Ultrasound of the Urinary System

Presenter: Dr Robert Williams B.Vet.Med. Member of the Australian College of Veterinary Scientists (M.A.C.V.S) Emergency and Critical Care

Finding your way around the urinary system using ultrasound can be an incredibly useful skill and anyone who uses ultrasound in practice should not miss out on last week’s veterinary webinar covering this very topic. Dr Williams has previously led some excellent webinars discussing other areas of ultrasound, and last week’s was no exception to the relevant and in depth information delivered.

Ultrasound of the right and left kidney was the first area visited by Dr Williams. Finding their location is relatively simple but measuring and interpreting their size accurately can prove more difficult. Good dorsal, sagital and transverse views of the kidney are necessary to obtain accurate measurements but this can be tricky as the body’s orientation often does not correspond to that of the kidney and makes accurate positioning difficult. Dr Williams went into great depth explaining how to achieve accurate views of the kidney in each plane, but once you have obtained accurate measurements, how can you decide whether the size of a kidney is normal or abnormal?

Dr Williams explained that figures cited for normal kidney size vary enormously between texts and breeds. A ‘comparison’ approach may offer more relevance and Dr Williams suggests comparing the length of the kidney with the diameter of the aorta. A ratio of less than 5.5:1 would indicate the kidney is small and a ratio of greater than 9:1 would indicate the kidney is enlarged.

Dr Williams also explained that ultrasound of the kidney can show many non-specific changes which indicate disease. For example the presence of an extremely bright hyperechoic cortex in a Sharpei can be a strong indicator of amyloidosis, and the same can be said of a cat with ethylene glycol toxicity. There are also characteristic signs seen in other diseases such as chronic renal failure, where one might expect to find the loss of definition to the cortico-medullary junction, a dilated renal pelvis and shrunken nodular kidneys. However in acute renal failure there are often no changes to the structure of the kidney, and colour Doppler would be necessary to show an increase in blood flow often associated with ARF.

Neoplasia such as lymphoma within the kidney can also be seen as a nodular mass but a diagnosis can only be confirmed by either an FNA or biopsy with a sample ideally being taken from the margin of a lesion. Renal cysts are seen as thin walled anechoic structures which do not alter when the gain on the ultrasound machine is increased. The use of Doppler can also demonstrate the lack of blood flow through a cyst.

Ultrasound of the urinary bladder was also discussed by Dr Williams giving useful tips on interpretation of findings. For example differentiating blood clots from uroliths can be difficult as both are dependant and both create shadow artefacts. Dr Williams recommends repeating the ultrasound in 3-4 days where, in most cases, the blood clot will have dispersed whereas a urolith would still be present. Polyps and transitional cell carcinomas (TCC) can also appear similar but Dr Williams advises that polyps tend to be found in the body of the bladder and TCC’s are found in the neck often having a cauliflower appearance. Once again biopsies are necessary to confirm a diagnosis and Dr Williams highly recommends a technique using a urinary catheter which is explained within the webinar.

Dr Williams has provided an information-packed veterinary webinar with the visual element of this webinar being crucial to understanding the techniques used in ultrasound of the urinary tract. Unfortunately this blog cannot enlighten you on the visual aspect which can only be achieved by logging into ‘The Webinar Vet’ and taking an hour of your time to watch this excellent webinar.

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