CT of the canine kidneys for renal masses and upper urinary tract disease

Why a renal mass needs a full work-up

Primary renal tumours are uncommon in dogs, but they are usually malignant. In a multi-institutional series of 82 dogs (Bryan et al., Journal of Veterinary Internal Medicine, 2006), 49 had carcinomas, 28 sarcomas and 5 nephroblastomas. Tumours occurred with equal frequency in each kidney, and 4% were bilateral. Common signs were:

• haematuria
• inappetence, lethargy or weight loss
• a palpable abdominal mass

Pulmonary metastases were seen on thoracic radiographs in 16% of dogs at diagnosis, and 77% had metastatic disease at the time of death. The authors concluded that surgery was the only treatment that improved survival. Staging before surgery therefore matters as much as describing the mass itself.

When CT is indicated

Contrast CT is worth discussing when:

• ultrasound finds a renal mass and surgery is being considered
• both kidneys are abnormal
• the cause of haematuria or a dilated renal pelvis remains unclear

What CT shows in renal tumours

Two retrospective studies describe the CT features of canine renal tumours. In a 2026 study of 32 dogs (Occhiuzzi et al., American Journal of Veterinary Research), the diagnoses were renal cell carcinoma (12), metastatic lesions (10), multicentric lymphoma (5), sarcoma (2), and one each of haemangiosarcoma, primary lymphoma and cystic adenoma. The second was a smaller study of 15 dogs (Tanaka et al., PLOS ONE, 2019).

CT feature	Points towards	Seen in
Single unilateral mass, heterogeneous enhancement, tumour vessels in the corticomedullary phase	Renal cell carcinoma	32-dog study, 15-dog study
Collateral vessels around the mass	Renal cell carcinoma more than lymphoma or metastases	32-dog study
Bilateral nodules	Multicentric lymphoma or metastases	32-dog study, 15-dog study
More homogeneous enhancement	Lymphoma	32-dog study, 15-dog study
Unilateral mass with a non-enhancing area	Haemangiosarcoma, in a small number of dogs	15-dog study

These patterns help rank the differentials, but they overlap. In the larger study, overlap between tumour types reduced specificity. In the smaller study, the differences between renal cell carcinoma, lymphoma and haemangiosarcoma were not statistically significant.

Other kidney findings on contrast CT

Not every renal defect is a tumour. In 826 dogs that had abdominal contrast CT (Sutthigran et al., Journal of Veterinary Internal Medicine, 2022), kidney infarction was found in 3.15% (26 dogs). Of the 56 lesions:

• most involved less than 25% of the kidney (47 of 56)
• most were at the caudal pole (31 of 56)
• the sagittal plane showed them best

Stones and obstruction in the upper urinary tract

In 14 dogs with ureteral stones (Kaufmann et al., New Zealand Veterinary Journal, 2026):

• stones were bilateral in 4 dogs
• 10 dogs had two or more stones
• twelve dogs had pyelectasis
• calcium oxalate was the most common composition

Kidney CT protocol at a glance

The 32-dog and 15-dog renal tumour studies each used one contrast CT examination to assess the kidneys, the regional lymph nodes and the lungs. For the ureters, CT excretory urography is used. In 14 healthy dogs, adding furosemide (Secrest et al., Veterinary Radiology & Ultrasound, 2013) increased the number of ureteral segments seen and their diameter on the earlier post-contrast images; the later images gave no advantage.

What the radiologist looks at

• Mass or nodules? A single unilateral mass points towards renal cell carcinoma, bilateral nodules towards lymphoma or metastases. Because the patterns overlap, they rank the differentials rather than give a diagnosis.
• Collateral vessels. They were significantly more frequent in renal cell carcinoma than in multicentric lymphoma or metastases, and were associated with mass rather than nodular lesions. The authors recommend considering them in surgical planning.
• Renal vein and caudal vena cava. In one reported dog (Murakami et al., Canadian Veterinary Journal, 2026), contrast CT showed a tumour thrombus extending about 1.5 cm from the right renal vein into the caudal vena cava, with no distant metastasis. This allowed a planned nephrectomy and caval thrombectomy. Caval extension is worth stating explicitly in every renal mass report.
• Lymph nodes and lungs. Lymphadenopathy and pulmonary metastasis are assessed in the same examination as the kidneys.
• Infarct or tumour? In the 826-dog study, most infarcts involved less than 25% of the kidney and sat at the caudal pole, best seen in the sagittal plane.
• Both ureters, along their full length. Stones were bilateral or multiple in many dogs. Normal ureteral peristalsis causes intermittent and inconsistent filling, so a segment that is not opacified is not automatically obstructed.

What your report will include

Every Veheri case is read by a radiologist or neurologist, and when you order you can choose Diplomate-only reporting or the full specialist panel. You can chat directly with the specialist assigned to your case, and a simplified pet owner report helps you explain the findings to the owner.

When you take the report forward:

• CT does not give a histological diagnosis. CT features overlap between tumour types, so tissue sampling is usually still needed where the result will change treatment.
• Urinalysis after contrast can mislead. In 30 dogs (Barthe et al., Journal of the American Veterinary Medical Association, 2026), iodinated contrast for CT increased median urine specific gravity from 1.046 to 1.058 and urine pH from 6.25 to 7. Sediment, dipstick and protein-to-creatinine ratio were unchanged. If specific gravity or pH matters, collect urine before contrast or on another day.
• Talking to the owner: in the 82-dog series, surgery was the only treatment that improved survival, and 77% of dogs had metastatic disease by the time of death. The staging findings belong in that conversation.

What to include when you request a renal CT report

• signalment: age, breed and sex
• the ultrasound findings and which kidney is affected
• haematuria, abdominal pain, palpable mass or weight loss
• serum creatinine, urinalysis and the time it was collected relative to CT
• previous thoracic imaging
• whether surgery is planned, so vascular anatomy and caval extension are described

How Veheri can help

Veheri provides veterinary teleradiology for X-ray, CT and MRI, with expert support for CT scanning protocols, positioning and acquisition. Related reading: CT excretory urography for ectopic ureters in dogs, CT of adrenal masses in dogs and oncology imaging for staging and planning.