## Why Partial Nephrectomy is right The structure marked **A** — a heterogeneously enhancing solid renal mass with thick irregular wall and measurable contrast enhancement (ΔHU ≥15–20) — is consistent with Bosniak IV classification and renal cell carcinoma. At 6 cm with confined location (T1b, ≤7 cm confined to kidney), partial nephrectomy is the preferred nephron-sparing approach per Harrison 21e Ch 81. This preserves renal function and is the standard of care for T1b lesions in fit patients. The smoking history and imaging findings are classic for RCC, the most common primary renal malignancy (~90% of adult kidney cancers) arising from proximal tubular epithelium. ## Why each distractor is wrong - **Radical nephrectomy with en bloc resection**: Indicated for T3–T4 disease or when partial nephrectomy is not feasible. This 6 cm mass confined to the kidney (T1b) does not require radical nephrectomy as the first-line approach; partial nephrectomy is preferred to preserve nephrons. - **Surveillance imaging at 3 and 6 months**: Appropriate only for Bosniak I–II cysts (benign) or indeterminate lesions. A Bosniak IV solid enhancing mass with thick irregular walls is ~90% malignant and requires surgical intervention, not surveillance. - **Percutaneous biopsy before treatment**: RCC diagnosis is established by imaging characteristics (enhancement ≥15–20 HU, solid morphology, thick irregular wall). Biopsy is not required and delays definitive treatment. Solid enhancing renal masses in adults are RCC until proven otherwise. **High-Yield:** Bosniak IV (solid enhancing mass with thick irregular walls) = ~90% malignant → surgery; T1b (≤7 cm confined) → partial nephrectomy preferred; smoking is a 2× risk factor for RCC. [cite: Harrison 21e Ch 81 — Bladder and Renal Cell Carcinomas]
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