GENERAL CONSIDERATIONS

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 Behaviour

•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

•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

•uremia may result from obstruction of urinary outflow, bilateral renal tumors, or age-related renal failure

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

•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 unilateral tumors

•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