Wilms' tumor

* We report a case of a teratoid Wilms tumor arising within a supernumerary ectopic ureteropelvic structure in a 7year-old boy. The tumor was near the right kidney but was completely separate from it. On the contralateral side, the child had a duplication of the ureteral system. Pathologic examination revealed the mass to be completely enveloped by a fibromuscular sac lined by urothelium. The tumor had a botryoid, polypoid architecture and, in addition to areas of classic Wilms tumor, had extensive squamous, mucinous, and columnar elements. Teratoid Wilms tumors are rare and, to the best of our knowledge, have not previously been described as arising either in anomalous urinary structures or at 7 years of age. (Arch Pathol Lab Med. 1998;122:925-928)

This report describes a case of teratoid Wilms tumor arising as a botryoid mass within a fibromuscular sac believed to be an ectopic supranumerary ureteropelviceal structure. A review of the existing literature on teratoid and extrarenal Wilms tumor has led us to believe that this is a unique case that deserves documentation.

REPORT OF A CASE

A 7-year-old boy presented with a 1-week history of diffuse abdominal pain. Physical examination revealed an abdominal mass on the right side and extending to the midline. Abdominal ultrasound revealed that it was apparently located near the right kidney. Computed tomography (Figure 1 ) demonstrated the mass to be adjacent to the right kidney but distinct from the renal parenchyma. An intravenous pyelogram demonstrated hydronephrosis on the right side, compatible with extrinsic obstruction, and a double ureter on the left side (Figure 2). The child was otherwise in good health, with no significant past medical history other than that of a bilateral inguinal hernia repair at 2 years of age. Family history was remarkable for congenital hydronephrosis of unknown etiology in a male sibling. Routine laboratory investigation disclosed no abnormality. The patient underwent an exploratory laparotomy and removal of an 8 x 4-cm freely mobile, retroperitoneal circumscribed mass with no attachment to the kidney. There did appear to be a fibrous pedicle between the mass and the inferior vena cava. The postoperative course was uneventful. The child received vincristine and dactinomycin for 18 weeks, in accordance with the National Wilms Tumor Study5 protocol for stage I tumors. After 18 months of follow-up, no clinical signs of recurrence or metastases have appeared.

PATHOLOGIC FEATURES

Gross Pathology

The mass was spherical, with a diameter of 5 cm, and weighed 111 grams. It was completely enveloped by a smooth, glistening pink capsule. Upon sectioning, approximately 50 mL of turbid greenish-brown fluid with glistening, fine particulate matter was released. Floating nearly freely, with minimal attachment to the wall, was a 5-cm-diameter lobulated, polypoid, and slimy tan-yellow mass with focal areas of necrosis (Figure 3).

After sectioning, the specimen was fixed overnight in 10% buffered formalin. Paraffin-embedded tissue sections were stained with hematoxylin-phloxine-saffron and Alcian blue at pH 2.5.

Microscopic Pathology

The low-power microscopic appearance of the bulk of the tumor resembled a botryoid rhabdomyosarcoma, with a polypoid architecture and a hypocellular, myxoid stroma (Figure 4). No cambium layer was present. The epithelium covering these polypoid projections was of variable composition, made of squamous, columnar, and mucinous elements (Figure 5). The mucinous epithelium was rich in goblet cells and had a tendency to invaginate into the stroma (Figure 6). Staining with Alcian blue at pH 2.5 revealed an acidic intestinal-type mucin. Deep in the stroma were numerous tubular structures, also lined by squamous, cuboidal, and mucinous epithelium, but there was no convincing organogenesis. In many foci, the tumor had a classical triphasic pattern of Wilms tumor, with blastema, stroma, and primitive tubules (Figure 7). There was no evidence of anaplasia. Completely enveloping the tumor was a fibromuscular structure that was partially lined by a hobnail urothelium, most compatible with a ureteropelvic structure. No renal cortical or medullary tissue was seen.

COMMENT

The classic Wilms tumor has a triphasic histologic pattern, with blastemal, stromal, and epithelial components. Heterotopic mesodermal elements are commonly seen but usually involve a minor part of the neoplasm. Tumors with a predominance of heterotopic tissues have been termed teratoid Wilms tumors, and the diagnosis of renal teratoma has been reserved for those of unequivocal renal origin with convincing heterotopic organogenesis.1

As measured against the criteria mentioned above, the tumor we report best qualifies for the diagnosis of teratoid Wilms tumor and not renal or extrarenal teratoma. When reviewing the literature, it becomes apparent that renal teratomas as defined by these criteria are extremely rare. The rarity of renal teratomas is underscored by the lack of a single unequivocal case among the more than 2600 renal tumors accessioned in the National Wilms' Tumor Study Registry as of 1983.1

The term teratoid was first applied in 1984 by Variend et al2 to describe a Wilms tumor that was largely composed of stratified squamous and mucus-secreting columnar epithelium as well as diverse other tissues of mesenchymal derivation. This terminology was subsequently adopted by others who defined teratoid Wilms tumor as a Wilms tumor with a clear predominance of teratoid elements, comprising more than 50% of the tumor.3 It is uncommon, with just 10 cases documented in the literature.2 However, this may be an underestimation of the incidence, as the terminology is still recent.4 Supporting this contention is the review of Fernandes et al,3 in which 3 cases of teratoid Wilms tumor were found among 290 patients with Wilms tumor, between 1964 and 1987.

