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;

 后肾腺瘤