The most common tumors that may be misclassified as papillary RCCs are the following: metanephric adenoma, epithelial-predominant nephroblastoma, (33) clear cell RCC with prominent papillary growth pattern, clear cell papillary RCC, and translocation RCC.
Clusters of foamy macrophages are often seen in papillary RCC, metanephric adenoma, and mucinous and tubular spindle cell RCC; and psammoma body calcifications can be seen in type 1 papillary, chromophobe, and translocation RCCs, and metanephric adenoma.
Metanephric adenoma: the utility of immunohistochemical and cytogenetic analyses in differential diagnosis, including solid variant papillary renal cell carcinoma and epithelial-predominant nephroblastoma.
Metanephric Adenoma (MA) is a histologically and clinically unique and rare benign renal epithelial tumour.
Metanephric Adenoma (MA) also designated "Nephrogenic adenoma" or "Embryonal adenoma" is a rare benign renal tumour which is histologically, immunohistochemically and clinically unique, with an indolent clinicobiological behaviour.1,2 It accounts for only about 0.2% of adult renal epithelial neoplasms with only 130 well documented cases reported in world literature.3 Origin of this renal mass from persistent primitive metanephric epithelium of the proximal nephron is postulated and partly substantiated.1,2 Histologically this tumour seems to be related to epithelial Wilms' Tumour and Nephrogenic Rests and in fact these lesions may coexist.4,5
The case was diagnosed and confirmed as metanephric adenoma.
If remnants of this tissue remain within the renal parenchyma in post natal life, they often develop into Wilms' tumour or rarely into metanephric adenoma.6 Thus Wilms' tumour and metanephric adenoma are histogenetically related and MA is considered to be the benign counterpart of Wilms' tumour in adults.4,6,14 Since they arise from the same precursor tissue, metanephric adenoma and Wilms' tumour may sometimes co-exist and adequate histological sampling is essential to differentiate between the two tumours.4,5 Histologically metanephric adenoma is also very similar to the metanephric hamartomatous element of nephroblastomatosis.5
Apart from these lesions, there are many kind of benign lesions (leiomyoma, metanephric adenoma, lipoma etc.) which have to be separated from the malign tumors to choose the right treatment policy, conservatively or surgically, if surgically, ablative, partial or radical nephrectomy.
World Health Organization (WHO) histological classification of benign renal neoplasms Renal cell tumors Metanephric tumors Mesenchymal tumors Oncocytoma Metanephric adenoma Angiomyolipoma Papillary adenoma Metanephric adenofibroma Leiomyoma Metanephric stromal tumor Hemangioma Lymphangioma Reninoma Fibroma Schwannoma Renal cell tumors Mixed epithelial mesenchymal tumors Oncocytoma Cystic nephroma Papillary adenoma Mixed epithelial and stromal tumor
The positivity for cytokeratin 7, cytokeratin 8/18, and vimentin is useful in differentiating papillary RCC from other primary renal neoplasms, including metanephric adenoma, chromophobe RCC, oncocytoma, and urothelial cell carcinoma of the renal pelvis.
The differential diagnosis of this tumor includes metanephric adenoma, adult Wilms tumor, synovial sarcoma, mucinous tubular and spindle cell carcinoma of the kidney, and the oncocytic and clear cell variants of papillary renal cell carcinoma.
Metanephric adenoma, nephrogenic rests, and Wilms' tumor: a histologic and immunophenotypic comparison.