Metanephric adenoma of the kidney: an unusual diagnostic challenge

Abstract

Although metanephric adenoma (MA) is a rare, benign neoplasm of epithelial cells, it is often difficult to distinguish this entity from other malignant neoplasms preoperatively. We report a case of a large renal mass for which preoperative diagnosis was indeterminate, with the differential diagnosis including Wilm's tumor, MA, and papillary renal cell carcinoma (PRCC). Accurate postoperative differentiation of MA from PRCC is critical because adjuvant therapy is considered after surgical resection of PRCC tumors.

Keywords: Wilm’s tumor; differential diagnosis.; metanephric adenoma; papillary renal cell carcinoma.

Figure 1

Magnetic resonance angiography image of the pelvis and abdomen in the axial (A) and coronal (B) planes. Arrows indicate the location of a large mass (7.6×10.6×7.3 cm).

Figure 2

Microphotographs of the renal tumor. The histopathological and immunohistochemical findings are consistent with metanephric adenoma (MA). (A) Retiform and micropapillary architecture of the tumor [hematoxylin-and-eosin stain (H&E); magnification, 40×]. (B) Focal cystic and hyaline change in the tumor (H&E; 40×). (C) Epithelial cells of the tumor showing scant cytoplasm; oval, often grooved nuclei, and a lack of mitotic activity (H&E; 400×). (D) Hyalinized and edematous tumoral stroma with scattered psammoma bodies (concentrically laminated microcalcifications) (H&E; 100×). (E) Diffuse, strong positive cytoplasmic immunostaining of the tumor for CD57 (200×). (F) Diffuse, strong positive nuclear immunostaining of the tumor for WT-1 (200×).