted, preferably overnight.

You can use a variety of different transducers and a variety of different scan planes and if you are unsuccessful with the patient just fasted, you can try a water bolus in the stomach as an acoustic window and in countries where uh, ultrasound contrast is available, you can give that and that may be vitally important in differentiating between a hypovascular carcinoma and a hypervascular inflammatory mass.

Pancreatic Transplants

Also, surgeons do pancreatic transplants nowadays in the diabetic population. If you're going to evaluate a pancreatic transplant on ultrasound, it is vital that you know the surgical anatomy. You need to know where the surgeon placed the organ and what kind of anastomosis they made.

There are two types. There is one that's called the systemic bladder type in which the pancreatic venous drainage, which is via the splenic vein, is connected to this donor's iliac vein and the exocrine function is directly attached to the bladder. This is technically easier for the surgeon but is not physiologically very correct.

The technically harder process is whereby the splenic vein drain from the transplant is connected to the recipient SMV, so it goes into the portal system as it does in the normal arrangement. And the pancreatic head exocrine function is connected to the recipient's GI tract so that again, the um, exocrine secretions go into the normal route rather than going into the bladder and being reabsorbed.

Transducer Selection

Transducer selection, the curved six megahertz transducer is your workhorse and abdominal imaging and as you can see in this picture, you can actually lay out the entire length of the pancreas with good transducer pressure. This is the spine, the aorta, this is the splenic vein coming along here. This is part of the SMA and the SMV is actually obliterated by transducer pressure here. This is part of the splenic flexor of the colon, but it's being compressed so the air is not shadowing out the pancreatic tail.

If you have a very slim patient, you can even bring out the linear transducers and here you can see with a nine megahertz, a ear transducer that you appreciate the marbleization of the normal pancreatic contour.

Scan Planes

What scan planes do we use? We start transverse in the epigastrium and in that view you should see the neck, the body and part of the head. Remember that the medial portion of the head is going to be partly obscured by gas in the geo deum.

If you turn sagittal in the epigastrium, you can see the head and you can see the anther process tuck in behind the SMA and the SMV. An oblique left subcostal view will allow you to follow the tail out to the splenic hilum and an oblique right up Subcostal view is essential to look at the gallbladder and biliary tree because many processes that affect the gallbladder um, also affect the pancreas such as stones. And if you have a pancreatic mass, you may inhibit biliary drainage.

If you um, have limited views with the patient sitting or lying down fasted, you can then have the patient sit up. This shifts the diaphragm down somewhat and may reorient bowel gas and give you a better window. And you could also try the water bolus technique in which you have the patient sip about 500 mls of still water. Wait for approximately 10 minutes for any bubbles to settle and then use the water-filled stomach as an acoustic window to the pancreas.

After you have looked at the body and tail of the pancreas, you turn the patient right lateral decubitus and the water will run into the duodenal loop, which then acts as an acoustic window to the pancreatic head.

Examples of Normal Anatomy

Here's some normal anatomy transverse in the epigastrium left lobe of liver. This is the body of the pancreas. This is going down into the head. This is the pancreatic duct well seen where the beam is perpendicular. This is the pancreatic tail extending up into the left upper quadrant. Left renal vein is compressed between the aorta and the SMA as we apply transducer pressure to clear out all this anatomy. And here's the inferior vena CAA and the spine.

In the epigastrium you turn longitudinal. Here's the liver. Patient's head is now at this end of the picture. Here's the transverse colon. The SMV is nicely elongated. Here's the aorta, you see the gastroduodenal artery and the common bile duct both in the pancreatic head with that little lip of tissue from the unsnap process tucking in behind the vessels.

Similarly, here we have the SMA elongated in front of the aorta. The SMV is not so well seen in this image. This is pancreatic tissue. This is pancreatic tissue.

Oblique left subcostal as I showed you before, you can lay out the pancreatic tail very nicely and oblique right subcostal. Here is your common bile duct paralleling the portal vein gallbladder, no evidence of stones or biliary dilatation.

