Congenital Mesoblastic Nephroma: Report of a Case with Review of the Most Significant Literature

Aims And Background: Congenital mesoblastic nephroma (CMN) is a rare pediatric tumor of the kidney with the highest peak of incidence during the first 3 postnatal months. It has previously been confused with Wilms' tumor (which, on the contrary, is rare during the first six months of age and is still considered a histogenetic congener). CMN almost always has a favourable prognosis. Therefore, CMN needs to be correctly diagnosed and differentiated from other pediatric renal neoplasms. Two morphological subtypes are currently distinguished histologically: the classical or leiomyomatous type and the atypical or cellular type. Mixed forms with a combination of the two patterns are also on record. Recurrence and even tumor-related death have been described in the literature and always related to the atypical form or to the mixed form, particularly in patients aged more than 3 months and in those cases in which the surgical removal was not complete. Opinions concerning post-surgical clinical management, especially in regard to adjuvant therapy, are not unanimous.

Methods: A case of CMN, predominantly of the classical histological subtype diagnosed in a baby with a follow-up of 6 years, is herein presented. The tumor was discovered at birth and surgically removed after one month. Since the tumor showed a high mitotic index (one of the characteristics of the cellular subtype) and the perirenal fat was focally involved with the tumor, the possibility of giving adjuvant chemotherapy was considered. Flow cytometric analysis was also performed which showed a diploid DNA content of neoplastic cells.

Results: The tumor was completely removed, surgical margins were free histologically, and no clear-cut histological features of the atypical subtype were noted. Flow cytometrically, it showed the euploid DNA content. Consequently no additional therapy was given. Six years after surgery the patient is developing well and is free of disease. He has regular follow-up examinations.

Conclusions: CMN almost always pursues a benign clinical course if diagnosed under three months of age and if totally surgically excised independent of histological type. Criteria for management of atypical cases are not unanimous in regard to the benefit of additional therapy after surgery.