A 52-year-old woman from Mumbai with a history of recurrent urinary tract infections presents with left flank pain and gross hematuria. Contrast-enhanced CT abdomen shows a large left renal mass (8 cm) with heterogeneous enhancement, central necrosis, and invasion into the renal vein. There is no evidence of distant metastases. What is the most likely diagnosis?

Explanation

## Clinical Presentation A 52-year-old woman with gross hematuria, flank pain, and a large heterogeneous renal mass with central necrosis and renal vein invasion. This constellation of findings is classic for renal cell carcinoma (RCC), specifically the most common subtype: clear cell RCC. ## Imaging Features of Clear Cell RCC | Feature | Clear Cell RCC | Angiomyolipoma | Oncocytoma | Renal Abscess | |---------|---|---|---|---| | **Size** | Often >4 cm | Variable, <4 cm typical | Usually <4 cm | Variable | | **Enhancement** | Heterogeneous, moderate-to-avid | Fat density (–30 to –100 HU) | Homogeneous, avid | Minimal/rim | | **Necrosis** | Common (central) | Rare | Rare | Common (central) | | **Renal vein invasion** | Yes (20–30%) | No | No | No | | **Calcification** | 10–15% | Rare | Rare | Possible | | **Clinical** | Hematuria, flank pain, systemic symptoms | Incidental, asymptomatic | Incidental, asymptomatic | Fever, pyuria, sepsis | **Key Point:** Clear cell RCC accounts for ~70–80% of all RCCs and is the most aggressive subtype. Renal vein invasion is a hallmark feature and indicates advanced local disease (Stage III). ## Pathophysiology & Imaging Basis ```mermaid flowchart TD A[Renal mass on imaging]:::outcome --> B{Fat density?}:::decision B -->|Yes: AML| C[Angiomyolipoma]:::outcome B -->|No| D{Homogeneous enhancement?}:::decision D -->|Yes| E[Oncocytoma or papillary RCC]:::outcome D -->|No| F{Heterogeneous + necrosis?}:::decision F -->|Yes| G[Clear cell RCC]:::outcome F -->|No| H{Fever + pyuria?}:::decision H -->|Yes| I[Renal abscess]:::outcome H -->|No| J[Other RCC subtype]:::outcome G --> K[Assess for vascular invasion]:::action K --> L[Staging: TNM]:::action ``` ## Why Clear Cell RCC? 1. **Large size (8 cm):** RCCs typically present late; angiomyolipomas and oncocytomas are usually incidental and <4 cm. 2. **Heterogeneous enhancement with central necrosis:** Pathognomonic for RCC; reflects areas of tumor necrosis, hemorrhage, and variable perfusion. 3. **Renal vein invasion:** Highly specific for RCC, especially clear cell type; never seen in benign lesions. 4. **Hematuria + systemic symptoms:** Classic RCC triad (hematuria, flank pain, constitutional symptoms). 5. **No fever/sepsis:** Rules out renal abscess. **High-Yield:** The combination of a large, heterogeneous renal mass with central necrosis and renal vein invasion is virtually pathognomonic for clear cell RCC. ## TNM Staging (This Case) - **T3b:** Invasion of renal vein - **N0:** No regional lymph node involvement - **M0:** No distant metastases - **Stage III** (locally advanced) **Clinical Pearl:** Renal vein invasion does not preclude curative surgery; radical nephrectomy with thrombectomy is indicated if the thrombus does not extend above the hepatic vein. [cite:Robbins 10e Ch 20; Harrison 21e Ch 283]