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:

We all think of MR as a diagnostic tool to let us look inside the brain for signs of disease. It gives fantastic anatomical detail and contrast between tissues. Functional MR, or fMRI, is becoming a popular tool in investigating how the brain works. It measures changes in blood flow in different regions of the brain as people perform certain tasks. This information allows us to relate function and structure.

Of course, the advertising industry is very interested in how their products affect our brains. Only 50% of ads trigger any response, and they are the ones people like. Does this mean that ads we dislike are more effective? Read the whole story at Analyst Cafe.

Radio Australia’s All in the Mind recently investigated the effects of fMRI on science and journalism. Dr. Jonica Newby, a former veterinarian and broadcaster, contributed to the podcast panel discussion. One of the topics was the news generating potential of these scientific fMRI studies, since people have a fascination with the brain and how it works. Since the science is still in its infancy, what do the results mean? Are science and the media exaggerating the conclusions past the strength of the evidence? It’s worth a read or a listen.

This is a technology we’ll be hearing more about in the media and in scientific journals. It may have applications in veterinary medicine, such as in evaluating the optical pathways in dogs. But the need for general anesthesia in animal patients makes interpreting the brain scans even more difficult. Hopefully we’ll see more research on this in the future.

It’s interesting to see what people are looking for when they land on the Veterinary Radiology home page. In this post, I’ll address some of the more common questions that people want answered about our specialty.

What is a veterinary radiologist?

A veterinary radiologist is a veterinarian who has a veterinary degree, a year of internship, and a three or four year residency in radiology under their belt. Veterinary school is hard enough to get into, and attracts the best and the brightest. Those who want to specialize in radiology have to undergo another round of competitive applications, and years of training to attain specialist status. Someone who is board certified by the American College of Veterinary Radiology or the European College of Veterinary Diagnostic Imaging has had intensive training by other veterinary radiologists. Disciplines include radiology, ultrasound, Computed Tomography (CAT scan or CT), Magnetic Resonance Imaging (MR or MRI), and nuclear medicine. A specialist also has to pass an intensive written and oral exam to become board certified. Veterinary Radiologists have extensive experience in obtaining and interpreting images fof all types. Here is a link to a previous post on what a veterinary radiologist is.

Why use a veterinary radiologist?

If you have a simple problem like the flu, your GP is able to recommend treatment for it. On the other hand, if you have a more serious problem like a badly sprained ankle, your GP will either order an imaging test, like x-rays or MRI, or refer you to a specialist such as an orthopedic surgeon. In either case, a radiologist will read any imaging studies that are ordered. Experience in interpreting these images helps to find problems that might otherwise be missed, recommend further diagnostics, and optimize the treatment plan.

In veterinary medicine, GP’s provide the vast majority of services, and do a very good job of providing routine medical care. It is worth knowing that there are specialists available, such as veterinary radiologists, who have the advanced training to perform and interpret complex imaging studies. There is an insightful post on Dolittler about specialty referrals. Ask your vet if imaging referral is appropriate for your pet.

Is it veterinary radiology or veterinary diagnostic imaging?

When our specialty first started, the major technique available was the x-ray. It used radiation to produce images of the body that saw “inside” the animal in a way never experienced before. Radiographs, or x-rays of our pets give lots of important information about many different diseases, and so the specialty was named.

In the last 20 years, other technologies have allowed us to see inside the animal in different ways. Ultrasound uses sound waves, magnetic resonance imaging (MR) uses the spin of hydrogen atoms, and computed tomography (CT) uses x-rays analyzed by a computer. All of these techniques have expanded the options we have for “looking on the inside”. Proper application of these imaging techniques and interpreting the results require an advanced appreciation of physics and the radiological appearance of disease. Knowledge of disease processes in veterinary medicine has been supported and advanced by these new technologies, so there is a trend to call our specialty “Veterinary diagnostic imaging”. Imaging plays an important role in diagnosing and monitoring treatment in all species of animals. It’s not just x-rays anymore.

