+ General Considerations

• Renal cystadenocarcinoma is an autosomal dominant condition in GSD with a genetic linkage to chromosome 5
• Renal cystadenocarcinoma represent 6% of all renal tumors in GSD
• Renal cystadenocarcinoma has also been described in a GSD-cross dog and Golden Retriever
• Renal cystadenocarcinoma is a bilateral disease with slowly progressive deterioration of renal function
• Renal cystadenocarcinoma is associated with nodular dermatofibrosis and uterine leiomyoma
• Nodular dermatofibrosis is present in all cases and appear as small, firm, and mobile subcutaneous masses

+ Biologic Behavior

• Clinical signs are worse with bilateral disease and the size of skin and uterine tumors increase with advancing age
• Metastasis reported in up to 47% of cases:
• Metastatic sites including sternal and abdominal lymph nodes, liver, lungs, pleura, and peritoneum
• Metastasis is more common with large, solid, and poorly differentiated tumors
• Main causes of death are renal failure, metastatic disease and secondary skin infections

+ Clinical Signs

• Clinical signs are non-specific such as abdominal enlargement and abdominal pain
• Urinary signs are uncommon
• Skin lesions (i.e., dermatofibrosis) are associated with renal cystadenocarcinomas in GSD
• Lameness caused by either skeletal metastases or hypertrophic osteopathy

+ Urinalysis and Urine Sediment Cytology

• Proteinuria is a common finding with renal tumors
• Hematuria is uncommon
• Urine sediment cytology is rarely diagnostic for renal tumors

+ Blood Tests

• Hematology and serum biochemistry findings are usually normal or non-specific
• Mild-to-moderate normochromic, normocytic anemia can be caused by either hematuria or bone marrow suppression secondary to chronic disease
• Polycythemia is a reported paraneoplastic syndrome with renal tumors
• Uremia may result from obstruction of urinary outflow, bilateral renal tumors, or age-related renal failure

+ General Considerations

Survey abdominal and thoracic radiographs, contrast radiography, ultrasonography, CT, and MRI are imaging modalities used to identify the presence and extent of renal tumors

+ Survey Abdominal Radiography

• Survey abdominal radiographic findings: sublumbar lymph node enlargement, renomegaly, and skeletal metastases, especially lumbar vertebrae and pelvis
• Abdominal mass is identified in 81% and localized to the kidney in 54% of dogs with primary renal tumors
• Focal mineralization can be observed but difficult to differentiate tumor from renal calculi and GI opacities

+ Excretory Urography

• Excretory urographic findings: space occupying renal mass, variable opacification of the renal parenchyma, and distortion of the renal pelvis
• Excretory urography successfully identifies a renal mass in 96% dogs with primary renal tumors

+ Ultrasonography

• Ultrasonography results in earlier diagnosis and more successful treatment of renal neoplasia in humans
• Renal tumors, except for LSA, produce a mixed echogenicity with disruption of the normal renal architecture
• Renal LSA is usually hypoechoic
• Ultrasonography is also useful in detecting neoplastic involvement of regional lymph nodes and adjacent structures such as the adrenal glands ± caudal vena cava

+ Advanced Imaging

• CT scans are used for the diagnosis and local staging of renal neoplasia with a high correlation between CT findings and gross pathology
• MRI is preferred for identifying adjacent vascular and visceral invasion, especially if renal-sparing surgery is planned
• Other imaging techniques include caval venography and nuclear scintigraphy

+ Biopsy

• Biopsy is required for definitive diagnosis of renal tumors
• Biopsy techniques: FNA, needle biopsy, and wedge biopsy
• FNA and needle-core biopsy can be performed using a blind, ultrasound-guided, laparoscopic, or open technique
• Ultrasound-guided biopsy is a rapid, safe, and accurate technique for diagnosing focal and diffuse renal disease
• Blind percutaneous needle biopsy can be performed in cats where the kidney can be immobilized by palpation
• Percutaneous biopsy should be performed with bilateral renal lesions or suspected renal LSA
• Single procedure surgical biopsy, staging, and definitive treatment preferred for unilateral lesions
• Complications of needle biopsy: minor localized hemorrhage, microscopic hematuria, and tumor seeding

+ Surgery

• Surgical management depends on behaviour of the tumor, presence of metastases and bilateral renal involvement, and invasion of the caudal vena cava and adjacent structures
• Nephroureterectomy is recommended for:
• Malignant renal and ureteral tumors except LSA
• Grading and staging of nephroblastoma
• Nephron sparing techniques should be used for benign tumors and bilateral disease to reduce the risk of renal failure