Endoscopic Ultrasound

Endoscopic ultrasounds in my institution performed by my GI colleagues. This is an example of the transducer within the stomach and this shows this obvious in homogenous mass, which is accessible to FNA. This is another example where you can see the dilated common bile duct and the dilated main pancreatic duct coming down to a mass in the head of the pancreas. And this again is a typical appearance for an adenocarcinoma of the pancreas causing biliary and pancreatic ductal dilatation. And you can see how easy it would be to get a needle in here for an endoscopic biopsy.

Pathology of the Pancreas

So when you think about what you can see in terms of pathology in the pancreas after anatomic variants, you essentially have pathologies that are either inflammatory or neoplastic. And of course we have to think about the pancreatic transplant population in whom we are looking for complications of transplant.

This is utilizing the extended field of view or seascape and this is a newly placed pancreatic transplant. This is the associated renal transplant over here. There is echogenic fluid around the transplant, but the patient did very well initially and I'll show you later pictures of his when we performed a biopsy to look for rejection.

Pancreatitis

The different types of pancreatitis are listed here and we'll discuss some of those in more detail and we'll also review some of the findings of the various types of neoplasia.

Acute Pancreatitis

So in acute pancreatitis, we've all seen as radiologists, the patient come in from the emergency room with right upper quadrant pain. You see some gold stones. Patient has an elevated amylase and they go on to CT and have really quite marked inflammatory changes that were not that obvious on ultrasound.

The findings can be extremely subtle and the key to make the diagnosis to actually look for ancillary signs of inflammation. So this is a patient with acute pancreatitis and the pancreatic head, although the genicity is normal, it is slightly thickened and if you look over here there's fluid around the right kidney. There's quite marked gallbladder wall thickening. There were no gallstones and no sonographic Murphy sign.

Here's a list of all the features that you can look for for signs of inflammation based on a study which was published in the ultrasound quarterly in 2005.

This is a left pleural effusion and this is a right pleural effusion and I'm going to show you more images of that same patient that I showed you earlier. Now to prove that you really can do this, here's your mildly edematous, slightly thickened pancreatic head. Here is the perico cystic edema and gallbladder wall thickening. I showed you fluid around the right kidney earlier. Here is fluid around the left kidney. And here again right pleural effusion with atelectasis in the right lower lobe left pleural effusion adjacent to the spleen.

So all of these are indications of a diffuse inflammatory process in the abdomen.

Complications of Acute Pancreatitis

Complications of acute pancreatitis include necrosis, abscess, vascular complications. Later on you may form a pseudocyst or develop chronic pancreatitis and this is an example of chronic pancreatitis. This is the spanic vein which marks the dorsal border of the pancreas. So this is the dilated pancreatic duct which contains calculi. And these are the same calculi showing twinkle artifact on color Doppler.

Pancreatic pseudos are communists in the body of the tail. And you can see this nicely demonstrated in this graphic. They may be very circumscribed and smooth walled, but they can of course be multilocular and they contain internal echoes sometimes particularly in the acute situation where they may be complicated by hemorrhage or infection.

The utility of ultrasound in this circumstance is to be able to guide a needle into that fluid collection because a pancreatic abscess is a surgical emergency, whereas isolated hemorrhage into a pseudocyst does not require a surgical procedure. And if pseudocysts become big enough, they can cause duct obstruction, which then increases the likelihood of more episodes of pancreatitis.

Chronic Pancreatitis

Chronic pancreatitis eventually causes atrophy of the gland. The ducts will dilate and that is a very common finding. And in fact, if you see calcifications within a dilator duct, it is virtually diagnostic of chronic pancreatitis.

One thing to remember is that chronic pancreatitis does not have to involve the whole gland. It can actually be focal. And if so, it can be very difficult to differentiate focal pancreatitis from a focal mass such as uh, pancreatic cancer. Elastography and contrast enhancement may help us with that. But oftentimes it comes down to needing a biopsy groove.

Groove Pancreatitis

Pancreatitis is a variant of pancreatitis that is relatively recently described and it focally involves part of the pancreatic head tucked into the curve of the duodenal loop and is associated with cystic abnormalities in the duodenal wall. And this was a patient that came from the emergency room with right upper quadrant pain. Look for gallstones. One of my previous fellows noticed the I irregularity of the pancreatic head and suggested groove pancreatitis, which was confirmed on this ct.

