Perinatal/Neonatal Casebook ⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢ Special Imaging Casebook

Thomas E. Herman, MD the lung, heart, bone, and brain.9 The ratio of classic to cellular tu- Marilyn J. Siegel, MD mors is 1:2 among patients with aggressive relapsing CMN and for patients with nonrelapsing tumors. Pathologically, cysts are found in ϳ25%10 of tumors. Cystic CASE PRESENTATION lesions sometimes show a pooling of contrast medium at the time of A 4200-gm infant was born by normal vaginal delivery at term at computed tomography or intravenous urography.11 This is thought to an outside hospital. The newborn was healthy and was routinely be due to excretion into a cyst by functioning nephrons trapped within discharged from the nursery. The child suddenly developed gross the tumor.12,13 hematuria at 15 weeks of life. A renal sonogram (Figure 1) was The cell of origin of mesoblastic nephroma is not known, al- performed that demonstrated a cystic right renal mass and a nor- though the tumor usually contains predominantly myofibroblastic mal left kidney. The child subsequently underwent a right ne- elements.8 There is increasing evidence that CMN and Wilms’ tumor phrectomy. have a common etiology. The prime evidence is the occasional associ- ation of mesoblastic nephroma with both nephrogenic rests and Beck- 14 DENOUEMENT AND DISCUSSION with-Wiedemann syndrome. This has led to the hypothesis that a Congenital Cystic Mesoblastic Nephroma mesoblastic nephroma results from an induction of primitive blast- The pathologic specimen demonstrated a cystic mesoblastic ema at a point when it is not metanephric but only stroma- 2,8,14,15 nephroma. It was composed of typical spindle cells with minimal genic. The malignant clear cell sarcoma is believed to be the 4 pleomorphism and cysts lined by flat columnar epithelium. There most aggressive end of the spectrum of this stromal tumor induction. was neither capsular nor hilar fat invasion. There is a significant difference in age of presentation between Congenital mesoblastic nephroma (CMN) is an uncommon classic CMN and cellular CMN. The average age at presentation for 4 renal tumor of the neonatal period and early childhood, account- classic CMN is 5 days of life; for cellular CMN, it is 5.3 months. In ing for ϳ3% of all pediatric renal tumors.1,2 Although originally fact, patient age is thought to be a relatively important prognostic described by Bolande et al.3 as a benign leiomyoma-like tumor, a factor. Both classic and cellular tumors have an excellent prognosis 16 spectrum of pathology is now appreciated.3,4 under the age of 3 months. However, even age is not a reliable prog- There are two pathologic variants: classic CMN and atypical or nostic feature. Approximately one-third of CMNs that have relapsed cellular CMN.4 Classic CMN is a histologically indolent tumor of have been found in patients of Ͻ3 months of age.9 Patients with CMN monotypical spindle cells with low cellularity and no atypia.5 usually present with a palpable flank mass (95%) and less often with Dilated vessels and entrapped nephrons are sometimes seen at the hematuria (18%),6 hypertension, anemia, jaundice, or vomiting.6,7 periphery of the tumor.4 Perinephric fat infiltration occurs fre- Sonographically classic CMN may appear as a hypoechogenic quently,5,6 but vascular invasion does not. Atypical or cellular CMN tumor with an echogenic rim (the so called ring sign)4 or as a homo- is characterized by high cellularity, frequent mitoses, nuclear geneous or heterogeneous solid mass with no discernible rim. In the atypia, and areas of necrosis.7 However, there is no convincing latter instance, differentiation from Wilms’ tumor is not possible evidence that the prognosis of atypical tumors with dense cellular- sonographically. However, age is an important diagnostic feature, ity, mitoses, and necrosis is significantly different from the classic because 75% of renal tumors in children of Ͻ3 months of age are variety.5 Cystic mesoblastic nephroma is a variant of atypical or CMN. In the case of cystic CMN, the differential diagnosis includes cellular mesoblastic nephroma that was first described in 1981.8 multilocular cystic nephroma, cystic partially differentiated nephro- Rarely CMN exhibits local recurrence and/or distant metasta- blastoma, Wilms’ tumor with cyst formation, cystic renal cell carci- ses develop. Of the 330 cases of CMN in Dr. Becroft’s files,5 7.3% noma, and cystic clear cell sarcoma.17 have had local recurrence or metastases; a total of 1.8% of patients The treatment of patients with CMN of Ͻ3 months of age is have died with persistent disease. The sites of metastases include nephrectomy alone with adequate margins to avoid leaving tumor in the perirenal fat.6 Chemotherapy is indicated for patients with distant Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO. metastases, microscopic residual tumor, or tumor rupture. Recur- Address correspondence and reprint requests to Thomas E. Herman, MD, Mallinckrodt Insti- tute of Radiology, Washington University School of Medicine, 510 South Kingshighway Bou- rences or relapses are usually managed with a combination of surgery 1 levard, St. Louis, MO 63110. and chemotherapy. Patients older than 3 months at the time of diag-

