+ General Considerations
- Nephroblastoma is an uncommon congenital tumor originating from the metanephric blastema and resulting from abnormal differentiation of the kidney during embryogenesis
- Mixed tumor consisting of blastema, epithelial, and mesenchymal components in various stages of differentiation
+ Biologic Behavior
- Nephroblastoma is a highly malignant tumor
- Nephroblastoma destroys the renal parenchyma by invasion and compression
- Local invasion of adjacent structures occurs if the tumor penetrates the renal capsule
- 65% metastatic rate
- Metastatic sites include the lungs and liver (common), with other sites such as regional and distant lymph nodes, adrenal glands, thyroid gland, pleura, contralateral kidney, and appendicular skeleton
- Caudal vena cava and renal vein thrombosis has been reported in dogs with nephroblastoma
+ Clinical Features
- Nephroblastoma is usually diagnosed in animals < 12 months
- Nephroblastoma is graded as either favorable or unfavorable on the basis of histologic findings
DIAGNOSIS
+ 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
+ Clinical Staging
Staging system, based on the extent of tumor involvement and surgical findings, for nephroblastoma has been developed by the National Wilms' Tumor Study Group
Imaging
+ 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
+ Clinical Staging
Staging system, based on the extent of tumor involvement and surgical findings, for nephroblastoma has been developed by the National Wilms' Tumor Study Group
Treatment
+ 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
+ Chemotherapy and Radiation Therapy
- Surgical resection and chemotherapy is recommended for all stages of nephroblastoma in children
- Vincristine and actinomycin D are recommended for all stages
- Doxorubicin is added for stage II tumors with unfavorable histology and stage III tumors with favorable histology
- Actinomycin D has been used in canine nephroblastoma with partial responses and prolonged survival times
- Neoadjuvant chemotherapy is recommended for large inoperable tumors, bilateral disease, and neoplastic involvement of the caudal vena cava
- Radiation therapy is recommended for stages III and IV tumors with favorable histology and stage II-IV tumors with unfavorable histology
- Principal concerns in children are the effects of chemotherapy and radiation therapy on developing organs as children are more sensitive to the cardiotoxic effects of doxorubicin and radiation therapy can affect development of the lungs and spine
+ Prognosis
- Effective diagnosis, staging, and multimodality therapy has dramatically reduced the morbidity and mortality in children with nephroblastoma
- Poor prognostic factors in children include the presence of bone metastases and tumor spillage during surgery
- Survival times following nephroureterectomy ± chemotherapy ranges from 8 to > 25 months in 4 dogs
RENAL
NEPHROBLASTOMA
Stages
| I | Tumor limited to the kidney and the renal capsule intact. Tumor completely excised |
| II | Extension of the tumor into adjacent structures. Tumor thrombi or vascular extension of the tumor evident. Local spillage of tumor contents, but tumor completely excised and no evidence of residual tumor |
| III | Evidence of tumor extension into hilar or peri-aortic lymph nodes. Diffuse spillage of tumor into the peritoneal cavity during excision. Evidence of tumor in the peritoneal cavity. Local infiltration of vital structures precluding complete resection |
| IV | Evidence of hematogenous spread of the tumor |
| V | Bilateral renal involvement |