Metanephric Adenoma

Clinical features

  • Benign neoplasm composed of Metanephric tubular –like primitive cells
  • Mean age- 41 years
  • Range: 11 months- 83 years
  • range of age: 50-60 years-old
  • Most frequent in females
  • Clinical symptoms: flank pain, haematuria and polycythaemia
  •  These tumours are part of a spectrum of tumours composed by different proportions of epithelium and mesenchymal/stromal tissue (metanephric adenoma, metanephric adenofibroma or metanephric stromal tumour).
  • The idea that some author’s advocate that this tumour may be related with papillary renal cell neoplasms is controversial (Pins M et al 1999).

 

Fig 12a -  Metanephric adenoma- Monomorphous small blue cell population in a clean background  forming small tubules or rosettes.(H&E), Cells have round or oval nuclei show no atypia and a minimum amount of cytoplasm.
Fig 12b - Metanephric adenoma- Monomorphous small blue cell population in a clean background  forming small tubules or rosettes.(H&E), Cells have round or oval nuclei show no atypia and a minimum amount of cytoplasm.

 

 

  • Monomorphous small blue cell population in a clean background
  • Clusters, tubules papillae or rosettes
  • Numerous regular naked nuclei are usually present.
  • Round or oval nuclei show no atypia and a minimum amount of cytoplasm.
  • The chromatin is dense and regularly distributed and nucleolus is inconspicuous
  •  No necrosis in the background and mitoses are seen.
  •  Psammoma bodies can be seen in the center of tubular structure

 

Immunocytochemistry

  • CD57: Positive-intense
  • WT1: Positive
  • AMACR: positive
  • Pax 8: positive
  • CK7: negative
  • CD56: Negative( some cases of positivity reported)
  • EMA: Negative

 

Genetic studies

  • 2p deletion
  • BRAF mutation- 90%

 

Differential Diagnosis

  • Wilms tumour (epithelial predominant)
    • Patients are generally younger than 6 years-old
    • Extensive sampling might reveal other Wilms tumour components (blastema, mesenchyma)
    • Blastema is CD56 positive and CD57 negative
    • Wilms tubules are CD57 positive and CD56 negative -similar to immunoprofile of MA
    • No BRAF mutation
  • Solid variant of papillary (chromophil) RCC
    • cells are larger and show moderate amounts of cytoplasm
    • Macrophages are frequently present
    •  CK7: Positive, diffuse and intense
    • EMA: Positive, diffuse and intense
    • WT1 : negative
    • AMACR: positive
    •  trisomy 7 and 17 and sex chromosome loss

 

Main Points

  • Most cases represent incidental findings.
  • Some cases, however may course with polycythaemia, abdominal pain or haematuria. S
  • Only recently two cases of metastasized metanephric adenomas were published. 
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