The Extrarenal Wilms tumor (EWSRT) is an extremely uncommon but challenging entity. It was first defined by Moyson et al. [7] in 1961. The most common extrarenal sites are retroperitoneal, lumbosacral, pelvic, inguinal, female genital organs, and paratesticular [4]. In the early years, Cryptorchidism is frequently known as a congenital deficiency [8]. It has been described that in the differentiation of structures involved in testicular descent, WT1 plays a direct role while genital abnormalities and cryptorchidism are frequently observed in male patients with germline WT1 mutations [8]. It is well documented that a tumor suppressor gene for Wilms’ tumor is WT1 and accounts for 25% of ERWT cases [3]. So far, no extrarenal testicle Wilms’ tumor followed by the operation of cryptorchidism descent fixation has been reported in the literature [6].
Currently, the exact mechanism of EWSRT which occurs in extrarenal tissue is unknown [9]. It is supposed that the intrarenal and extrarenal Wilms’ tumors do not share the same embryological origin even having the same histology. Extrarenal Wilms’ tumor may ascend from a more primitive mesonephric or pronephric origin and can have diverse positions, proposed by the generally acknowledged hypothesis for the pathogenesis of ERWT. While an embryonic neoplasm that stems from the metanephric blastema is broadly considered to be nephroblastoma [9]. During the embryologic growth period, the urogenital ridge and mesonephrones are in close proximity. Renal embryonic rests, metanephric blastema, or parts of the mesonephric duct might be replaced to the nearby gonad or Wolffian duct, which can continue in postnatal [9]. It is, therefore, expected that the ectopic metanephric blastemal cells in the paratesticular region may increase ERWT. The cases of ERWT found in the inguinal regions along the spermatic cord and testis, uterus, and sacrococcygeal region may be enlightened by the process [9].
EWSRT lacks characteristic clinical manifestations. The clinical presentation of ERWTs rests on the location and stage of the tumor [10]. So, its diagnosis is extremely difficult preoperatively and usually occurs after surgery. In recognizing the characteristics of ERWT, imaging techniques, comprising the ultrasonography and contrast-enhanced computed tomography, may be beneficial. In some cases, additional imaging such as magnetic resonance study may be required [15]. An assured preoperative diagnosis of ERWT is impracticable despite these imaging tests. Currently, in an unknown childhood mass or ERWTs, the character of the intraoperative freezing segment is not reflected as a part of the surgical principle. The pillar of cure in most pediatric firm tumors is complete exclusion when valid. After the surgical resection of the tumor and pathological assessment of the sample, the analysis of ERWT is prepared almost at all times [11].
For pathological diagnosis of ERWT, the following four standards were suggested by Beckwith and Palmer: (1) extrarenal spot of primary neoplasm; (2) nascent blastematous spindle or round cell component; (3) abortive or embryonal tubular or glomeruloid structure; (4) no indication of teratoma or renal carcinoma [3]. In this case, microscopic examination showed the characteristically simultaneous exhibiting triphasic pattern of Wilms tumor (identical blastemal elements with attempted glomeruli and nascent tubules elements) with nearby foci of nephrogenic rests. With proof of normal testicular tissue in the peripheral area of the tumor, the testicular testis was juvenile, constant with the patient’s age, and was almost totally supplanted by neoplastic elements. The analysis of teratoid Wilms tumor, which is a pretty diverse body in the pathogenesis and embryology with germ cell origin, is submitted due to the overabundance of heterotopic teratomatous elements exceeding 50% of the total microscopic field. We examined the whole specimen in multiple cuts to exclude the teratoid elements. In this case, through multiple materials and careful observation under the microscope, no teratoid element, renal carcinoma, anaplastic area, and tumor necrosis was found in the entire specimen.
