Wilms tumour

Epidemiology & context

• Peak: early childhood; can be bilateral/synchronous or metachronous.
• Associations: nephrogenic rests (nephroblastomatosis), WAGR, Beckwith–Wiedemann, Denys–Drash, others.

Clinical clues

• Painless abdominal mass, abdominal pain, haematuria, anaemia; possible renin-mediated hypertension.
• Do NOT palpate vigorously (rupture risk).

Imaging

Ultrasound

• Large, well-defined renal mass; renal parenchyma forming claw sign.
• Heterogeneous echotexture with necrosis/haemorrhage; distortion of collecting system.
• Doppler: assess renal vein/IVC for bland vs tumour thrombus; look for contralateral nephrogenic rests.

CT

• Heterogeneous soft-tissue mass arising from kidney; calcification uncommon (cf. neuroblastoma).
• Enhances less than normal cortex; central low-attenuation necrosis; haemorrhage.
• Typically does not cross midline as aggressively as neuroblastoma; mass effect rather than infiltrative encasement.
• Displacement of aorta/IVC without frank encasement; lymph nodes in renal hilum/para-aortic.
• Chest CT: lung metastases (micronodules). ⚠️ Management of CT-only micromets differs between COG vs SIOP—follow local protocol.

MRI

• T1 low–intermediate; T2 intermediate–high; patchy non-enhancing necrosis/haemorrhage.
• DWI: shows restrict diffusion.
• Best for venous extension mapping (renal vein → IVC → right atrium) and contralateral kidney survey.

Venous extension

• Tumour thrombus in renal vein/IVC; can reach right atrium.
• On imaging: continuity with mass, enhancement, restricted diffusion; expand the vein lumen (vs bland thrombus).
• Level of thrombus (infrahepatic/retrohepatic/suprahepatic/atrial) should be reported for surgical planning.

Spread & complications

• Lungs > liver > nodes; rare bone/brain.
• Rupture (pre/intra-op) → upstaging; peritoneal seeding.
• Bilateral disease or multifocality suggests background nephrogenic rests.

Staging (practical rad view/exam style)

Wilms staging is surgical–pathologic based. Different systems (NWTS/COG vs SIOP) exist, but the 1–5 numbering is the same idea.

• I: confined to kidney, completely resected (renal capsule intact, no spill).
• II: extends beyond kidney (e.g., perinephric fat, renal sinus, renal vein) but completely resected (no gross spillage or +ve margins).
• III: residual tumour confined to abdomen (unresected metastatic nodes, spillage/rupture, +ve margins, Biopsy before nephrectomy in COG, tumour thrombus in IVC/atrial tumour thrombus not completely removed or removed separately).
• IV: haematogenous metastases (lungs are most common; liver next; bone/brain rare).
• V: bilateral renal tumours at presentation.

Don’t get baited by tumour size. Staging is spread + surgical factors, not cm cut-offs.

Differential diagnosis

• Neuroblastoma:
  • Calcifications common, encases vessels, may cross midline.
  • Lacks renal claw sign (not arising from kidney).
  • ± Elevated catecholamine (VMA/HVA)
• Clear cell sarcoma of kidney:
  • Renal mass with bone mets tendency (pathologic dx).
  • Imaging often mimics Wilms; suspect if bone mets or older age.
• Malignant rhabdoid tumour:
  • Infants, aggressive; often calcifies; brain lesions (ATRT).
  • loss of INI1 (SMARCB1) on pathology (buzzword).
• Congenital mesoblastic nephroma:
  • Typical in neonates / <3 months
  • Solid, infiltrative; hypervascular ‘spindle cell’ tumour.
• Multilocular cystic renal tumour / Cystic partially differentiated nephroblastoma: predominantly cystic; thick septa.
• Renal cell carcinoma (older child/adolescent): consider if atypical age or calcified solid mass.

Pearls vs neuroblastoma

• Origin: Wilms = renal; neuroblastoma = adrenal/para-spinal.
• Vessels: Wilms displaces; neuroblastoma encases.
• Calcification: rare in Wilms; common in neuroblastoma.
• Thrombus: venous tumour thrombus favours Wilms.
• Claw sign: present in Wilms; absent in neuroblastoma.

Management notes (radiology-relevant)

• NWTS/COG: for unilateral, resectable Wilms → primary nephrectomy + nodal sampling; biopsy uncommon as it upstages to III.
• SIOP: image-based diagnosis → neoadjuvant chemotherapy → delayed nephrectomy; biopsy generally avoided unless atypical.
• Anticipate need for cardiothoracic input if IVC/right atrial thrombus.

Follow-up & surveillance

• Post-therapy: assess residual mass, new lesions in contralateral kidney, venous patency, treatment-related lung/liver changes.
• Long-term: monitor for metachronous contralateral tumour in patients with nephrogenic rests/syndromic risk.