Extrahepatic biliary obstruction is a reasonably common clinical scenario in older cats. Chronic cholangiohepatitis, pancreatitis and neoplasia can all cause bile duct obstruction with jaundice and high serum bilirubin. The bile duct can undergo a chronic partial obstruction from a mass or inflammatory tissue, or an acute obstruction from a calculus.

In complete biliary obstruction, the gallbladder is enlarged. The cystic duct and common bile duct become dilated and tortuous (image 1). The normal common bile duct should measure less than 4 mm in diameter. Trace it to the duodenal papilla to check for calculi and masses (image 2). The papilla should also be less than 4 mm. The one pictured here measured 3.6 mm.

Once the complete obstruction has been present for a week, the intrahepatic bile ducts also dilate. In image 3, the intrahepatic bile duct is the anechoic structure next to the gall bladder. When color Doppler is applied, there is no flow, though it is similar in size to portal and hepatic veins. The inner surface of the wall is also slightly irregular which may represent inflammatory tissue or calculus.

Nyland TG, Gillett NA. Sonographic evaluation of experimental bile duct ligation in the dog. Veterinary Radiology 1982;23:252-260.

Edema of the gall bladder wall looks like a hypoechoic layer between two hyperechcoic surfaces. It can be confused with a small amount of peritoneal effusion so look carefully at the neck and body. In the images here, you can see the anechoic peritoneal effusion surrounding the thickened gall bladder wall.

Although gall bladder wall edema can be seen with inflammatory hepatic and biliary disease, it’s also associated with other conditions including hypoalbuminemia and sepsis. These sagittal (image 1) and transverse (image 2) images of the gall bladder show edema induced by sepsis. In my experience, the edema can resolve quickly if the systemic illness improves.

Spaulding Kathy A. Gallbladder wall thickness – Ultasound corner. Veterinary Radiology & Ultrasound 1993;34:270-272.

Renal infarcts are often incidental findings in animals with chronic renal disease. Infarcts are caused by thrombi that occlude a blood vessel in the kidney. Most of the time, they are chronic and mainly made up of fibrous tissue. The classic appearance is of a hyperechoic, wedge shaped area with the wide part of the triangle at the kidney capsule. The capsule is also usually concave at the site because of fibrosis and loss of normal renal parenchyma.

Acute renal infarcts have the same etiology, but we are seeing them within a few days after they occur. What do they look like? They are more subtly hyperechoic than the chronic infarct. In image 1, the infarct is visible as an indistinct, hyperechoic wedge in the cortex of the kidney. The medulla is out of plane so most of what is visible is cortex. The second image is a color Doppler display of the blood flow in the renal vessels. You can see the signal disruption and partial void in the hyperechoic are that represents the infarct. This dog had a systemic neoplasia with infarcts affecting the kidneys and other organs. Acute renal infarcts don’t alter the shape of the renal cortex.

Thrombosis is a complication of many diseases in veterinary medicine. Heart disease, protein losing nephropathy and steroid therapy or hyperadrenocorticism can all predispose an animal to arterial or venous thrombi. Many of the systemic vessels involved are located in the abdomen and visible on abdominal ultrasound. We can identify thrombosis during an acute episode or as an incidental finding. Here are some of the features you might see.

Appearance of the thrombus

In the acute phase, thrombi in the arterial or venous systems are typically anechoic. These can be caused by migration of a fragment of thrombus from the left atrium to the terminal aorta (such as cats with cardiomyopathy), or a portal vein thrombus that causes portal hypertension and ascites. Acutely formed thrombi are anechoic. You may see some faint echogenicity within the vessel, but these are usually diagnosed using Doppler ultrasound. The color flows around the filling defect in the vessel.

After several days, the thrombus organizes into a visible structure. It is usually intermediate in echogenicity, and can partially or completely fill the vessel (image 2). An older thrombus may contract so that there is flow around it (image 3).

