The gross specimen of the kidney shown above reveals a large, well-demarcated mass. This appearance is most characteristic of which of the following pediatric renal tumors?

Explanation

## Image Findings * **Large, solitary, well-demarcated mass** occupying a significant portion of the renal parenchyma. * **Pale tan-white to greyish-white cut surface** of the tumor. * **Heterogeneous appearance** with areas of softer, yellowish-brown tissue, suggestive of necrosis or myxoid change. * **Compression and distortion** of the adjacent normal renal parenchyma. * No prominent hemorrhage or large cystic degeneration is evident. ## Diagnosis **Key Point:** The image shows a **Wilms tumor (nephroblastoma)**, characterized by a large, well-demarcated, tan-white, heterogeneous mass compressing normal renal tissue. Wilms tumor is the most common primary malignant renal tumor of childhood. Grossly, it typically presents as a large, solitary, well-circumscribed mass, often with a variegated cut surface that can include areas of tan-white firm tissue, softer grey-yellow necrotic or myxoid areas, and occasional hemorrhage. The tumor compresses the adjacent normal renal parenchyma, as seen in the image. ## Differential Diagnosis | Feature | Wilms Tumor (Nephroblastoma) | Renal Cell Carcinoma (Pediatric) | Angiomyolipoma | Multicystic Dysplastic Kidney (MCDK) | | :------------------ | :--------------------------------------------------------- | :------------------------------------------------------------- | :--------------------------------------------------------- | :--------------------------------------------------------- | | **Age Group** | Primarily 2-5 years (children) | Adolescents/young adults (rare in young children) | Any age, often adults (associated with Tuberous Sclerosis) | Neonates/infants | | **Gross Appearance**| Large, well-demarcated, tan-white, heterogeneous, often soft | Yellow-orange (lipid-rich), often with hemorrhage/necrosis | Yellow (fat-rich), often multifocal, benign | Multiple non-communicating cysts, absent normal parenchyma | | **Malignancy** | Malignant | Malignant | Benign | Benign developmental anomaly | | **Image Findings** | Matches the image | Not typically this pale/homogenous, usually more yellow/hemorrhagic | Would be distinctly yellow/fatty | Would be cystic, not solid | ## Clinical Relevance **Clinical Pearl:** Wilms tumor often presents as an **abdominal mass** in a young child, sometimes with hypertension, hematuria, or abdominal pain. Early diagnosis and multidisciplinary treatment (surgery, chemotherapy, radiation) lead to excellent outcomes. ## High-Yield for NEET PG **High-Yield:** Wilms tumor is associated with several genetic syndromes, including **WAGR syndrome** (Wilms tumor, Aniridia, Genitourinary anomalies, intellectual disability) due to *WT1* gene deletion, and **Denys-Drash syndrome** (gonadal dysgenesis, nephropathy, Wilms tumor) also involving *WT1* mutations. **Key Point:** The classic triphasic histology of Wilms tumor includes blastemal, stromal, and epithelial components. ## Common Traps **Warning:** Do not confuse the solid, heterogeneous appearance of Wilms tumor with purely cystic lesions like multicystic dysplastic kidney, or with the typically yellow, fatty appearance of angiomyolipoma. ## Reference [cite:Robbins & Cotran Pathologic Basis of Disease, 10th Ed, Ch 24, p. 1069-1070] [cite:Nelson Textbook of Pediatrics, 21st Ed, Ch 518, p. 2727-2730]