Congenital renal tumour: metanephric adenoma or malignancy?

Abstract

We report a case of renal tumour detected by prenatal ultrasound and resected at 2 months of age. The patient remains disease-free 18 months following surgery. The tumour was tan solid mass measuring 9 cm in greatest dimension, composed solely of tubular and papillary structures lined by small, uniform epithelial cells. There was local invasion into renal parenchyma and a tumour deposit in a hilar lymph node. The tumour was diffusely positive for WT1, pankeratin, CD10 and vimentin, focally positive for CK7, and negative for EMA and TFE3. The favoured diagnosis was metanephric adenoma over renal cell carcinoma, Wilms tumour or nephrogenic rest. Metanephric adenoma is a rare renal neoplasm with most cases occurring at 50–60 years of age. Cases in children have been recorded, although never prenatally. Tumour deposits in a lymph node are unusual, but have been reported. We attempted to confirm the diagnosis by BRAF immunostaining, based on a recent report that 90% of metanephric adenomas are positive. This series, however, did not include pediatric patients. Our case was immunonegative, as were 2/3 additional cases of nephrogenic adenoma. Thus, BRAF immunostaining may not be a reliable marker for pediatric metanephric adenoma and further study is required.