Location of the thrombus

The location of the thrombus determines whether it causes clinical signs. Arterial thrombi, such as in the aorta, can occlude blood flow to distal structures. Ischemia of the hind limbs is a common complication of aortic thrombosis as the thrombus can occlude or extend down the iliac arteries. An aortic thrombus can also occlude the renal arteries causing renal ischemia. The thrombus in image 1 (*) is very close to the renal artery (R) but not occluding it. Portal vein thrombosis is also usually clinical because of the ascites that forms from portal hypertension. Thrombi in the splenic veins are very common, and don’t usually cause any symptoms. These can be an incidental finding (Image 2 and 3), such as in this dog with lymphoma who had been treated with prednisone.

Tumor thrombus

Tumors can also cause physical obstruction of a vessel, usually in the caudal vena cava. Any tumor with a tributary joining the cvc can infiltrate the vessel and reach the systemic venous circulation. The most common tumor that invades the caudal vena cava is an adrenal tumor (image 4), with pheochromocytomas having a predisposition. The tumor thrombus starts by traveling down the phrenicoabdominal vein that runs across the mid-portion of the gland, then reaches the caudal vena cava. Renal tumors can follow a similar pattern and invade down the renal vein.

How to evaluate thrombosis:

• Use color Doppler to look for acute thrombi
• Evaluate the extent and location of visible thrombi
• Check for peripheral flow with color Doppler
• Look for evidence of neoplasia in the region
  
• Check for sequelae of thrombosis such as ischemia of distal structures or ascites

Chronic liver diseases cause damage to the normal liver parenchyma. Eventually, most of the hepatocytes are replaced with fibrous tissue and islands of nodular regeneration. When we see these cases in ultrasound, there are some characteristic changes to look for.

The liver is small and nodular

A small, nodular liver is very typical of cirrhosis. The liver can be very hard to see cranial to the stomach with the dog positioned in dorsal recumbency. A good approach is to use the intercostal spaces on the right and left sides to get cranial to the stomach and closer to the liver. In the first image, you can see the small liver lobes, with the contour distorted by a nodule (arrow).

Signs of portal hypertension

The fibrosis in the liver causes an increase in portal pressure. The portal system is a low-pressure system, with about 0-10 mm of mercury causing blood to flow from the intestines and splanchnic organs toward the liver. When the pressure in the liver rises above this, blood will flow retrograde along multiple extrahepatic shunts that open between the portal system and the caudal vena cava.

The things to look for in portal hypertension are ascites and the multiple extrahepatic shunts themselves. You can see the large amount of anechoic effusion in both images. In the second image, there are transverse and sagittal sections of vessels along the capsule of the kidney. These are multiple extrahepatic shunts, and they tend to form around the left kidney more so than the right. Color Doppler is a good way to demonstrate the vascularity in the region. In some cases, you may see reverse flow in the portal vein or one of its tributaries.

Things to look for:

• small, nodular liver
• ascites
• multiple extrahepatic portosystemic shunts
• hepatofugal flow in the portal vein

After teaching in the introductory ultrasound lab last week, I just want to post some quick tips on how to hold the transducer that several students found helpful.

• Hold the transducer like a pencil, not a flashlight. This gives your wrist the greatest range of motion for moving in different planes.
• Hold the transducer close to the contact surface with the patient. The farther away from the surface you hold it, the more each motion is magnified. Magnified motions make it hard to control the image.
• Let the fourth and fifth fingertips of your scanning hand contact the skin. Here’s a picture of the correct grip using a linear transducer in a person. Keeping your hand in contact with the patient helps keep your hand from sliding away while you are looking at the screen. It also helps keep your hand stable and the image steady.

Everyone has their own pattern for performing an ultrasound exam. It helps to make sure you look at the major organs for signs of disease. In addition to the kidneys, gastrointestinal tract and pancreas, the ileocolic junction is a very important area to examine in cats. Cats are prone to gastrointestinal neoplasia such as lymphoma and adenocarcinoma. Many of these tumors form at or near the ileocolic junction. In addition, the ileocolic lymph nodes can be enlarged in these and other GI diseases.

