Definition/General

Introduction:
-Wilms tumor (nephroblastoma) is the most common primary renal malignancy in children
-It constitutes 90% of pediatric renal tumors
-It arises from metanephric blastema
-FNAC shows characteristic triphasic morphology in classic cases.
Origin:
-Originates from persistent metanephric blastema
-The tumor demonstrates triphasic composition
-Contains blastemal, epithelial, and stromal elements
-Represents embryonal renal neoplasm
-May arise from nephrogenic rests.
Classification:
-Classified according to WHO 2016 classification
-Favorable histology (85-90% cases)
-Unfavorable histology (anaplastic changes)
-Blastemal-predominant
-Epithelial-predominant
-Stromal-predominant
-Mixed type (most common).
Epidemiology:
-Peak incidence at 2-5 years of age
-Slight female predominance
-Associated syndromes (WAGR, Beckwith-Wiedemann, Denys-Drash)
-Bilateral tumors in 5-10% cases
-Indian children show similar age distribution
-Generally good prognosis with multimodal therapy.

Clinical Features

Presentation:
-Abdominal mass (most common, 80-90%)
-Painless abdominal swelling
-Abdominal pain (less common)
-Hematuria (10-25%)
-Hypertension (25%)
-Fever (20%)
-Associated congenital anomalies
-Rapid growth of abdominal mass.
Symptoms:
-Progressive abdominal distension
-Decreased appetite
-Nausea and vomiting
-Constipation (mass effect)
-Respiratory symptoms (large tumors)
-Constitutional symptoms (fever, weight loss)
-Hypertension-related symptoms.
Risk Factors:
-Congenital anomalies (genitourinary, hemihypertrophy)
-Genetic syndromes (WAGR, Beckwith-Wiedemann, Denys-Drash)
-Familial Wilms tumor (rare)
-Nephrogenic rests
-WT1 or WT2 gene mutations
-Caucasian ethnicity (higher incidence).

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Gross Description

Appearance:
-Large, well-circumscribed mass replacing most of kidney
-Gray-tan to pink cut surface with areas of necrosis and hemorrhage
-Soft, fleshy consistency
-Cystic areas may be present
-Size typically large at presentation.
Characteristics:
-Variegated appearance reflecting different tissue elements
-Gray-white areas (blastemal component)
-Pink areas (epithelial component)
-Tan areas (stromal component)
-Areas of necrosis and hemorrhage common
-Calcification possible.
Size Location:
-Generally large at presentation (5-20 cm)
-Unilateral in 90-95% cases
-Bilateral in 5-10% cases (worse prognosis)
-May extend beyond renal capsule
-Inferior vena cava extension possible.

Microscopic Description

Immunohistochemistry

Positive Markers:
-WT1 (blastemal and epithelial components)
-PAX8 (epithelial component)
-CD56 (blastemal component)
-Cytokeratins (epithelial component)
-Desmin (stromal component with muscle differentiation)
-MyoD1 (skeletal muscle differentiation).
Negative Markers:
-CD99 (helps exclude Ewing sarcoma)
-Chromogranin (negative)
-Synaptophysin (negative)
-Lymphoid markers (negative)
-Melanoma markers (negative)
-MyoD1 negative in blastemal component.
Diagnostic Utility:
-WT1 positivity supports Wilms tumor diagnosis
-Combination of markers helps identify different components
-CD56 positivity in blastemal component useful
-Cytokeratin pattern highlights epithelial structures
-Essential for differential diagnosis.

Molecular/Genetic

Genetic Mutations:
-WT1 gene mutations (11p13)
-WT2 locus alterations (11p15.5)
-CTNNB1 mutations (beta-catenin pathway)
-TP53 mutations (anaplastic cases)
-MYCN amplification (rare)
-Loss of heterozygosity at 1p and 16q.
Prognostic Significance:
-Favorable histology (90% 5-year survival)
-Anaplastic histology (worse prognosis)
-1p/16q LOH identifies high-risk patients
-Stage remains most important prognostic factor
-Age and tumor size also important.

Differential Diagnosis

Sample Pathology Report

Template Format

Sample Pathology Report

Complete Report: This is an example of how the final pathology report should be structured for this condition.

Clinical Information

[Age] year old [male/female] with [renal mass/abdominal mass]

Specimen Information

FNAC from [renal mass/abdominal mass], performed under [guidance method]

Specimen Adequacy

[Adequate/Inadequate] for cytological interpretation

Cytological Findings

Cellular smears showing [mixed population/predominant component]. [Triphasic/Biphasic/Monophasic] morphology with [blastemal/epithelial/stromal] elements

Morphological Components

[Blastemal component: small round blue cells]. [Epithelial component: tubular/rosette formation]. [Stromal component: spindle cells]

Nuclear Features

[Nuclear size/Nuclear pleomorphism/Mitotic activity/Anaplastic features if present]

Cytological Diagnosis

[Malignant] - Features highly suggestive of Wilms tumor (nephroblastoma)

Differential Diagnosis

Age-appropriate differentials include [other pediatric renal tumors/small round cell tumors]

Recommendations

URGENT histopathological examination recommended. [Immunohistochemistry panel]. Pediatric oncology consultation advised

Note

Final diagnosis and staging require histopathological examination. Immediate clinical correlation recommended for treatment planning