Case 141 - Discussion

Uploaded: 2007-10-31, Updated: 2007-11-20

  Metanephric Adenoma
CLINICAL FEATURES
 
  • Belongs to metanephric tumors that are derived from the metanephric blastema. Metanephric adenomas, tumors that are composed exclusively of epithelial nephroblastic cells; metanephric stromal tumors, tumors that are composed exclusively of stromal elements; metanephric adenofibromas, tumors that include a composite of both epithelial and stromal elements;

  • Metanephric Adenoma is most commonly type of the metanephric tumor family, and it occurs most commonly in women; the mean age at presentation is 41 years, with a range of 5 to 83 years;

  • 10% patients with metanephric adenomas present with polycythemia.

GROSS FINDINGS
 
  • well circumscribed but unencapsulated;

MICROSCOPIC FINDINGS
 
  • Architectural patterns: tubular, glomeruloid, papillary, small acinar, and calcospherites in an acellular stroma; Occasionally, the epithelial structures coalesce to form more solid sheets. Importantly, blastema is absent

  • Cytologically, tumor cells are small, uniform, oval epithelial cells that appear bland, with smooth nuclear contours, scant pale-staining cytoplasm, dark-staining nuclei, and inconspicuous to absent nucleoli. Mitoses are absent or quite rare.

  • There is considerable histologic overlap between metanephric adenoma, papillary renal cell carcinoma, and differentiated epithelial nephroblastoma. In order to assure a benign outcome, strict criteria are necessary for the diagnosis: absence of a peritumoral fibrous capsule with a direct interface between the lesion and normal kidney; absent nucleoli; absence of vascular invasion; and virtually absent mitoses.

DIFFERENTIAL DIAGNOSES
 
  • Papillary renal cell carcinoma: EMA+, CK7+, more cellular atypia.
IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS
 
  • Positive: CD56, CD57, and WT1;

  • Negative: EMA, CK AE1/AE3, cytokeratin 7.

TREATMENT AND PROGNOSIS
 
  • Benign lesion, complete excision.

REFERENCES
 
  • AFIP, tumor of the kidney, bladder and related urinary structures, series 4;