The ileocolic junction is formed by the junction of the ileum into the ascending colon at right angles. To find the ileocolic junction, start with the right kidney in a sagittal plane (Image 1). Then, slide the transducer medially. The ileum is thicker than other small intestinal loops with obvious wall layering. With it in a sagittal plane, you should see it terminate into a cross-section of the colon (Image 2). The ascending colon will be larger than the ileum, with thinner walls and dirty shadowing from gas and feces. If you can’t see it right away, rotate the transducer 90 degrees to see if you can recognize it. Another option is to find the transverse colon and follow it caudally to the ascending colon and ileum. Once you find the IC junction, examine the area for any enlarged lymph nodes (Image 3). This should become a regular stop in your ultrasound examination.

Cyclophosphamide has been known to induce a sterile, hemorrhagic cystitis in dogs when used in chemotherapy. As ultrasonographers, we are often asked to monitor the response to treatment of this condition. Today I’d like to show you some images of the progression of disease from acute through the healing process.

The first image is a transverse image of the bladder shows the thickened, irregular wall characteristic of cyclophosphamide-induced cystitis when first diagnosed. The mucosa is hyperechoic, which can be caused by hemorrhage. The bladder wall is approximagely 1.4 cm thick.

After two months of treatment, the majority of the bladder wall has returned to normal thickness and echogenicity (image 2). This sagittal image shows residual focal thickening in the dorsal aspect. The echogenicity is more normal, and the mucosal surface is more regular.

Finally, at 5 months (image 3, sagittal), the bladder wall is even and regular with very mild thickening at the cranial pole.

Does anyone else have experience imaging these? Post a comment here.

Medgadget reported on a Siemens handheld ultrasound machine that is the size of a Blackberry. The screen looks pretty small, but it would be interesting to see what it can do. Here is a link to the press release from Siemens, which states

Additional applications include veterinarian medicine.

We all know that there are artifacts on just about every ultrasound image we look at. The physics of the sound waves interacting with tissues is complicated! But many of these artifacts need to be recognized and acknowledged so that you can move on with interpreting the images. The mirror image artifact is one that you’ll see in the cranial part of the abdomen.

Ultrasound images are formed by the transducer producing the beam, and also detecting that beam as it is reflected from tissue interfaces. The transducer calculates how much time has passed since that particular pulse left, and uses the time to place the image at the correct depth on the screen. It always assumes that the ultrasound pulse traveled in a straight line.

Highly reflective, curved surfaces, like the diaphragm, can reflect that pulse of sound in a different direction before it returns to the transducer. So the transducer places that portion of the image deeper than it actually is in the body. In the case of the diaphragm-lung interface, the image gets mapped to the far side of the diaphragm where the lungs are. It can look like there is a diaphragmatic hernia, with liver present in the thorax, or like there is consolidation of a lung lobe. In this example, the liver parenchyma and gallbladder are mirrored into the thorax with the sharp hyperechoic line of the diaphragm separating them.

Last week I wrote about the signs of chronic renal disease in cats. Ultrasound often shows small kidneys that may be irregular, have poor corticomedullary distinction, mineralization or pyelectasia. We see these changes commonly in cats with no or minimal clinical or biochemical signs of renal disease, and they stay quite stable. But acute decompensations occur, causing rising BUN and creatinine, and ultrasound often plays a large part in finding out why.

Ureteral obstruction

Renal disease often affects both kidneys, but can be asymmetric. Cats with chronic renal disease can have one kidney that is larger than the other, that contains more normal looking parenchyma. If one kidney is failing, the other undergoes compensatory hypertrophy to make up some of the lost function. In general, this is the kidney that is performing most of the work. But both kidneys are affected by the same changes, and renal calculi are one of the more common symptoms. These calculi can dislodge from the renal pelvis and obstruct the ureter anywhere along its length.

