page_title: Metanephric adenoma
section_title: Histopathology
hierarchical_section_title: Metanephric adenoma / Pathology / Histopathology
caption_attribution_description: English: Micrograph of a metanephric adenoma, a rare benign tumour of the kidney. PAS stain. Metanephric adenomas consist of: Small uniform cells, which have a relatively smooth nuclear membrane, fine chromatin, and no apparent nucleolus. Two normal glomeruli can be identified in the non-tumour portion on the left of the image. The most important differential diagnosis is nephroblastoma (Wilms tumour); these typically have frequent mitoses, an irregular nuclear membrane and prominent nucleoli. Related images High mag. High mag. (cropped)
context_page_description: Metanephric adenoma is a rare, benign tumour of the kidney, that can have a microscopic appearance similar to a nephroblastoma, or a papillary renal cell carcinoma.
  It should not be confused with the pathologically unrelated, yet similar sounding, mesonephric adenoma.
context_section_description: Metanephric adenoma is diagnosed histologically. The tumours can be located at upper pole, lower pole and mid-hilar region of the kidney; they are well circumscribed but unencapsulated, tan pink, with possible cystic and hemorrhagic foci. They show a uniform architecture of closely packed acinar or tubular structures of mature and bland appearance with scanty interposed stroma. Cells are small with dark staining nuclei and inconspicuous nucleoli. Blastema is absent whereas calcospherites may be present. Glomeruloid figures are a striking finding, reminiscent of early fetal metenephric tissue. The lumen of the acini may contain otherwise epithelial infoldings or fibrillary material but it is quite often empty. Mitoses are conspicuously absent.
  In the series reported by Jones et al. tumour cells were reactive for Leu7 in 3 cases of 5, to vimentine in 4 of 6, to cytocheratin in 2 of 6, to epithelial membrane antigen in 1 of 6 cases and muscle specific antigen in 1 of 6. 
  Olgac et al. found that intense and diffuse immunoreactivity for alpha-methylacyl-CoA racemase (AMACR) is useful in differentiating renal cell carcinoma from MA but a panel including AMACR, CK7 and CD57 is better in this differential diagnosis.
  Differential diagnosis may be quite difficult indeed as exemplified by the three malignancies initially diagnosed as MA that later metastasized, in the report by Pins et al.
caption: Micrograph of a metanephric adenoma (right of image). Normal kidney is seen on the left. Kidney biopsy. PAS stain.
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