Renal dysplasia of the sacral region: metanephric dysplastic hamartoma of the sacral region.

We believe this to be the third reported case of an unusual congenital sacral tumor-like lesion characterized histologically by the presence of dysplastic and immature renal-like tissue with a predominant glomerular and tubular structure. This lesion appears important in the differential diagnosis of extrarenal nephroblastoma, and should be regarded as a dysplastic overgrowth. An origin from mesonephric or metanephric remnants is suggested.