To diagnose this problem, start by checking the renal pelvis. Pyelectasia, or dilation of the renal pelvis, can be a sign of ureteral obstruction. The renal diverticuli look very distended (the shape of fingers), and the renal papilla looks blunted instead of v-shaped (image 1). You should be able to follow the ureter from the renal pelvis through the retroperitoneal space to the point of obstruction (image 2). It’s still very small, so slow and careful movements are the key to keeping the ureter in view. A high frequency transducer (10-12 MHz) is also helpful in getting the best image. Don’t forget to adjust depth and focal zones.

A ureteral calculus will look like soft tissue or mineral opacity within the ureteral lumen. Sometimes they will shadow (image 2), and sometimes they are too small to cause one. The ureter should go back to normal size (ie not visible) distal to a single calculus. The inflammation can also sometimes cause a hyperechoic halo in the retroperitoneal fat around the kidney(s). This is a subtle finding, so be on the lookout for it (image 1).

You may also find pyelectasia and ureteral calculi in the other kidney. Most often, the smaller obstructed kidney is chronically obstructed, with a greater degree of pyelectasia, or even hydronephrosis. I find that the larger kidney tends to be the acute problem since it has been performing most of the renal function, unless it is larger because of hydronephrosis.

Pyelonephritis

The other acute exacerbation of chronic renal disease to be on the lookout for is pyelonephritis. Cats with calculi or chronic cystitis can develop pyelonephritis that causes decompensation. Again, you are likely to see changes in both kidneys that indicate chronic renal disease. One of the major features of pyelonephritis is pyelectasia. The renal pelvis is dilated, but not to the degree as an obstructed kidney. The renal diverticuli tend to look more pointed than rounded, and the papilla is blunted (image 2). The ureter is usually not traceable past the first few centimeters, though it may be distended all the way to the bladder. You may see some sludge in the renal pelvis or ureter without obstructive calculi (image 3). The hyperechoic halo can also be a sign of pyelonephritis (image 2 and 3).
Kidneys with pyelonephritis also tend to enlarge because of inflammation. This can be hard to tell with kidneys that are already altered in size, but you can compare them to previous measurements if they are available. Hyperechoic or hypoechoic foci in the cortex or medulla can also be a sign of infection. Pyelonephritis can be either unilateral or bilateral.

There are other causes of acute renal decompensation in these cats, but the two listed here are most common, and have the most consistent ultrasonographic signs. Be patient when looking for the signs, and when trying to trace the ureters, to get the most from the ultrasound exam. Some of the signs are common to both diseases and they can be difficult to differentiate. Other imaging options to diagnose ureteral obstruction include an excretory urogram, nephropyelogram, and CT scan.

Chronic renal disease is one of the most common ultrasonographic findings in older cats. If you’re doing ultrasounds on cats, you’re sure to see signs of chronic renal changes on a daily basis. Today I’ll talk about the renal features to evaluate.

The normal kidney

Normal kidneys in cats are oval or bean-shaped. They’re shorter than canine kidneys, but also wider. The left kidney is located caudal to the spleen, and the right kidney is slightly more cranial and deeper when scanning in dorsal recumbency. The length of the kidney should be 3.8-4.4 cm, and the surface is smooth and regular. Compare the echogenicity of the medulla and cortex to the spleen and liver. The order of echogenicity, from hypoechoic to hyperechoic is medulla, cortex, liver, spleen, prostate. Try the mnemonic, My Cat Loves Sunny Places. The cortex should be about twice the thickness of the medulla, and you should be able to differentiate them easily.