Splenic nodules or masses are extremely common findings when ultrasounding the canine abdomen. Nodules are small, circular abnormalities within the spleen that might be hyperechoic (brighter) or hypoechoic (darker) than the surrounding, normal spleen. Nodules are small (less than 4 cm diameter) and masses are larger (greater than 4 cm diameter), but these are descriptive terms. The nodule or mass can also have mixed echogenicity, or both hypoechoic and hyperechoic regions.

There are many benign causes of splenic nodules and masses. These include nodular hyperplasia (extra splenic tissue), extramedullary hematopoesis (blood cell production outside of the bone marrow), granuloma (older inflammatory tissue), hematoma (blood leakage into the spleen), and myelolipoma (fat deposits). Myelolipomas are a bit more characteristic, as they are hyperechoic and surround the splenic veins near the medial surface.

Unfortunately, more serious diseases such as cancer and infarction, though less common, have similar characteristics. With ultrasound examinations, we can not always tell whether a nodule or mass is benign or malignant. If the lesion is large, and distorting the margin of the spleen by bulging outward, we are more likely to think it is a malignant disease. Regarless of the lesion size, the only way get a diagnosis is to perform a fine needle aspirate of the nodule or mass.

Splenic lesions in cats are taken more seriously, as about half of them are benign and half are malignant. Splenic enlargment or any type of focal splenic lesion should be follwed up by a fine needle aspirate in cats.

While aspirates give us the diagnosis in the majority of cases, they are not always successful. The type of lesion we are dealing with determines whether any cells will be available for sampling. In a small lesion, the chances are good that we will get a representative sample. In a large lesion with lots of bleeding, like a hemangiosarcome (cancer) or a hematoma (just blood), the majority of the mass is made of red blood cells, and it can be impossible for the pathologist to tell them apart. The size and imaging characteristis of the mass, as well as the animal’s other test results will help the clinician decide if a recheck of the lesion to monitor growth, an aspirate, or surgery to remove the spleen is the best option.

Ultrasound is very good at detecting splenic lesions, but not specific for determining whether they are benign or malignant. Repeat ultrasound examinations, fine needle aspirates and splenectomy are all options to help determine what the best option is for diagnosis and treatment.

The language of ultrasound

The language of ultrasound is made up of descriptive words to try to form a picture in the reader’s mind. Ultrasound waves are formed in the transducer (the instrument the radiologist applies to the body), and reflect from tissue interfaces that they pass through back to the same transducer. So at every change in tissue type (eg. fat to kidney), some echoes pass through the interface and some are reflected. The reflected ultrasound waves form the image that we see on the screen.

Echogenicity

Because we are dealing with ultrasound waves, the descriptive terms are based in “echogenicity”, or the way the ultrasound wave is reflected back to the transducer. Each tissue type, such as liver, spleen or kidney, has a particular echogenicity in its normal state. In diseased states, the echogenicity of an organ can be altered, either more echogenic (hyperechoic) or less echogenic (hypoechoic) than usual. These observations can help the radiologist to categorize the type of disease process involved.

Echogenicity can be used to describe the tissue in relation to another tissue, or as compared to its normal state. For example, the mnemonic used to teach relative echogenicities is “my cat loves sunny places”. Taking the first letter from each word, the tissues go from hypoechoic to hyperechoic relative to each other. The renal medulla (inner portion of the kidney) is normally more hypoechoic than the renal cortex (outer portion of the kidney), which in turn is more hypoechoic than the liver, spleen and prostate. Echogenicity is not something that can be measured like ounces or centimeters, so using relative terms makes sense. In the image, the medulla of the kidney (*) is darker, or hypoechoic to the cortex of the kidney (^). The spleen (#) is hyperechoic to both of these tissues.

Echogenicity can also be used to mean “different than the normal echogenicity”. We usually try to compare a tissue to another normal tissue on the ultrasound screen, but it’s not always possible. The radiologist has a mental library of many images of normal tissue echogenicity, and will use that to compare the tissue on the screen as well.