Figure 1. Longitudinal (A), transverse right renal sonograms (B,C), and longitudinal left kidney (D). A multicystic renal mass (arrows) is present involving most of the anterior portion of the right kidney. The left kidney is normal. Sp, spine; L, liver; SL, spleen; RK, right kidney; LK, left kidney.

nosis are more likely to require chemotherapy. Sonography is usually 5. Becroft DMO, Mauger DC, Skeen JE, Ogawa O, Reeve AE. Good prognosis of cel- the examination of choice to follow patients who have had nephrec- lular mesoblastic nephroma with hyperdiploidy and relaxation of imprinting of tomy for CMN. the maternal IGF2 gene. Pediatr Pathol 1995;15:679–88. 6. Howell CG, Othersen HB, Kiviat NE, Norkool P, Beckwith JB, D’Angio GJ. Therapy References and outcome in 51 children with mesoblastic nephroma: a report of the national 1. Wootton SL, Rowen SJ, Griscom NT. Congenital mesoblastic nephroma: pediatric Wilms’ Tumor Study. J Pediatr Surg 1982;17:826–30. case of the day. Radiographics 1991;11:719–21. 7. Carpenter PM, Mascarello JT, Krous HF, Kaplan GW. Congenital mesoblastic 2. Vujanic GM, Delemarre JFV, Moeslichan S. Mesoblastic nephroma metastatic to nephroma: cytogenetic comparison to leiomyoma. Pediatr Pathol 1993;13:435– the lungs and heart: another face of this peculiar lesion. Pediatr Pathol 1993;13: 41. 143–53. 8. Ganick DJ, Gilbert EF, Beckwith JB, Kiviat N. Congenital cystic mesoblastic 3. Bolande RP, Brough AJ, Izant RJ. Congenital mesoblastic nephroma of infancy. nephroma. Hum Pathol 1981;12:1039–43. Pediatrics 1967;40:272–8. 4. Chan HSL, Cheng MY, Mancer K. Congenital mesoblastic nephroma: a clinicora- 9. Schlesinger AE, Rosenfield NS, Castle VP, Jasty R. Congenital mesoblastic diologic study of 17 cases representing the pathologic spectrum of the disease. nephroma metastatic to the brain: report of two cases. Pediatr Pathol 1995;25: J Pediatr 1987;111:64–70. 73–75S.

Journal of Perinatology 2000; 3:198–200 199 Herman and Siegel Congenital Mesoblastic Nephroma

10. Marsden HB, Newton WA. New look at mesoblastic nephroma. J Clin Pathol 1986; 14. Vujanic GM. Congenital cystic mesoblastic nephroma: a rare cystic renal tumour 39:508–13. of childhood. Scand J Urol Nephrol 1992;26:315–7. 11. McAlister WH, Siegel MJ, Askin F, Shackelford GD. Congenital mesoblastic 15. Vujanic GJ, Sandstedt B, Dijoud F, Harms D, Delemarre JFM. Nephrogenic rest nephroma. Radiology 1979;132:356. associated with a mesoblastic nephroma: what does it tell us? Pediatr Pathol 12. Hartman DS, Lesar MSL, Madewell JE, Lichtenstein JE, Davis CJ. Mesoblastic 1995;15:469–75. nephroma: radiologic pathologic correlation of 20 cases. AJR Am J Roentgenol 16. Gaillard D, Bouvier R, Sonsino E. Nucleolar organizer regions in congenital 1981;136:69–74. mesoblastic nephroma. Pediatr Pathol 1992;12:811–21. 13. Kirks DR, Kaufman RA. Function within mesoblastic nephroma: imaging-patho- 17. Agrons GA, Wagner BJ, Davidson AJ, Suarez ES. Multilocular cystic renal tumor in logic correlation. Pediatr Pathol 1989;19:136–9. children: radiologic-pathologic correlation. Radiographics 1995;15:653–69.

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