Most renal masses are now found incidentally on cross-sectional imaging. Contrast-enhanced CT (or MRI) characterises the mass, and the central question is whether a solid, enhancing mass is malignant — which, apart from fat-containing AML, imaging cannot reliably answer, so renal mass biopsy is used when the result will change management.
Clinical Presentation
Over 50% of masses are incidental, and many stay asymptomatic until locally advanced. The classic triad (haematuria, flank pain, palpable mass) now appears in <5% and signals advanced disease. Features suggesting advanced disease: a palpable abdominal mass, a non-reducing or right-sided varicocele, bilateral lower-limb oedema (venous involvement), and cervical/supraclavicular lymphadenopathy. Spontaneous perirenal haemorrhage can obscure an underlying RCC — repeat CT a few months later.
Paraneoplastic Syndromes
Present in 10–20% of metastatic RCC (mnemonic NEW-HALF-CAP): Neuropathy, ESR elevated (most common, 56%), Weight loss, Hypertension (renin), Anaemia, LFTs elevated (Stauffer syndrome — non-metastatic hepatic dysfunction), Fever, hyperCalcaemia (PTH-rP or osteolytic; treat with hydration, furosemide, and bisphosphonates), Amyloidosis, and Polycythaemia (EPO). Apart from hypercalcaemia, they resolve only with excision or systemic therapy.
Laboratory Workup
CBC, urinalysis (including proteinuria), and a comprehensive metabolic panel (electrolytes, LFTs, GFR); the CUA adds ALP and corrected calcium for bone dysfunction. GFR and proteinuria assign a CKD stage that influences management. Refer to nephrology for eGFR <45, confirmed proteinuria, diabetic CKD, or an expected post-operative eGFR <30.
Imaging
Any solid mass enhancing >15 HU without fat is RCC until proven otherwise; ccRCC enhances more than papillary or chromophobe. Macroscopic fat (<−20 HU) is diagnostic of AML (5–10% are fat-poor), but calcification with fat is almost always RCC (calcification is virtually never seen in AML).
| Non-contrast HU (homogeneous) | Interpretation |
|---|---|
| <20 | Simple cyst |
| 20–70 | Indeterminate — needs further evaluation |
| >70 | Haemorrhagic / proteinaceous cyst |
On contrast-enhanced CT, a HU rise >20 is enhancing, <10 is non-enhancing, and 10–20 is indeterminate. The differential for a solid mass includes RCC, oncocytoma, AML, urothelial carcinoma, metastasis, abscess, infarct, and pseudotumour; an infiltrative pattern suggests lymphoma, high-grade urothelial carcinoma, collecting-duct or medullary RCC, sarcomatoid change, or XGP. Tumour size is inversely related to malignancy (≈19–25% of masses <4 cm are benign), and nodes ≥2 cm usually harbour malignancy.
- Modalities — contrast-enhanced CT is the modality of choice; MRI (comparable accuracy) is used when iodinated contrast is contraindicated and is best for adjacent-organ invasion and fat detection (T2 fat-suppression). On ultrasound, simple cysts are anechoic with posterior acoustic enhancement, AMLs are echogenic with a speed-propagation artifact, and anything not meeting strict simple-cyst criteria needs CT. PET has no role in routine RCC staging.
- Contrast safety — group II gadolinium agents are safe at any eGFR (nephrogenic systemic fibrosis is rare, mostly with group I); iodinated contrast needs caution at GFR <45 and saline prophylaxis at GFR <30, and metformin is held with renal insufficiency (risk of biguanide lactic acidosis).
- RENAL nephrometry score grades surgical complexity from five features — Radius, Exophytic/endophytic, Nearness to the collecting system, Anterior/posterior, and Location relative to the polar line (range 4–12; lower scores are more amenable to partial nephrectomy).
- Metastatic staging — chest is the commonest visceral site; obtain a CXR (CT chest for pulmonary symptoms, an abnormal CXR, or high-risk features: thrombus, adenopathy, large size, infiltrative appearance, extensive necrosis). Bone scan only for bone pain or raised ALP; brain imaging only for neurological symptoms.
Renal Mass Biopsy
About 20–30% of clinical T1 solid enhancing masses are benign (up to 40% in younger women; mostly oncocytoma or atypical AML). Biopsy is highly reliable for malignancy (diagnostic rate ~92%, sensitivity ~97%, specificity ~94%, histologic concordance 90% but grade concordance only 62%) and is offered when the result will change management (e.g. suspected metastatic, haematologic, inflammatory, or infectious disease) — not for a young, healthy patient unwilling to accept its uncertainty, nor an older/frail patient who will be managed conservatively regardless. Use core biopsy (2–3 cores, 16–18 G) over FNA; avoid biopsy of purely cystic masses (spillage, sampling error). Overall complications are ~8% (renal haematoma ~5%, the rest minor), with no tumour seeding using modern technique.
Genetic Counselling
Refer for renal malignancy at age ≤46, multifocal/bilateral masses, a family history of renal malignancy, features suggesting a familial RCC syndrome, or syndromic histology (e.g. hybrid oncocytic/chromophobe tumours suggest Birt-Hogg-Dubé).
Self-Test
1. What is the differential diagnosis of a solid renal mass on imaging? Malignant — RCC, urothelial carcinoma, sarcoma, lymphoma, metastasis; benign/other — oncocytoma, AML, abscess, infarct, vascular malformation, pseudotumour.
2. What investigations are recommended in suspected RCC? History and physical; labs (CBC, creatinine, LFTs, calcium); imaging (triphasic CT abdomen/pelvis and CXR or CT chest).
3. What are the paraneoplastic syndromes of RCC (NEW-HALF-CAP)? Neuropathy, elevated ESR, weight loss, hypertension, anaemia, elevated LFTs (Stauffer), fever, hypercalcaemia, amyloidosis, and polycythaemia.
4. What findings suggest ipsilateral adrenal involvement? An enlarged or indistinct adrenal gland on imaging, extensive malignant replacement of the kidney, and a palpably abnormal adrenal gland.
5. What are the complications of renal mass biopsy? Renal haematoma, pain, gross haematuria, pneumothorax, and (rarely) haemorrhage requiring transfusion.