Kidney with chronic renal changes

One of the things you’ll hear in describing kidneys with chronic changes is “poor corticomedullary distinction”. If you compare the first image (normal kidney) with the second image, you’ll see that there is less difference in the shade of gray between the cortex and the medulla. The change in echogenicity implies that there is alteration of the composition of the renal tissue. Compare the echogenicity of the cortex to the spleen and/or liver if possible (it can be hard to get them in the same image) since both the cortex and medulla can be affected.
Measure the length of the kidney, and note the surface contour. The second example here is normal in contour and size (scale not shown). Renal infarcts look like wedge shaped, hyperechoic areas when acute (base toward the periphery), and an inward defect when chronic (fibrosis and scarring). They can drastically alter the shape of the kidney.

The second kidney has two other common abnormalities; pelvic dilation and mineralization.

The anechoic area in the distal third of the kidney is the dilated pelvis. This is normally a potential space, with no visible fluid within it. Certain diuretic conditions such as fluid therapy or polyuria/polydipsia can dilate the pelvis minimally, but more than that is pathologic. Kidney with pyelectasia (renal pelvic dilation without loss of renal tissue) may have previous or current obstruction or pyelonephritis.

Mineralization can occur in the pelvis or the parenchyma. In the parenchyma, it is often an irregularly shaped, hyperechoic focus with distal acoustic shadowing. Take care to differentiate this from the arcuate vessels, which are very echogenic, but look like double parallel lines. The second example kidney has some mineralization of the pelvis. You can see the faint acoustic shadow on the left side of the pelvis. The right side of the pelvis is normal echogenic pelvic fat. This can be hard to tell from a pelvic stone that’s at risk for obstructing a ureter.

The end stage kidney

All of the changes above are chronic and progressive. Regardless of the underlying disease, the kidney tissue becomes replaced by fibrous tissue over time. The kidney gets smaller, the cortex often appears equal or greater thickness than the medulla, and eventually they become indistinguishable. A small kidney can be very hard to find, so use your anatomic and vascular landmarks (spleen, aorta, renal artery) if you need to. The last example kidney is barely visible within the surrounding mesentery.

Although ultrasound is able to detect changes in chronic renal disease, it is not highly sensitive. Cats can have significant renal dysfunction without ultrasonographic signs of renal disease. Conversely, many cats cope with their chronic renal disease though they have severe ultrasonographic changes. The history and bloodwork are important in assessing the significance of the findings. These changes are also non-specific, so the underlying mechanism can’t be determined unless a biopsy is performed.

Next week, we’ll talk about a tricky ultrasound examination; the cat with acute on chronic renal failure.

In Ultrasound controls part I, I described the time-gain compensation controls and how they can optimize your image. Once those are set, it’s time to look at the other three controls on the machine; B-mode gain, depth and focal zones. Each of them has a different and important effect on your ultrasound image.

B mode Gain

The standard scanning mode we use in the abdomen is B mode, or brightness mode. The ultrasound waves are reflected and absorbed as they pass through the abdominal tissues, so they are weaker when they return to the transducer. Similarly to the TGC, we need to amplify the signal to a brightness that we can see. The B mode gain adjusts the overall brightness of the image. You’d like to see good contrast between different organs, but not so bright that you start to see echoes in the bladder or gallbladder. In the first image, the gain is set too low. The image is dark, and it’s hard to see the three anechoic areas in the far field. You can see the small hyperechoic spot in the near field because of the inherent high contrast. In the second image, the gain is set too high. The bright echoes in the near field are just noise, or random echoes that have been amplified to high brightness. They have obscured the small hyperechoic spot in the near field. The increased gain has increased contrast in the far field so that the anechoic areas are more visible. Set your gain keeping the contrast between hyperechoic and hypoechoic areas optimal.

Depth

Every ultrasound machine has a scale on one side of the screen that marks your depth of image in cm. The depth control allows you to increase or decrease the depth of the image. For the liver, you need quite a bit of depth, depending on the size of the dog. Here you need to be able to see the entire curve of the diaphragm. When looking at smaller organs, adjust the depth until the organ fills your screen. That way you’ll get the most detailed image of what you are looking at.

