One of the primary distinguishing features between veterinary and human medicine is how much smaller veterinary patients can be. As veterinarians know, minute size often means a rapid and dangerous impact of any threats to the animal’s health and challenges with treatment, particularly surgery, on intricate anatomical systems. This is especially true for conditions, such as vascular anomalies, which must be detected and remedied in canine patients during the first few months of life or when they are still in the early stages of growth. Finding and treating these anomalies require precision. Therefore, veterinarians must know what to look for and have the right diagnostic imaging equipment to find it. There are three common kinds of vascular abnormalities in puppies that will be detailed in this article: shunts, patent ductus arteriosus (PDA), and persistent right aortic arch (PRAA). Shunts Symptoms indicating a shunt’s presence are noticeable early in life. Lethargy is a common trait of puppies with shunts. These dogs will also present with digestive issues, such as vomiting or diarrhea, often leading to delayed development. Increased thirst and urination are also indicative of a shunt, as well as blood appearing in the animal’s urine. Shunts are caused by a birth defect when a puppy is born with too many vessels formed in or around the liver. Blood from the portal system abnormally detours around the liver and instead returns to the heart by entering the systemic venous drainage in a number of different patterns (Figures 1A and 1B). Black-and-white 3D images of a portosystemic shunt (1A) and a splenoazygos shunt (1B). Photo courtesy Imaginalis PDA PDA is similar to shunts in that an extra blood vessel is present at the time of birth. Like with shunts, digestive issues are an indicator of PDA, as are respiratory signs such as labored breathing and low stamina. Murmurs are another common sign that a puppy may have a PDA. It is also more common in show breeds, such as Pomeranians, Maltese, and Spaniels than in Labradors and mixed breeds, which can further assist veterinarians in making an accurate diagnosis. However, PDAs refer more specifically to the connection between the aorta and pulmonary artery. This connection should close in early development, but in puppies with a PDA it remains open after birth. Blood is then recirculated through the heart instead of reaching other organs, which, if left untreated, can lead to heart failure. PRAA Another condition that can be seen in puppies is a PRAA, also known as a vascular ring anomaly (Figure 2). Birth defects also cause these and result in partial or complete rings forming around and squeezing the esophagus, trachea, or sometimes both. As the puppy grows, this issue becomes more apparent. Figure 2. Evidence of a persistent right aortic arch (PRAA) in a one-month-old poodle puppy. Photo courtesy Imaginalis The impact of these rings around the esophagus is not usually noticed until a dog starts eating solids, when the restriction often causes regurgitation of undigested food. Pressure also increases on the trachea as the dog gets bigger, leading to audible breathing problems. This condition is the most disruptive of the three. An example of its impact was seen when a one-month-old poodle puppy was brought in because it was vomiting after every meal and was noticeably underweight compared to the rest of the litter. Diagnostic imaging found compression on her trachea and esophagus that would continue to impact her health. The condition would likely prove fatal if left untreated. Getting a clear picture Due to the dire nature of all three conditions, early detection is key. When any of them are suspected, veterinarians should complete specific lab work before moving to diagnostic imaging and ultimately treating with surgical or minimally invasive intervention. Historically, ultrasound has been one of the primary options for detecting vascular abnormalities. However, several shortcomings make it less than ideal. Since most of the patients screened for these conditions are puppies, the probe can occasionally be larger than the animal’s chest, especially in toy breeds. These abnormalities are complex and can be mistaken for other veins or arteries. Deriving effective results from studies is dependent on the animal patient, anomaly, and sonographer skill level. A CT scan is the recommended imaging modality for detecting vascular anomalies. One scan of the animal should be taken without contrast to establish a baseline. Then a second scan should be taken once contrast has been injected. With these two images for reference, veterinarians should notice the presence and location of any shunts, PDAs, or PRAAs. While most veterinarians know what CT is and how to apply it in a clinical setting for these applications, they may not know that there are three different kinds of CT that each perform differently in a vascular anomaly scenario. 