Imaging of congenital mesoblastic nephroma with pathological correlation.

BACKGROUND: There are a variety of imaging findings for congenital mesoblastic nephroma (CMN) and two main pathological variants: classic and cellular.

OBJECTIVE: To determine whether imaging findings in children can predict the likely pathological variant.

MATERIALS AND METHODS: We reviewed imaging in children with pathology-proven CMN. Imaging findings correlated with gross and histological appearance.

RESULTS: In 15 boys and 15 girls with CMN, US was performed in 27, CT in 19, and MRI in 7. Cystic components were readily identified on US; central hemorrhage was better differentiated on CT. MRI demonstrated high sensitivity for both. Histology confirmed classic CMN in 13 children, cellular CMN in 14 and "mixed" CMN in 3. Age at presentation was significantly higher in children with the cellular variant. Of 15 solid or predominantly solid tumors and 10 lesions with a hypoechoic ring, 12 and 7, respectively, had pathology consistent with classic CMN. In contrast, five of seven with intratumoral hemorrhage and all with a large cystic/necrotic component had pathology consistent with the cellular variant.

CONCLUSION: The imaging appearance of CMN is often determined by the pathological type of tumor. Findings suggestive of the classic variant include a peripheral hypoechoic ring or large solid component. In comparison, cystic/necrotic change and hemorrhage is much more common in cellular CMN.