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Mesoblastic Nephroma

Valerie L Ward, MD
Donald N DiSalvo, MD

February 12, 1997

Presentation

A 23-year-old woman had a normal prenatal ultrasound at 25.3 weeks gestation. She presented at 33.9 weeks with abdominal pain and fetal size greater than dates.

Imaging Findings

US images of fetus at 33.9 weeks
US image of newborn: right kidney area
US image of newborn: left kidney

Ultrasound (US) images of the fetus at 33.9 weeks demonstrate a right retroperitoneal mass (arrow) and moderate polyhydramnios. The mass replaces most of the right kidney (and internal vascularity was clearly demonstarted with color doppler imaging). The left kidney appears to be normal.

US images of the newborn boy (obtained on day of life 1) demonstrate a 6.3 x 6.0 x 5.6 cm solid right renal mass. The mass contains several cystic spaces (arrows) and multiple vessels. The mass compresses, but does not invade, the inferior vena cava. The left kidney appears to be normal.

Differential Diagnosis

Mesoblastic Nephroma
Mesoblastic nephroma (fetal renal hamartoma) is a mesenchymal neoplasm that arises from the metanephric blastema. This neoplasm is the most common renal neoplasm in the fetus and neonate. A renal mass and polyhydramnios are characteristic findings.

Wilms Tumor
Wilms tumor, an epithelial neoplasm, is rare in the fetus and neonate. It most commonly occurs at around 3 years of age and is characterized by a large abdominal mass.

Nephroblastomatosis
Nephroblastomatosis, a precursor to Wilms tumor, is caused by an arrest in normal nephrogenesis. Both kidneys are diffusely enlarged by this persistent immature metanephric tissue. On imaging, nephroblastomatosis appears as multifocal subcapsular nodules in the renal cortex.

Diagnosis

Mesoblastic nephroma of the right kidney

On day of life 3, the newborn underwent a right radical nephrectomy. The tan-yellow nodular mass (5.6 x 5.3 x 5.3 cm) had a characteristic "whorled" appearance, similar to that seen in a uterine leiomyoma.

Discussion

Prenatal ultrasound diagnosis of mesoblastic nephroma is presumptively made when a solid renal mass is identified in a fetus with polyhydramnios. Many theories have been formed as to the etiology of the polyhydramnios in mesoblastic nephroma. One theory states that fetal hypercalcemia may lead to impaired renal concentrating function, and therefore polyuria and polyhydramnios. A second theory proposes that increased renal blood flow to the mass results in fetal polyuria, and hence increased amniotic fluid volume. A third theory suggests that the extrinsic mass effect on the gastrointestinal tract causes polyhydramnios. The precise association between mesoblastic nephroma and polyhydramnios remains uncertain.

Mesoblastic nephroma is most commonly diagnosed in the first three months of life. An abdominal radiograph may show the large abdominal mass or may be normal. An ultrasound examination will show a solid hypoechoic mass. The imaging appearance of mesoblastic nephroma is similar to Wilms tumor. Therefore, surgical excision is performed in all cases and is usually curative.

Pathologically, the cut surface of the nephrectomy specimen shows a yellow-tan tumor with a "whorled" appearance that is similar to a uterine leiomyoma. This tumor grows between nephrons and replaces a majority of the normal renal parenchyma. Most cases of mesoblastic nephroma are clinically benign. However, there are case reports of local recurrence in incompletely resected tumors, and metastases to the brain, lung, heart and bone. In such cases, patients may be treated with chemotherapy and/or radiation.

References

1. Ambrosino MM, Hernanz-Schulman M, Horii SC, Raghavendra BN, Genieser NB. Prenatal diagnosis of nephroblastomatosis in two siblings. J Ultrasound Med 9: 49-51, 1990.

2. Brandt WE, Helms CA. Fundamentals of diagnostic radiology. Baltimore: Williams & Wilkins, 1991.

3. Blickman JG. Pediatric radiology: the requisites. St Louis: Mosby, 1994.

4. Callen PW. Ultrasonography in obstetrics and gynecology. Philadelphia: Saunders, 1994.

5. Dunnick NR, McCallum RW, Sandler CM. Textbook of uroradiology. Baltimore: Williams & Wilkins, 1991.

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7. Fung TY, Fung YMH, Ng PC, Yeung CK, Chang MZA. Polyhydramnios and hypercalcemia associated with congenital mesoblastic nephroma: case report and a new appraisal. Obstet Gynecol 85: 815-817, 1995.

8. Hartman DS, Lesar MSL, Madewell JE, Lichtenstein JE, Davis CJ Jr. Mesoblastic nephroma: radiologic-pathologic correlation of 20 cases. Am J Roentgenol 136: 69-74, 1981.

9. Kirks DR. Practical pediatric imaging. 2nd ed. Boston: Little Brown, 1991.

10. Schlesinger AE, Rosenfield NS, Castle VP, Jasty R. Congenital mesoblastic nephroma metastatic to the brain: a report of 2 cases. Pediatr Radiol 25 Suppl 1: S73-5, 1995.

11. Vujanic GM, Sandstedt B, Dijoud F, Harms D, Delemarre JFM. Nephrogenic rest associated with a mesoblastic nephroma--What does it tell us? Pediatr Pathol & Lab Med 15: 469-475, 1995.

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