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:
I had the opportunity to scan a research cat who had been fed the contaminated food previously. At time of presentation the azotemia had already resolved (the diet was stopped two weeks previously I believe). The kidneys were irregular in shape with cortical infarcts. Both kidneys had indistinct corticomedullary definition with a faint hyperechoic corticomedullary rim and mild pyelectasia. Renal size was normal. RI was increased with 0.75 on the right and 0.70 on the left.
Gabriela Seiler, University of Pennsylvania