What does it mean?

What does this mean for the animal being imaged? Ultrasound can give us very good information about problems within organs like the liver or spleen, such as picking up nodules (less than 4 cm diameter) or masses (greater than 4 cm diameter). It can also detect generalized changes in echogenicity of an organ.

For example, an enlarged, hyperechoic liver is brighter than the spleen. This can be caused by steroid administration, diabetes, or several other diseases. If there are nodules or masses that are hypoechoic to normal liver, hyperechoic, or mixed, we know that there are focal lesions but not what they are. The description helps a reader to “see” the lesion, but may not be specific to a particular disease. A hypoechoic lesion could be benign liver hyperplasia, which is very common in older dogs, or a cancerous nodule. Certain patterns, such as a “target” lesion, are more associated with cancer. If the diagnosis is unclear after ultrasound, a fine needle aspirate or biopsy might be recommended to determine what the nodule is.

Normal relationships in echogenicity of organs means that there is no apparent problem. If there are no nodules or masses, and the echogenicity of the organ is normal, we are more confident that there is no disease present. Ultrasound does have limitations in detecting disease; especially in the liver, spleen and kidneys, it may not detect subtle changes.

The take-home message

If your animal has an ultrasound examination, changes in echogenicity can help to pinpoint the organs that are affected. The pattern of change can suggest a range of problems, and is often not specific. Your radiologist and veterinarian will consult and determine the next step in diagnosing your animal’s illness. That may include blood tests, a fine needle aspirate or biopsy, or other diagnostic tests. Ultrasound is a very good tool to direct the diagnostic pathway.

Ultrasound terms:

• Hyperechoic – more echogenic (brighter) than normal
• Hypoechoic – less echogenic (darker) than normal
• Isoechoic – the same echogenicity as another tissue

How can we help you with more information?

Are you looking for help interpreting your ultrasound report? There are many services that might be able to help, such as asking a doctor online, or radiology second opinions. As always, talk to your doctor or veterinarian.

Melamine has been identified in the recalled pet food, as well as in the urine and kidneys of an affected animal. The chemical, used in plastics, has been found in the contaminated gluten used in wet pet foods. However, there may have been contamination of dry foods as well. You can read more about it at Pet Connection, where the most recent updates are being posted. An article at the Associated Press summarizes the current situation.

The ultrasound findings in cats and dogs affected with renal failure were originally attributed to Aminopterin. The preliminary findings are listed in this post from last week. It is still unclear which toxin is responsible for the deaths of so many pets, but the source of the contaminated gluten has been identified.

Some of you finding this site might be wondering what exactly a Veterinary Radiologist is. There are actually many specialties in Veterinary Medicine that are similar to those in human medicine, like Radiology, Medicine, Surgery, and Emergency and Critical Care. All diplomates of the American College of Veterinary Radiology have been trained for 3-4 years after graduating from veterinary school, and have passed an exam giving them specialist status (DACVR). The European College of Veterinary Diagnostic Imaging certifies Veterinary Radiologists in Europe (DECVDI). The ACVR also certifies veterinarians who specialize in radiation therapy for animals with cancer, which is called radiation oncology.

Veterinary Radiologists are experts in interpreting radiographs (x-rays), ultrasound, computed tomography (CT), magnetic resonance (MR) and nuclear scintigraphy in animals. Radiology is an essential, non-invasive part of many medical workups in animals, from a chest x-ray to check the size of the heart, to an abdominal ultrasound to look for an intestinal foreign body. We are part of the team of veterinary professionals that can contribute to an animal’s care. Research is an important part of our quest to expand the boundaries of what we know about diagnostic imaging and treatment at veterinary schools and in private practice.

Veterinary Radiologists are available to support your veterinarian in performing and interpreting imaging studies. Find out more at the American College of Veterinary Radiology pages for owners.