Some of the reported cases of teratoid Wilms tumor have contained a variety of elements, such as adipose tissue, smooth and skeletal muscle, cartilage, squamous epithelial cysts, neuroglial tissue, and mucinous epithelium. As required by the definition, all had areas of classic Wilms tumor, and none showed convincing evidence that the heterotopic elements were organizing into nonrenal organoid structures. To date, in the 10 reported cases that fulfilled those criteria, 2 were associated with nephroblastomatosis and were unilateral, 3 were associated with nephroblastomatosis and were bilateral, 2 were bilateral but not associated with nephroblastomatosis, and 3 were unilateral and not associated with nephroblastomatosis. In the bilateral cases, the contralateral kidney displayed either teratoid or classic Wilms tumor. In all cases, the patient was 3 years of age or younger. In 3 cases, there was either invasion of the renal pelvis or ureteral obstruction. There were 2 deaths, 1 from postoperative complications and 1 from metastatic disease associated with anaplasia.

The pathogenesis of teratoid Wilms tumor is uncertain. It is unlikely that it is derived from a renal teratoma, given the rarity of renal teratomas and the absence of organogenesis in teratoid Wilms tumors. An alternative explanation, which we favor, is that teratoid Wilms tumors arise from extensive metaplasia of metanephric blastema. In fact, tissues that cannot develop through metaplasia of mesodermal tissues are not seen in teratoid Wilms tumors, in contrast to true teratomas (ie, hair, teeth, intestinal walls with muscularis and ganglion cells, choroid plexus, pancreas, thyroid).

Both the young age at usual onset of the reported teratoid Wilms tumors and their high incidence of bilaterality would be in keeping with a germ cell mutation, as supported by the finding of nephroblastomatosis in half of the reported cases. It has been suggested that these tumors arise from intralobar nephroblastomatosis, which is often associated with heterologous elements and is an early defect in nephrogenesis.9 However, in this patient, a putative simple germ cell mutation seems to stand in contradiction with his older age of 7 years.

The botryoid growth pattern, as in this case, is often displayed by those tumors with a substantial component of heterologous (metaplastic) elements"10 and is a distinctive feature of Wilms tumors arising in a hollow cavity and in the ureteropelvic system in particular.111 This suggests to us that the sac in which the tumor developed was most likely an ectopic ureteropelvic system. Its gross appearance and histology are in keeping with this interpretation, and the fact that the collecting system on the contralateral side was malformed suggests that the malformation might have been bilateral. Thus, whether this tumor should be regarded as ectopic renal or extrarenal hinges upon one's interpretation of the origin of the enveloping sac.

More than 50 cases of extrarenal Wilms tumors have been described.12-20 These tumors are uncommon and account for less than 1% of Wilms tumors.17 Their histogenesis is not completely understood. Although teratomas containing areas of nephroblastomatosis have been described,21-24 the majority of extrarenal Wilms tumors are devoid of teratomatous elements. A more likely origin for most extrarenal Wilms tumors would be misplaced metanephric blastema, as seen in the lumbosacral region25 and the colonic wall.26

We feel this case to be unique, for more than one reason. Although he meets the criteria for a teratoid Wilms tumor, at 7 years of age, this patient was older than any of the previously described patients with this tumor and even clearly above the mean age for Wilms tumor in general. Also unique is that this teratoid Wilms tumor arose from what seems to be a urogenital malformation, an ectopic ureteropelvic structure not connected to the ipsilateral kidney. The only "fibrous" connection noted during surgery was to the inferior vena cava, and it turned out to be vascular.

References

1. Beckwith JB. Wilms' tumor and other renal tumors of childhood: a selective review from the National Wilms' Tumor Study Pathology Center. Hum Pathol. 1983;14:481-492.

2. Variend S, Spicer RD, Mackinnon A. Teratoid Wilms' tumor. Cancer. 1984; 53:193fF1942.

3. Fernandes ET, Parham DM, Ribiero RC, Douglass EC, Kumar APM, Williams, J. TeratoidWilms' tumor: the St Jude experience. J Pediatr Surg. 1988;23:11311134.

