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Paediatric Pathology Online

Wilms' tumour (Nephroblastoma)

 Dr Sampurna Roy MD 

                

                                                                                                                      

 

 

Wilms' tumour (Nephroblastoma) is the most common renal neoplasm of childhood.

Visit: Paediatric Pathology Online  ;  Pediatric Renal Tumours

Of all childhood malignancies it has the highest probability of long-term survival with an overall cure rate of approximately 90%.

The random risk of developing Wilms' tumor has been estimated to be 1 in 10,000 births.

At diagnosis, 6% of tumors are bilateral.

Wilms' tumour  usually occurs before 6 years.

Nephroblastoma is rare in young infants when mesoblastic nephroma or rhabdoid tumour are more likely.

Congenital Wilms' tumors have been reported but are extremely rare.

Most tumours weigh between 100 and 1000 gm.

The cut surface of the tumour typically shows lobulated gray/white tissue replacing a large proportion of the kidney.

Focal hemorrhage and necrosis are commonly seen. The tumour may be multifocal.

The primary treatment used to be nephrectomy, followed by chemotherapy.

Examination of the specimen is key to staging.

Careful inking of the specimen capsule prior to fixation and incision is essential to prevent over-diagnosis of capsular invasion.  

The pathologists should routinely attempt to identify the renal vein and examine its lumen for tumour at the time of gross examination.

The cut surface of the tumour typically shows lobulated gray/white tissue replacing a large proportion of the kidney.

Focal hemorrhage and necrosis are commonly seen. The tumour may be multifocal.

The primary treatment is nephrectomy, followed by chemotherapy.

Examination of the specimen is key to staging.

Careful inking of the specimen capsule prior to fixation and incision is essential to prevent over-diagnosis of capsular invasion.  

The pathologists should routinely attempt to identify the renal vein and examine its lumen for tumour at the time of gross examination.

Attention is given to renal capsule, vessels, ureter, pelvis and lymph nodes as in adult specimens.    

To ensure adequate tissue sampling at least one tumour section should be taken for each centimeter diameter of tumour.  

Histological blocks from the kidney tumour interface are particularly informative and may demonstrate precursor lesions. 

The renal sinus should be sampled.

Until recently invasion of the renal sinus (which does not have a capsule) did not upstage an otherwise localised tumour to stage 2. 

This is revised in the light of experience so that infiltration of the renal sinus equates with capsular penetration for staging purposes.

Staging is best determined by a multidisciplinary paediatric oncology team.

Some protocols indicate chemotherapy prior to nephrectomy to shrink the tumour and reduce the chance of spillage.

Needle biopsy used has a significant diagnostic error rate, and has resulted in needle track seeding in occasional cases.

The tiny specimen produced challenges to even the most experienced pathologists and immuno-histochemistry, electron microscopy and occasionally molecular methods are necessary to establish the diagnosis.

 

 

Wilms' tumour consist of blastemal, stromal and epithelial elements, any one of which may be predominant.

The basic microscopic pattern of Wilms' tumour is a biphasic growth composed of islands of metanephric blastema separated by mesenchyme.

The metanephric blastema is a compact arrangement of small oval/polygonal cells with hyperchromatic nuclei and scant cytoplasm.

There may be variable epithelial differentiation usually in the form of tubules showing degrees of lumen-formation.

Glomeruloid structures are infrequently present.

When one component occupies more than 65% of the cross sectional area of tumour,the pattern is subtyped as predominant; example, blastema-epithelial-or stromal-predominant.  

When no single component predominates the tumor is referred to as one of mixed pattern.

The mixed pattern constitutes the largest single group.

In the context of modern chemotherapy the predominant element is not of prognostic significance, although blastemal tumours as a group have a poor outcome because they tend to present a more advanced stage.

So-called rhabdomyomatous Wilms' tumour, which has an extensive immature striated muscle component tends to occur in young children, prolapse into the renal pelvis, and is sometimes bilateral.

The single most important prognostic histological feature is the presence or absence of anaplasia.

Anaplasia is defined as :

(1) the presence of nuclei 3x the diameter of adjacent nuclei of the same tissue type,

(2) which are hyperchromatic, and

(3) atypical mitoses. All three criteria must be met.

Anaplasia may be focal or diffuse. The definition of focal or diffuse anaplasia has recently been revised recognizing that discrete foci of anaplasia confined to the excision specimen but not present in extrarenal sites or residual tumour do not confer adverse prognosis.

Anaplasia is most often found in non-whites, older children and tumours with lymph node metastases.

It is believed to be the morphological manifestation of genetic instability and multiple drug resistance.

Chemotherapy may alter the histology of Wilms’ tumour causing necrosis, "maturation" and fibrosis.

It does not produce anaplasia, so the finding of anaplasia after chemotherapy has the same significance as the untreated tumours.

The diagnosis of Wilms' tumour is usually not problematic in untreated nephrectomy specimens if the differential diagnosis are kept in mind.

Immunohistochemistry is rarely helpful, although epithelial markers may highlight tubular differentiation in blastemal predominant tumours.

Electron microscopy may show a thick basal lamina like fuzz around each cell composed of neural cell adhesion molecule (NCAM). This is unique to Wilms' tumour.

Metastatic sites usually involve regional lymph nodes, lung and liver. Bone is rarely affected.

There are several rarer entities which are related to Wilms' tumour histologically, but carry a more favourable prognosis. Wilms' tumour related lesions

Further reading:

Wilms' tumor: past, present and (possibly) future.

Nephroblastic neoplasms.

Metanephric neoplasms: the hyperdifferentiated, benign end of the Wilms tumor spectrum?

Identical genetic changes in different histologic components of Wilms' tumors.

Nephroblastomas (Wilms' tumors) and special variations of nephroblastomas

New aspects of nephroblastoma (Wilms tumor) and other metanephrogenic neoplasms .

Clinicopathologic features and prognosis for Wilms' tumor patients with metastases at diagnosis.

Anaplastic Wilms' tumor: clinical and pathologic studies.

Wilms' tumor and other renal tumors of childhood: a selective review from the National Wilms' Tumor Study Pathology Center.

Histology and prognosis of nephroblastoma--with special reference to special variants

Histopathology and prognosis of Wilms tumors: results from the First National Wilms' Tumor Study.

 

 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)


 

 

 

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