Atypical congenital mesoblastic nephroma. Report of a case with karyotypic and flow cytometric analysis.

Atypical congenital mesoblastic nephroma is a rare infantile renal tumor that may behave aggressively in older infants. A case of atypical congenital mesoblastic nephroma occurring in an 8-month-old hispanic male was analyzed by routine histopathologic, cytogenetic, and retrospective flow cytometric analysis for DNA ploidy. Light microscopy revealed marked hypercellularity. The karyotype was abnormal, with the following configuration: 45,XY,-1,-3,-9,-9,-15,-17,-21,+del(1)(q21q25),+der(3), t(3;9;15)(q23;p22;q11),+der(9),t(3;9;15) (q23;p22;q11),+der(9),t(9;?) (p?22;?),+r21, + mar. Retrospective DNA ploidy analysis revealed a DNA index of 1.0. The significance of karyotypic changes occurring in mesenchymal renal tumors of this type is currently unknown. Cytogenetic analysis might be of prognostic value in these potentially aggressive tumors.