4. Ashworth MT, Pizer BL, Spicer RD, Berry PJ. A teratoid Wilms' tumor with raised serum alpha-fetoprotein level. Pediatr Pathol Lab Med. 1996;16:853-859.

5. Kotiloglu E, Kale G, Sevinir B, Hicsdnmez A, Ackoren Z. Teratoid Wilms' tumor: a unilateral case. Tumori. 1994;80:61-63. 6. Magee JP, Ansari S, McFadden DE, Dimmick J. Teratoid Wilms' tumor: a report of two cases. Histopathology. 1992;20:427-431.

7. Vujanic GM. Teratoid Wilms' tumor: report of a unilateral case. Pediatr Pathol.1991;11:303-309.

8. Williams MA, Schropp KP, Noe HN. Fat containing renal mass in childhood: a case report of teratoid Wilms' tumor. J Urol. 1994;151:1662-1653.

9. Mierau GW, Beckwith JB, Weeks DA. Ultrastructure and histogenesis of the renal tumors of childhood: an overview. Ultrastruct Pathol. 1987;11:313-333. 10. Gonzalez-Crussi F, Hsueh W, Ugarte N. Rhabdomyogenesis in renal neoplasia of childhood. Am Surg Pathol. 1981;5:525-532.

11. Weinberg AG, Currarino G, Hurt GE. Botryoid Wilms' tumor of the renal pelvis. Arch Pathol Lab Med.1984;108:147-148.

12. Akhtar M, Kott E, Brooks B. Extrarenal Wilms' tumor: report of a case and review of the literature. Cancer. 1977;40:3087-3091.

13. Andrews PE, Kelalis PP, Haase GM. Extrarenal Wilms' tumor: results of the National Wilms' Tumor Study. J Pediatr Surg. 1992;27:1181-1184. 14. Aterman K. Extrarenal nephroblastomas. J Cancer Res Clin Oncol. 1989; 115:409-417.

15. Broecker BH, Caldamone AA, McWilliams NB, Maurer H, Salzberg A. Primary extrarenal Wilms' tumor in children. J Pediatr Surg.1989;24:1283-1288.

16. Coppes MJ, Wilson PCG, Weitzman S. Extrarenal Wilms' tumor: staging, treatment, and prognosis. I Clin Oncol.1991 ;9:167-174. 17. Fernandes ET, Kumar M, Douglass EC, Wilimas J, Parham DM, Rao BN. Extrarenal Wilms' tumor. J Pediatr Surg. 1989;24:483485.

18. Koretz MJ, Wang S, Klein FA, Lawrence W. Extrarenal adult Wilms' tumor. Cancer. 1987;60:2484-2488.

19. Rasheed K, O'Meara A, Kelleher J, Breatnach F, Fitzgerald RJ. Extrarenal Wilms' tumor. Eur J Pediatr Surg. 1993;3:121-123.

20. Todd DW, Roskos R, Baldwin 1. Extrarenal Wilms' tumor. Minn Med.1984; 67:635-638.

21. Kim YW, Park Y-K, Oh SM, Yang MH. Retroperitoneal teratoma with predominance of nephroblastic elements. I Korean Med Sci. 1990;5:237-242.

22. Park HR, Park CY, Choi NK, Park YE. A case of retroperitoneal teratoma with nephroblastoma. J Korean Med Sci. 1991;6:95-102. 23. Tebbi K, Ragab AH, Ternberg JL, Vietti TJ. An extrarenal Wilms' tumor arising from a sacrococcygeal teratoma. Clin Pediatr.1974;13:1019-1021.

24. Ward SP, Dehner LP. Sacrococcygeal teratoma with nephroblastoma (Wilms' tumor): a variant of extragonadal teratoma in childhood. Cancer. 1974; 33:1355-1363.

25. Posalaky Z, Drake RM, Mawk JR, et al. Ectopic immature renal tissue over the dorsum of lumbar and sacral area in two infants. Pediatrics. 1982;69:336339.

26. Sun CJ, Raffel LJ, Wright LL, Mergner WJ. Immature renal tissue in colonic wall of patient with caudal regression syndrome. Arch Pathol Lab Med. 1986; 110:653-655.

Accepted for publication May 22, 1998.

From the Departments of Pathology (Drs Pawel and de Chadarevian), Radiology (Dr Smergel), and Surgery (Dr Weintraub), St Christopher's Hospital for Children, and Allegheny University of the Health Sciences, MCPOHahnemann School of Medicine, Philadelphia, Pa.

Reprints: Bruce R. Pawel, MD, Department of Pathology, St Christopher's Hospital for Children, Erie Avenue at Front Street, Philadelphia, PA 19134-1095.

Copyright College of American Pathologists Oct 1998
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