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Wilms tumor is the most common primary renal malignancy in children, typically presenting as an asymptomatic abdominal mass in children under 5 years of age. This embryonal tumor arises from primitive metanephric tissue and accounts for approximately 90% of pediatric kidney cancers. Early diagnosis and multimodal treatment including surgery, chemotherapy, and sometimes radiation therapy result in excellent cure rates exceeding 90% in most cases.
Wilms tumor develops from abnormal proliferation of metanephric blastema, the embryonic tissue that normally differentiates into mature kidney structures during fetal development. The tumor is associated with mutations in several genes including WT1, WT2, and β-catenin, which normally regulate nephrogenesis and cellular differentiation. Loss of these tumor suppressor functions leads to uncontrolled growth of primitive renal tissue, forming a heterogeneous mass containing blastemal, epithelial, and stromal elements.
The diagnostic approach focuses on imaging studies, particularly ultrasound and CT/MRI, to characterize the renal mass and assess for metastatic disease, while avoiding biopsy due to risk of tumor rupture and staging implications. Clinical staging determines treatment intensity, with factors including tumor size, capsular invasion, lymph node involvement, and presence of favorable versus anaplastic histology on surgical specimen. The differential diagnosis includes other pediatric abdominal masses such as neuroblastoma, hepatoblastoma, and renal cell carcinoma, which can be distinguished by imaging characteristics, tumor markers, and age of presentation.