The relationship and coexistence of ERWT with a horseshoe kidney have been described before in almost 13% of the testified ERWTs [12]. Both kidneys should be assessed specifically with a CT scan to eliminate any intrarenal tumor after pathologic validation of ERWT [3]. While encountering an abdominal mass in a patient with a horseshoe kidney, the examination of ERWT must be acknowledged [3]. In our case, the contrast-enhanced CT-scan indicated that the kidneys had well-kept morphology with no proof of deformity or parenchymal lesions.
Differential diagnosis comprises of major intrarenal Wilms tumor with extrarenal metastasis, malignant teratoma, neuroblastoma, embryonic rhabdomyosarcoma, and embryogenic germ cell-derived tumors.
(1) The diagnosis of extrarenal Wilms tumor first requires the exclusion of the intrarenal Wilms tumor to metastasize outside the kidney, which can be identified by imaging examination of bilateral renal space-occupying lesions. In this case, CT showed regular kidney morphology, and no obvious abnormal density was found in the parenchyma.
(2) Malignant teratoma: Immature teratoma shows mature and immature tissues in various germ layers. The diagnosis is based on the presence of neuroectodermal daisy clusters or primitive neural tubes, and both the mature and immature neural tissues with multiple germ layers mixed distribution. In our case, the three components of primitive germ component, epithelium-like component, and mesodermal component had been found. The presence of teratomatous components was excluded by the extensive grossing of the variegated areas with detailed histological analysis, thereby it falls into the diagnosis of ERWT.
(3) Neuroblastoma: The tumor cells of neuroblastoma are primitive small cells with deep nucleus staining and inconspicuous nucleoli. ERWT is easily confused with neuroblastoma when it is dominated by primitive germ and lacks epithelial components. But Homer-Wright chrysanthemum is common in neuroblastoma. Immunohistochemically, neuroblastoma expresses cgA, Syn, and NSE, but does not express WT-1. In our case, the appearance of renal tubular structures with different degrees of differentiation in tumors, no Homer-Wright chrysanthemum was found. Immunohistochemical staining showed that the tumor cell is positive for WT-1 and negative for cgA, Syn, and NSE. All of these highly supports the diagnosis of ERWT and excludes neuroblastoma.
(4) Embryonic rhabdomyosarcoma: The tumor tissue is mostly primitive stellate or small round cells. Primitive mesenchymal components and rhabdomyoblasts of different stages are mixed in different proportions, but epithelial-like components do not appear. Immunohistochemical, staining showed that the tumor cells express desmin and myoglobin. In our case, the histological and immunohistochemical characteristics support the diagnosis of ERWT and exclude embryonic rhabdomyosarcoma.
(5) Embryogenic germ cell-derived tumors: These tumors are composed of multiple tumor components. Seventy-five percent of yolk sac tumors, seventy percent of embryonal carcinomas, and sixty-two percent of teratomas have a higher serum AFP level. However, in patients with Wilms’ tumors, a boost of such protein is rarely found. In our case, laboratory analysis showed that serum AFP, CEA, β-HCG, and NSE were well within the normal range, which discriminated ERWT from embryogenic germ cell tumors, so it supports the diagnosis of ERWT.
No systematized standards have been explained so far to cure these lesions due to their uncommonness [13]. Surgical removal proves to be the main stride in the treatment of ERWT. It is broadly assumed that for ERWTs staging, National Wilms’ Tumor Study (NWTS) system is likely to be very useful [14]. Despite suitable histopathology, for all ERWT cases, adjuvant chemotherapy is suggested postoperatively. Bearing in mind the NWTS protocols, the chemotherapy regimen is figured out by histology and phase of the tumor. For unresectable tumors and those with gross residue, recurrence, or metastasis, radiotherapy is suggested [3]. In this case, the child was younger and radiotherapy may have a greater impact on the growth and development of the child and the organs of the reproductive system. Therefore, only chemotherapy was preferred with the regime of vinpocetine and dextomycin. At present, two courses of chemotherapy have been completed, and the follow-up has been good so far, and no recurrence of the tumor has been seen.