And this is an important diagnosis to be aware of because these are frequently misdiagnosed as pancreatic carcinomas. And given the location on the pancreatic head, these patients may be set up for uh, whipples surgery and that is a huge operation that is not necessary for a benign process. So be aware of groove pancreatitis.

Autoimmune Pancreatitis

There's another condition called autoimmune pancreatitis, which is also relatively new in terms of ultrasound features. And what you see with autoimmune pancreatitis is diffuse thickening of the pancreas with ill-defined anterior margins. And you cannot identify the pancreatic duct anywhere within this mass of pancreatic tissue.

It's a systemic disease caused by deposition of IgG four antibodies and is associated with biliary changes. So very often you'll see biliary dilatation in association with this thick in homogeneous pancreas. In fact, if you look at the biliary system carefully in patients, there's a characteristic appearance called the trilaminar appearance and you'll see this striped appearance to the dilated common bile duct wall or to the gallbladder wall.

And if you see this in association with the thick, ugly edematous looking pancreas like this, you can suggest the diagnosis of autoimmune pancreatitis, which can be verified with a simple blood test.

Pancreatic Masses and Neoplasms

Pancreatic masses primarily you're worried about uh, pancreatic neoplasms. There are many mimics though, and this is where it becomes complicated because just the developmental abnormalities we spoke about where the buds don't fuse in the conventional manner. If there's a pseudocyst that's complicated. If there's something in the duodenum, if there's a lipoma, if there's either focal fatty replacement of the pancreas or focal fatty sparing, you can appear to have a mass and focal inflammation. Focal pancreatitis as opposed to diffuse different type of neoplasms are mentioned here. And introductory papillary mucinous neoplasia is also an issue because you may just see a dilated pancreatic duct on ultrasound and these are low grade malignancies with the potential to develop an adenocarcinoma over time.

Pancreatic Cancer

Pancreatic cancer is um, an unfortunate cancer. It tends to be quite advanced at the time of diagnosis so that 90% of patients are unresectable. The long-term survival is very poor and many patients already have vascular encasement and lymphadenopathy and metastases at the time they present.

Here's an example, lady came in, she had been traveling on a cruise ship earlier in the year and had developed diarrhea as had many of the passengers, but her diarrhea did not settle and she had precipitous weight loss. As part of her workup in the infectious diseases lab, she had liver function tests obtained which were abnormal and she was sent for an ultrasound to evaluate, uh, primarily the gallbladder and liver.

What we saw was this irregular in homogeneous mass with chunks of calcification that was occupying most of the pancreatic head abutting the portal vein and here's part of the pancreatic tail with what appears to be a normal duct, but over here you have this hypoechoic area that is different to the texture of the rest of the pancreas. We were very concerned for the possibility of a pancreatic carcinoma Here we looked around. This again is the mass in the pancreatic head. The common bile duct was not dilated because remember this lady presented with abnormal liver function tests. She had some cystic masses in the abdomen, but she also had masses that had um, papillary expressives. One of these was biopsied and it confirmed pancreatic adenocarcinoma as a primary.

Here's the CT scan that shows this mass in the pancreatic head actually encircling the portal vein confluence. And here along the pancreatic tail you see the reason for that hypoechoic area. This in fact was an IPMN with subsequent development of an adenocarcinoma in the head. And here are correlative images from the MR and the um, pet CT

Cystadenomas

cy adenomas are benign. They often present as a highly echogenic mass because there are multiple tiny cystic spaces which create multiple interfaces and look rather like the appearance we see in autosomal recessive polycystic kidneys In the fetus where you don't resolve the cyst, you simply see the echogenicity from the interfaces.

Um, mucin cyst adenoma on the other hand has larger spaces and inter interstices. And here is an example of this where you have this fairly benign looking cystic uh, lesion in the pancreatic tail. This is the ple vein marking the dorsum of the pancreas. So this is pancreatic body and tail and you note the small papillary expressions in this mass, which turned out to be a mucinous cystadenoma. Although these are malignant, they're generally low grade and they don't have as bad a prognosis as the conventional ductal adenocarcinoma.

Islet Cell Tumors

Eyelet cell tumors are either functional or non-functional. The functional ones like in melanoma present early because of their hormonal production, but they are small and hypervascular and can be very hard to see. Obviously endoscopic ultrasound and contrast enhanced ultrasound will be beneficial in looking for small lesions like this.

