Renal Mass Approach
A renal mass is sorted first into cystic vs solid and then benign vs malignant — most are incidental, and management runs from surveillance to nephron-sparing surgery.
The big picture
Every renal mass faces two questions: is it cystic or solid, and is it benign or malignant? Cystic lesions are graded by the Bosniak system (higher grade = higher malignancy risk); solid enhancing masses are renal cell carcinoma until proven otherwise.
Solid enhancing mass = RCC until proven otherwise; characterise (Bosniak for cystic), risk-stratify, and spare the nephron whenever oncologically safe.
Mechanism pathway
Tap any step to see why it happens.
Diagnostic algorithm
Each step answers one question. Tap to expand.
Classification & subtypes
Simple cyst (Bosniak I–II)
Thin-walled, non-enhancing fluid lesions.
- Why it matters:
- Benign; no follow-up needed for I–II.
- Management:
- Reassure; IIF gets surveillance.
- Memory hook:
- Thin, no enhancement = benign cyst.
- Board trap:
- Over-investigating a simple cyst.
Complex cyst (Bosniak III–IV)
Thick walls, septa or nodular enhancement.
- Why it matters:
- Rising malignancy risk with grade.
- Management:
- Surgery or surveillance by grade/fitness.
- Memory hook:
- Enhancing septa/nodule = treat.
- Board trap:
- Calling an enhancing complex cyst benign.
Solid enhancing mass
Enhances after contrast.
- Why it matters:
- RCC until proven otherwise.
- Management:
- Surveillance/biopsy/ablation/partial/radical by size and fitness.
- Memory hook:
- Solid + enhances = RCC until proven otherwise.
- Board trap:
- Assuming a solid mass is benign without work-up.
Fat-containing mass
Macroscopic fat on CT (no calcification).
- Why it matters:
- Suggests benign angiomyolipoma.
- Management:
- Surveillance; treat large/bleeding AMLs.
- Memory hook:
- Macroscopic fat = think AML.
- Board trap:
- Fat-poor AML can mimic RCC.
Treatment ladder
Match intensity to malignancy risk and patient fitness while preserving renal function.
Procedure chooser
- Partial nephrectomy (preferred) for localised tumours
- Radical nephrectomy for large/central tumours not amenable to sparing
Follow-up
- Mass size/growth on surveillance imaging
- Renal function
- Recurrence after treatment
- Interval imaging for surveillance; protocol-based post-treatment
- Stable small mass on surveillance, or treated with preserved function
- Growth/progression on surveillance, or recurrence
- Per surveillance protocol; new symptoms
- CKD risk after nephron loss; recurrence; metachronous lesions
Memory hooks
Cystic vs solid, then benign vs malignant.
Enhancement = the key sign.
Solid enhancing = RCC until proven otherwise.
Macroscopic fat = AML.
Spare the nephron.
Board traps
Bosniak III/IV cyst with enhancing components treated as benign.
Small mass in a solitary kidney removed radically.
Fat-poor AML mistaken for, or distinguished from, RCC.
Clinical cases
A healthy 58-year-old has an incidental 3 cm solid, enhancing lower-pole renal mass with a normal contralateral kidney.
What is the working diagnosis and the preferred treatment?