1) Cone beam Cone beam has been a mainstay imaging method for decades. Even as more advanced technologies are developed, it remains the best choice for certain applications. As the name would suggest, cone beam CT scanners use a cone-shaped X-ray to create images. These machines are often used in both human and veterinary dental applications to create a full rendering of a patient’s jaw, teeth, and skull to detect any abnormalities. Of the three kinds of scanners, cone beams use the smallest amount of power, only 5 kilowatts, and therefore achieve the lowest penetration level. A medium-to-large canine skull is the largest system one of these machines can image. In addition to the size limitations, cone beam CTs provide images at lower contrast resolution than other options on the market. Neither of these issues are a problem in dentistry, as the required image size is within cone beam’s parameters, and the resolution needed for detecting contrast is low. This cements cone beam’s utility as a reliable and relatively cost-effective solution for these applications. However, for general practice, screening of larger regions, such as lungs and abdomens, is often required. Image quality can also be a concern for vascular abnormalities, as a higher resolution is needed to differentiate a puppy’s trachea from the tiny ring wrapped around it. 2) Helical (also known as spiral, conventional, or multislice) CT scanning has undergone six generational revisions, starting with a slow single helical slice orientation to faster 256 multislice configurations. The patient lies flat and passes through the gantry as a pencil-thin X-ray beam rotates, taking hundreds of images. Those images capture individual “slices” of the patient’s anatomy that are then reformatted into different views. The slices can also be stacked and put back together to form a 3D model. While helical CT provides higher resolution and size capabilities than cone beams, it is not without its own limitations. Bringing these machines into a veterinary clinic requires significant and often expensive modification to account for cooling the system down and its necessary footprint. As with cutting up and reassembling any other items, slicing and stacking diagnostic images can also leave tiny gaps in the final scan. Often, those missing pieces are inconsequential, but for vascular abnormalities that can easily be mistaken for normal anatomy, every detail is critical. 3) HDVI High-definition volumetric imaging (HDVI) technology is the most recent addition to the world of veterinary CT. The HDVI CT may appear similar to helical CT, as both machines will automatically move patients through the gantry as images are captured. HDVI may also be mistaken for cone beam CT simply because it uses a flat panel receptor, like cone beam systems do. In reality, HDVI combines the best features of both systems with its own additional capabilities to optimize CT imaging capabilities for general practice. HDVI scans detect soft tissue detail in chest and abdomen scans at a higher resolution than cone beam CT scanners in animal patients. With its use of a table and gantry, HDVI offers more size flexibility and can be used to capture images in chests and abdomens in canine patients up to 180 lbs. Helical CT can generally get down to around 600 microns, but that often requires thinner slice images. This can increase the overall dose to a level of radiation that is considered an overdose to many small animal patients. In some cases, such as detecting vascular abnormalities in puppies, extra distinction between anatomical components is needed. Investing in the higher resolution and less modification to the facility can be worth it to equip veterinarians with the most complete imaging information available, giving them the tools they need to achieve the best possible patient outcomes. Selecting a scanner Most veterinary practices will only purchase one CT scanner for their operation. The decision comes down to determining which one best fits their facility, their budget, and other needs tailored to their collective skillsets. If companion animal clinics want to concentrate only on dentistry imaging applications and other needs that require low soft tissue resolution, they generally gravitate to cone beam. Veterinary practices with internal medicine and surgery specialists have historically opted for the helical CT scanner, with many purchasing used units from human hospitals. If a veterinary team is concerned with infrastructure such as cost, cooling, and footprint, or wants to perform more diagnostic and treatment services in-house, like diagnosing and treating vascular abnormalities, HDVI can be a viable solution for many different uses in animal patients. Vascular abnormalities can be debilitating for the puppies they impact. However, in most cases, they are the only obstacle standing in the way of that animal living a normal life. For example, after a veterinarian detected a PRAA on an HDVI CT scanner (Figure 3) and surgically removed it from a one-month-old poodle puppy, the patient caught up to the rest of the litter and is now living a normal life. Figure 3. A PRAA detected by an HDVI CT scanner. Photo courtesy Imaginalis The surgery required to remove any of the three abnormalities is intricate, especially with a PRAA, given its proximity to the esophagus and trachea. A complete, detailed image of the issue empowers veterinarians to perform surgery to the best of their ability and send as many patients as possible off to healthier lives. With nearly three decades in the animal health industry, Robert Whitaker is an experienced animal imaging technician and veterinary business professional. Whitaker has contributed to advancing imaging in food animal, large animal, and small animal applications since 1995. He is the business development director for veterinary in North America at Imaginalis. Craig Glaiberman, MD, is a vascular and interventional radiologist with over 25 years of experience in the medical field. He graduated from the University of Texas Health Sciences Center at San Antonio School of Medicine and serves as the chief medical officer for Imaginalis.
