Incidental Renal Mass in a Patient with Limited Renal Reserve
A 68-year-old man is referred after a CT urogram performed for recurrent haematuria. He has type 2 diabetes and an eGFR of 34 mL/min/1.73 m². The study shows a 3.2 cm solid, enhancing left renal mass (35 HU unenhanced, 78 HU corticomedullary phase, 60 HU nephrographic phase) arising from the interpolar region. There is a 1.1 cm left renal hilar node and no venous thrombus. The right kidney is small and scarred. His haematuria has been intermittent for six months and cystoscopy was normal. He is otherwise asymptomatic and works full-time as a bus driver. The urology team asks whether percutaneous biopsy should be performed before deciding on management.
1. Using the imaging characteristics, classify the mass and explain how the enhancement pattern informs the differential diagnosis.
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The mass is solid and enhances by more than 20 HU between unenhanced and post-contrast phases (35 to 78 HU), which meets the accepted threshold for a genuinely enhancing renal mass rather than a cyst or pseudotumour. The corticomedullary-to-nephrographic washout pattern (78 to 60 HU) is typical of clear cell renal cell carcinoma, which enhances avidly in the corticomedullary phase and washes out. Papillary RCC usually enhances less and more homogeneously, often 10-20 HU above baseline, and chromophobe RCC tends to show moderate, more homogeneous enhancement. A lipid-poor angiomyolipoma can mimic RCC but usually shows prolonged enhancement without washout. The presence of a 1.1 cm hilar node raises concern for nodal metastasis, although reactive nodes occur. The key judgement is that the imaging pattern is sufficiently characteristic of RCC that the diagnosis is probable but not certain, and the node changes the staging and management discussion.
2. Weigh the case for and against percutaneous biopsy in this patient, and state what you would recommend.
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Arguments for biopsy: the mass is small (3.2 cm), the patient has limited renal reserve (eGFR 34), and a benign diagnosis such as oncocytoma or lipid-poor angiomyolipoma would avoid nephron-sparing surgery or ablation in a kidney he cannot afford to lose. Biopsy can also identify histology that might favour active surveillance or ablative therapy over partial nephrectomy, and it can clarify whether the hilar node is metastatic. Arguments against: biopsy has a non-diagnostic rate of roughly 10-20% and a small risk of bleeding and needle-tract seeding, and a negative result does not exclude RCC because of sampling error. The node is small and may be reactive, so a negative nodal sample would not be definitive. Given the solid enhancing mass with washout, the pre-test probability of RCC is high, and the patient is symptomatic with haematuria. My recommendation is to offer biopsy because the potential to avoid nephron-sparing intervention in a patient with an eGFR of 34 is clinically meaningful, but to counsel that a non-diagnostic result would lead to treatment as presumed RCC. I would also discuss partial nephrectomy versus ablation versus surveillance in a multidisciplinary meeting, and note that the haematuria requires explanation independent of the mass.
3. If the mass were instead 1.8 cm and the patient were 82 years old with a life expectancy of 8 years, how would your approach change?
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Small renal masses under 2 cm have a substantial benign rate (roughly 20-30% in surgical series) and a low rate of metastatic progression, so the balance shifts toward conservative management. In an 82-year-old with an 8-year life expectancy, active surveillance with serial imaging at 3-6 months and then annually is reasonable, with delayed intervention reserved for growth beyond about 3-4 cm or clinical change. Biopsy becomes more attractive because it can confirm benign histology and allow discharge from surveillance, and it can identify aggressive histology that would justify treatment despite age. Ablation is preferred over partial nephrectomy if intervention is needed, given the lower procedural burden. The decision should be shared, incorporating the patient's values about intervention and follow-up burden, and the competing risk of non-cancer death should be explicit.