Focal zone(s)

Most machines have an adjustable focal zone, which looks like a triangle or other symbol along the depth scale. When the ultrasound beam exits the transducer, it’s a fairly thin slice, but is not a uniform width along the depth of the entire image. It converges at the point of the focal zone, then spreads out wider as it travels distally. The focal zone is the thinnest part of the slice, so you will get the best detail here. Adjust the focal zone to the depth of the area you are looking at.

You can usually add more than one focal zone to your image to increase the resolution. The trade-off here is that the ultrasound machine is now sending out multiple sets of echoes, one with the focus at each of the focal zones. This takes more time, and you will probably start to see “flickering” or slow motion effect on the screen. The frame rate of the image slows enough that your eye can detect the change from frame to frame. Try it on your machine to see the positive and negative effects.

Once you get used to adjusting these controls on a regular basis, it becomes second nature. Optimized controls make a big difference to the quality of your images. If the depth is not adequate, or the focal zone is not at the right level, you could miss a liver or splenic lesion. Besides, we all like to admire a nice ultrasound image!

At our recent ultrasound course, I took an unofficial poll of the participants to see what they found to be the hardest things to learn in abdominal ultrasound. The discipline requires knowledge of anatomy, understanding of ultrasound physics, and hand/eye coordination to master. Here are some of the things they found difficult:

• Seeing subtle structures on the screen like lymph nodes and adrenals
• Learning which way to move the transducer to get something on the screen
• Picturing which plane you are seeing the organs in
• Differentiating blood vessels from lymph nodes
• How to follow a vessel

With practice, everyone improved their technique in most, if not all of these areas. Learning ultrasound takes practice, practice, practice! What do you find difficult? Post your comments here.

The pet food recall has been the primary topic in veterinary related news for several months. The substance identified in the renal tubules of affected animals’ kidneys is melamine, used in fertilizers and plastics. The doses found in contaminated feeds are low, and it’s still unclear whether this is the primary toxin or a component of a chemical reaction that causes renal toxicity. There is mechanical blockage of the renal tubules on pathological specimens. But Barbara Powers, president of the American Association of Veterinary Laboratory Diagnosticians, told USA today that there is more to the story.

There’s something more going on than just the mechanical blockage because you wouldn’t see so much necrosis (cell death) and inflammation. But I don’t know if anyone knows for sure what the mechanism is.

Pet Connection, VIN and many national and state veterinary associations have been keeping constant watch over the latest findings, and distributing the news and advice to pet owners and veterinarians. The veterinary associations are advising the public that their veterinarian will need to perfom tests for renal disease, which may include an ultrasound examination. Both VIN and Pet Connection gathered information on the numbers of sick pets from across the country. It was an example of the power of the internet and its online communities working at a speed much greater than the companies involved, and disseminating information faster than the scientific journals. I hope that we will see more scientific publications in the near future that shed light on the issue. Wikipedia has a summary of the events and links to many related articles.
Recently, I posted on the findings reported by several radiologists on the ACVR listserv. VIN members also posted those findings, along with a report on 4 additional cases that showed increase in renal size and mild increase in cortical echogenicity (1). I had a chance to review the ultrasound exams of the two cases seen at UC Davis. One was a cat with acute renal failure. The main ultrasound finding was that both kidneys were enlarged (almost 5 cm in length) and the cortices were mildly hyperechoic (Figure 1). The second animal was a dog with previous history of renal and cystic calculi. There was no appreciable change in size or echogenicity of the kidneys.

These descriptions suggest that the findings of melamine toxicosis are similar to those of acute renal failure. It’s unclear whether the crystals cause hyperechoic cortices at this point. I encourage veterinarians who have seen additional cases to add their comments to this post so that we all have a better picture of the ultrasonographic signs of melamine toxicosis in dogs and cats.

(1) The discussion is in the Diagnostic Imaging boards, membership required for access.

Update:

Dr. Seiler included images of the left and right kidneys of the case that she evaluated: