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Prenatal diagnosis of congenital mesoblastic nephroma

Tulin Ozcan, MD
Section Editors
Louise Wilkins-Haug, MD, PhD
Deborah Levine, MD
Deputy Editor
Vanessa A Barss, MD, FACOG


Nearly two thirds of infantile or fetal abdominal masses are of renal origin. Most are benign and related to hydronephrosis and multicystic dysplasia [1]. Congenital renal tumors are rare, comprising 2.5 to 7 percent of all perinatal tumors. This category includes, in decreasing order of frequency, congenital mesoblastic nephroma, Wilms tumor, rhabdoid tumor, clear cell sarcoma, hamartomas (eg, angiomyolipoma), and ossifying tumor of infancy [2].

Congenital mesoblastic nephroma (CMN) arises from renal mesenchyma and is usually benign. It comprises less than 5 percent of all pediatric renal tumors. About 90 percent present in the first year of life, 50 to 75 percent of cases occur in young infants, and almost none occur after the age of three years [3]. In a literature review including 306 CMNs, 16 percent of the cases presented in utero [4]. After two months of age, Wilms tumor is more common than CMN. (See "Prenatal sonographic diagnosis of cystic renal disease" and "Presentation, diagnosis, and staging of Wilms tumor".)


CMN is a low-grade fibroblastic sarcoma of the kidney and renal sinus. Mesoblastic nephroma is presumed to originate from proliferating nephrogenic mesenchyme. It is similar in gross and histologic appearance to a uterine leiomyoma with spindled cells in bundles, but composed of immature renal stromal cells. The tumor lacks renal blastema and neoplastic metanephric elements, thereby differentiating it from Wilms tumor. In addition, it tends to infiltrate the kidney, rather than form the pseudocapsule of classic Wilms tumor.

There are three pathologic variants: classic (24 percent), cellular (66 percent), and mixed (10 percent) types. The classic form is morphologically identical to infantile fibromatosis of the renal sinus with fusiform spindle cells and rare mitoses. The cellular form is identical to infantile fibrosarcoma and is characterized by a highly cellular spindle cell proliferation with minimal intervening collagen/ supporting stroma, and high nuclear to cytoplasm ratios. The mixed type is composed of areas of low and high cellularity (formed by elongated spindle cells resembling fibroblastic cells seen in benign myofibromas) [5].

CMN is almost always unilateral and is rarely malignant [6]. It may extend beyond the renal capsule, but rarely metastasizes to distant organs. Cellular CMN, older age (older than 3 months at diagnosis), and positive surgical margins appear to increase the risk of recurrence and metastasis [5,7].


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Literature review current through: Jul 2017. | This topic last updated: Mar 20, 2017.
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