The larger tumors are often necrotic with metastasis by the time they present and they are easier to find other masses that affect the pancreas.

Metastatic Disease and Other Mimics

Metastatic disease is always a consideration and I had never seen a pancreatic metastasis until just recently. And of all things this mass in the tail of the pancreas here is a metastatic, uh, deposit from a carcinoid tumor of the cervix and a 26-year-old woman. So nothing is impossible.

Lymphoma is the great pretender. Lymphoma can do anything anywhere. It can cause diffuse per pancreatic infiltration or so can acute pancreatitis. But you look for lymph nodes in the re region. You look for systemic symptoms and you check the uh, laboratory findings.

Focal or groove pancreatitis, remember we mentioned is always localized in the pancreatic head adjacent to the duodenum, not to be mistaken for an adenocarcinoma so that you can protect a patient from having an unnecessary pancreatic resection.

This is an example of focal fatty sparing. This is a diffusely fat replaced pancreas. And so the area that was relatively normal in genicity stood out from the background and looked like a mass in the converse to this, you can get focal fat deposition in an otherwise normal genicity pancreas. And many of these things will need a biopsy to definitively exclude malignancy.

Pitfalls in Pancreatic Ultrasound

It falls in pancreatic ultrasound, include, um, body habitus, bowel gas, and the examiner's unwillingness to try with endoscopic ultrasound. It's hard to be clear reading the literature because different descriptors are used and there's a big move to standardized omere in the literature so that uh, different users can get together and pull their data.

And even with intraoperative ultrasound, the surgeons may experience trouble by using too much manual pressure occluding vessels and by having the afield reverberation, this is an example where we thought, oh, there's a mass in the pancreatic body and tail here. Look at this hypo coic thing. It persists, it's hypovascular. This must be a pancreatic cancer. Doesn't look like it's invading any vessels. This is potentially a great save. But when the lady went on to ct, this is a completely normal pancreas and this is an example of the dumbbell configuration of the pancreas with a much thicker pancreatic tail than one normally expects to see.

Pancreatic Transplant Evaluation

For the last few minutes of the talk, we're going to talk briefly about uh, pancreatic transplant evaluation. This is just to remind you of the two different surgical techniques and that you need to meet with your surgeon prior to performing the ultrasound so you know where the pancreas is in the patient's abdomen. You're looking for things like rejection, fluid collections, focal pancreatitis, leaks of fluid and vascular problems.

Here is an immediate postoperative study. There's some free fluid in the abdomen, which is not unusual post-op. Here are the iliac vessels and you know that the vessels are going to be anastomosis to the iliac vessel in this type of pancreatic transplant. And here these parallel lines are actually the pancreatic duct in the transplanted pancreas.

Here's another example where this is the pancreatic transplant. And even with the use of power doppler, we were unable to demonstrate much in the way of any flow and spectral doppler was very abnormal and this was a pancreatic transplant with um, vascular thrombosis of the veins.

Here's another pancreatic transplant, very conventional looking pancreatic head in the right lower quadrant. Single vessel seen nicely on color doppler. Spectral doppler shows very, very abnormal waveform with reversed end diastolic flow. And again, this was a venous thrombosis of a pancreatic transplant.

Lastly, this is the chap that I showed you up back at the beginning. It had a pancreatic transplant surrounded by lots of echogenic fluid. He did well, went home and he was back for a biopsy to look for rejection. This is the pancreatic head right beside the transplant kidney in the right lower quadrant. And as you can see there are many small arterial branches all around this pancreatic head. That's the portal vein of the donor into the recipient's iliac vein. So a highly vascular structure.

With ultrasound, we were able to line up with the short throw of the biopsy needle look with color doppler prior to taking this specimen and see that each, um, biopsy went through an area of the pancreas that would avoid those big surrounding vessels.

Conclusion

So in conclusion, I want to say when you think about pancreas ultrasound, don't go, oh no. It is a retroperitoneal organ. It is often hidden behind fat and bowel, but with appropriate transducer selection and appropriate technique, you can see a lot of pathology and make a lot of diagnoses.

Thank you.