Wilms Tumour Pathology
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Direct answer
A huge, painless, smooth flank mass in a child under five — peak age around three years — is the presentation of Wilms tumour (nephroblastoma), the commonest primary renal malignancy of childhood. Histology is triphasic: primitive small blue blastemal cells, tubular epithelial structures and mesenchymal stroma, occasionally with heterologous striated muscle or cartilage. Genetics anchors the syndromes — WT1 loss with aniridia in WAGR and with pseudohermaphroditism and mesangial sclerosis in Denys-Drash, WT2 (11p15, IGF2) dysregulation in Beckwith-Wiedemann — while anaplasia, marked by abnormal TP53-mediated mitoses, defines the unfavourable histology that resists chemotherapy. Modern multimodal treatment cures the large majority.
What you must remember
- Presentation: abdominal mass, sometimes with haematuria or hypertension (renin); mean age about three years; bilateral in syndromic children — routine ultrasound surveillance screens them.
- Triphasic histology: blastema (densely packed small blue cells), epithelial tubules and glomeruloid bodies, and stromal spindle cells — all three components recapitulating metanephric differentiation.
- Anaplasia: enlarged, hyperchromatic, tripolar or multipolar mitotic figures and nuclear gigantism; predicts chemotherapy resistance and defines unfavourable histology; TP53-mutated.
- WT1 syndromes: WAGR — Wilms, aniridia, genitourinary anomalies, mental retardation (11p13 deletion); Denys-Drash — male pseudohermaphroditism, diffuse mesangial sclerosis, high tumour risk (WT1 point mutations).
- WT2 syndromes: Beckwith-Wiedemann (11p15 imprinting) — hemihypertrophy, macroglossia, omphalocele — with Wilms and hepatoblastoma risk; loss of heterozygosity at 1p and 16q marks higher-risk disease needing intensified treatment.
- Precursor: nephrogenic rests (persistent embryonal renal tissue) in the adjacent kidney.
- Outcome: cure rates exceeding 85% overall with surgery plus chemotherapy (radiotherapy for higher stages); Indian paediatric oncology units report comparable results when treatment is completed.
Wilms or neuroblastoma?
Two children, each with a hard abdominal mass crossing the midline, and the diagnostic fork decides everything. The Wilms child is a well-grown three-year-old with a smooth, firm renal mass that moves with respiration and retains a smooth renal outline; the neuroblastoma child is often unwell, with fever, weight loss and a fixed, irregular mass of adrenal or sympathetic-chain origin that typically pushes the kidney down and out rather than replacing it. Laboratory confirmation splits cleanly: neuroblastoma secretes catecholamines — urinary vanillylmandelic and homovanillic acids — while Wilms hypertension relates to renin. Imaging shows fine, punctate calcification in neuroblastoma versus the solid, heterogenous renal mass of Wilms, which may contain cystic and haemorrhagic areas. Metastasis patterns differ: neuroblastoma seeds marrow and bone (the MIBG scan and marrow aspiration stage it), Wilms spreads to lungs and regional nodes. Histology ends the debate: Homer-Wright rosettes and small blue cells with salt-and-pepper chromatin versus the triphasic nephroblastoma — and the paediatric oncology units that follow SIOP protocols give pre-operative chemotherapy, while many Indian centres perform upfront nephrectomy for resectable disease.
Syndromes and anaplasia
Two viva clusters recur. The gene-syndrome mapping — WT1 with aniridia and genital anomalies, 11p15 with overgrowth — must be instantaneous. And anaplasia is not merely "bad-looking": it is a defined entity of multipolar mitoses and nuclear atypia that predicts resistance to standard chemotherapy, escalates treatment intensity, and accompanies TP53 mutation — the reason the pathologist's mitotic-count question is never idle in a paediatric renal tumour.
Frequently asked questions
What are the three histological components of Wilms tumour?
Blastema (small blue primitive cells), epithelial tubules and glomeruloid structures, and mesenchymal stroma — the triphasic pattern of nephroblastoma.
Which syndrome pairs Wilms tumour with aniridia?
WAGR — Wilms tumour, aniridia, genitourinary anomalies and mental retardation, from an 11p13 deletion encompassing WT1.
What defines anaplasia and why does it matter?
Enlarged hyperchromatic nuclei with multipolar mitotic figures; it marks chemotherapy-resistant, unfavourable histology associated with TP53 mutation and dictates intensified treatment.
How does neuroblastoma differ from Wilms tumour at presentation?
Neuroblastoma arises in the adrenal or sympathetic chain, secretes catecholamines (urinary VMA and HVA), calcifies finely, displaces the kidney and metastasises to marrow; Wilms is an intrarenal mass spreading to lung.
What are nephrogenic rests?
Persistent embryonic renal precursor tissue, perilobar or intralobular in position, from which Wilms tumours arise and which mark the syndromic kidney for surveillance.