ETIO-PATHOGENESIS OF WILMS TUMOR
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MORPHOLOGIC FEATURES
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Most nephroblastomas are unilateral, being bilateral in less than 5% of cases, although patients with Denys-Drash syndrome mostly have bilateral or multiple tumors. They tend to be encapsulated and vascularized tumors that do not cross the midline of the abdomen. In cases of metastasis it is usually to the lung. A rupture of Wilms' tumor puts the patient at risk of hemorrhage and peritoneal dissemination of the tumor. In such cases, surgical intervention by a surgeon who is experienced in the removal of such a fragile tumor is imperative.

Wilms' tumor is a malignant tumor containing metanephric blastema, stromal and epithelial derivatives (triphasic nephroblastoma).
Pathologically, a triphasic nephroblastoma comprises three elements: blastema= diffuse, nodular, cordlike or basaloid pattern of densely packed primitive small blue cells with scanty cytoplasm, overlapping nuclei with finely dispersed chromatin mesenchyme= include cells showing rhabdomyoid differentiation epithelium= fibroblast-like stroma and epithelial elements (abortive tubules, glomeruli with elongate / ovoid nuclei having molded / wedged shapes)

The tumor may have heterologous epithelial and stromal elements including smooth muscle, cartilage, adipose tissue, squamous or mucinous epithelium, bone and neural tissue; prominent skeletal muscle is associated with bilateral tumors in young children. The tumor is compressing the normal kidney parenchyma.

Figure 1. Triphasic tumor. The triphasic nature of Wilms Tumor is obvious here. The epithelial elements surround nodules of blastema and are attempting for form rosettes. The nodules of