Pathology

Wilms' tumor is derived from primitive metanephric blastema and is characterized by histopathologic diversity. The classic Wilms' tumor is composed of persistent blastema, dysplastic tubules (epithelial), and supporting mesenchyme or stroma.

Table 19-4. Investigations in Wilms' Tumor

History: family history of cancer, congenital defects, and benign tumors

Physical examination: congenital anomalies (aniridia, hemihypertrophy, genitourinary anomalies), blood pressure, liver enlargement Complete blood count: presence or absence of polycythemia Urinalysis

Blood chemistries: blood urea nitrogen, creatinine, uric acid, serum glutamic-oxaloacetic transaminase, serum glutamic pyruvic transaminase, lactic dehydrogenase, alkaline phosphatase

Assessment of coagulation factors: prothrombin time, partial thromboplastin time, fibrinogen level, bleeding time (if abnormal, factor VIII level, von Willebrand factor antigen level, factor VIII ristocetin cofactor activity)" Assessment of cardiac status: electrocardiogram and echocardiogram in all patients who receive Adriamycin; echocardiogram may be useful in detecting the presence of tumor in the right atrium Abdominal ultrasound

Abdominal CT scan with special attention to: Presence and function of the opposite kidney Evidence of bilateral involvement Evidence of involvement of blood vessels with tumor Lymph node involvement Liver infiltration Chest radiograph (posteroanterior and lateral)

Chest CT scan: helps recognize small metastases that may be hidden behind ribs, diaphragm, and heart and may be missed on chest radiograph Skeletal scintigram: only in cases of clear-cell sarcoma—bone-metastasizing renal tumor of childhood

Magnetic resonance imaging and/or CT scan of brain: only in cases of rhabdoid tumors, which are frequently associated with CNS tumors, and clear-cell sarcoma of the kidney, which may metastasize to the brain Peripheral blood for chromosomal analysis: in cases of congenital anomalies, such as aniridia, Beckwith-Wiedemann syndrome, hemihypertrophy

"To exclude associated acquired von Willebrand disease.

Table 19-5. Clinicopathologic Staging System"

Stage Description

I Tumor limited to the kidney and completely excised: The surface of the renal capsule is intact. The tumor is not ruptured before or during removal or has been biopsied. No residual tumor apparent beyond the margins of excision.

II Tumor extends beyond the kidney but is completely excised: There is regional extension of the tumor (i.e., penetration through the renal capsule into the perirenal soft tissues). The vessels of the renal sinus are not involved nor is there extensive invasion of the renal sinus. Vessels outside the kidney are infiltrated or they contain tumor thrombus. The tumor may have been biopsied or there has been local spillage of the tumor confined to the flank. No residual tumor is apparent at or beyond the margins of excision.

III Residual nonhematogenous tumor confined to the abdomen: Any of the following may occur:

A. Involved lymph nodes (on biopsy) in the hilus, the periaortic chains, or beyond6

B. Diffuse peritoneal contamination by the tumor due to spillage of tumor beyond the ipsilateral flank before or during surgery, or tumor growth that has penetrated the peritoneal surface

C. Tumor implants found on the peritoneal surfaces

D. Gross or microscopic tumor remains postoperatively (e.g., tumor cells are found at the margin of surgical resection on microscopic examination)

E. Tumor not completely resectable because of local infiltration into vital structures.

IV Hematogenous metastases: Metastases extend beyond those seen in stage III

V Bilateral renal involvement at diagnosis: An attempt should be made to stage each side according to the preceding criteria on the basis of extent of disease prior to biopsy.

aEach case should be characterized according to favorable and unfavorable histology.

•"Lymph node involvement in the thorax or other extra-abdominal sites would be criteria for stage IV.

The coexistence of epithelial, blastemal, and stromal cells has led to the term triphasic to characterize the classic Wilms' tumor. Each of the cell types may exhibit a spectrum of differentiation, generally replicating various stages of renal embryogenesis. The proportion of each cell type may also vary significantly from tumor to tumor. Some Wilms' tumors may be biphasic or even monomorphous in appearance.

Clear cell sarcoma of the kidney and rhabdoid tumor of the kidney are not Wilms' tumor variants.

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