Congenital mesoblastic nephroma: Report of a case with review of the most significant literature

Aims and background: Congenital mesoblastic nephroma (CMN) is a rare pediat ric tumor of the kidney with the highest peak of incidence during the first 3 postnatal months. It has previously been confused with Wilms' tumor (whi ch, on the contrary, is rare during the first six months of age and is stil l considered a histogenetic congener). CMN almost always has a favourable p rognosis. Therefore, CMN needs to be correctly diagnosed and differentiated from other pediatric renal neoplasms. Two morphological subtypes are curre ntly distinguished histologically: the classical or leiomyomatous type and the atypical or cellular type. Mixed forms with a combination of the two pa tterns are also on record. Recurrence and even tumor-related death have bee n 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 th ose 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 t umor, the possibility of giving adjuvant chemotherapy was considered. Flow cytometric analysis was also performed which showed a diploid DNA content o f neoplastic cells. Results: The tumor was completely removed, surgical margins were free histo logically, and no clear-cut histological features of the atypical subtype w ere noted. Flow cytometrically, it showed the euploid DNA content. Conseque ntly no additional therapy was given. Six years after surgery the patient i s developing well and is free of disease. He has regular follow-up examinat ions. Conclusions: CMN almost always pursues a benign clinical course if di agnosed under three months of age and if totally surgically excised indepen dent of histological type. Criteria for management of atypical cases are no t unanimous in regard to the benefit of additional therapy after surgery.