Synovial sarcoma of kidney in a child: A rare presentation.

There are no reported cases in the literature of primary renal synovial sarcoma in pediatric patients. The management of renal synovial sarcoma has been extrapolated from the management of soft tissue sarcomas at other sites. We present a 4-year-old female who was suspected to have Wilms' tumor. The patient underwent guided biopsy as she did not respond to neoadjuvant chemotherapy for Wilms' tumor. The biopsy was consistent with primary renal synovial sarcoma. The child was treated with change in her neoadjuvant chemotherapy regimen and surgery. The diagnosis of synovial sarcoma was confirmed by demonstrating the t (X, 18) translocation using polymerase chain reaction.

INTRODUCTION

Primary renal synovial sarcoma is an extremely rare disease with no reports in the pediatric population and few case reports in adults.[123] These tumors can be misdiagnosed as Wilms’ tumor, which is the most common renal malignancy in children. We report a case of primary renal synovial sarcoma in a child that mimicked Wilms’ tumor clinically and radiologically and discuss its management.

CASE REPORT

A 4-year-old female presented to our hospital with abdominal distension of 2 weeks duration. On examination, she had a right lumbar mass that was ballotable, normal blood pressure, and no dysmorphic feature. Computed tomographic (CT) scan of the abdomen showed an 11 × 8 cm mass arising from the upper pole of the right kidney [Figure 1]. The mass had both solid and cystic areas with calcification. There was a thrombus in the right renal vein extending along the inferior vena cava (IVC) till the right atrium. Her serum creatinine, urine routine examination, chest CT scan, and 24-h urine vanillylmandelic acid (VMA) levels were normal. Based on the clinical, radiological, and laboratory parameters a diagnosis of nonmetastatic Wilms’ tumor of the right kidney was made. At our center, we follow the SIOP-93 protocol for treating Wilms’ tumor.[4] The protocol consists of 4 weeks of neoadjuvant chemotherapy with vincristine and actinomycin D followed by nephrectomy of the involved kidney and postoperative adjuvant chemotherapy and/or radiotherapy based on surgical and pathological findings. It is not mandatory to obtain tissue diagnosis prior to treatment in the SIOP-93 protocol if the clinical and radiological features are consistent with Wilms’ tumor; therefore, our patient did not undergo biopsy or fine-needle aspiration cytology (FNAC). She received 4 weeks of neoadjuvant chemotherapy; however, there was no clinical or radiological response to neoadjuvant chemotherapy. She was not considered suitable for surgical intervention due to involvement of the right atrium with tumor thrombus. The patient underwent a CT-guided biopsy of the right renal mass to ascertain the reason for poor response to neoadjuvant chemotherapy. The biopsy showed sheets of spindle-shaped tumor cells with moderate cytoplasm and hyperchromatic nuclei and immunohistochemistry (IHC) showed that the tumor cells were positive for vimentin, CD99, EMA, S100, and Bcl-2 and negative for CD10, desmin, and myogenin. The IHC was consistent with primary renal synovial sarcoma. No chemotherapy-related changes such as necrosis were seen in the pathological specimen. Based on the biopsy report of synovial sarcoma, the patient was treated with ifosfamide 1.8 g/m2 /day for 3 days and adriamycin 30 mg/m2 /day for 2 days; the chemotherapy was repeated every 21 days. After four cycles of chemotherapy, a CT scan of the abdomen showed a partial response with significant shrinkage of the renal mass and resolution of the right atrial thrombus. She underwent right radical nephrectomy with removal of IVC thrombus. The tumor and thrombus were completely excised. The postoperative histopathological examination was consistent with the findings of the preoperative CT-guided biopsy [Figure 2]. Polymerase chain reaction on the operative specimen was positive for SYT-SSX2 translocation consistent with synovial sarcoma. She received two more cycles of adjuvant ifosfamide and adriamycin. The patient relapsed 5 months after completing her treatment with extensive pulmonary and intracranial metastasis and died due to progressive disease.

Figure 1

Computed tomographic (CT) scan of the abdomen at diagnosis showing a large right renal mass

Figure 2

After chemotherapy, the nephrectomy specimen shows residual tumor composed of spindle-shaped tumor cells admixed with groups of epithelioid tumor cells (H&E 100× magnification)

DISCUSSION

Synovial sarcomas are rare in the pediatric age group. They are commonly seen close to large joints. Common non-Wilms’ renal tumors seen in children include clear cell sarcoma, rhabdoid tumor, renal cell carcinoma, mesoblastic nephroma, and multilocular cystic nephroma.[5] Renal sarcomas that have been described in children are desmoplastic small round cell tumor, Ewing's sarcoma, and anaplastic sarcoma.[6] There have been about 50 case reports of primary renal synovial sarcoma in the adult literature with a mean age of diagnosis of 37 years.[1] A majority of the tumors were localized and nonmetastatic. Diagnosis of synovial sarcoma on morphology is difficult, as it can present as poorly differentiated tumor with sheets of rounds cells, or as a biphasic tumor with spindle and epithelial component or a monophasic tumor composed purely of epithelial or spindle component. Patients with poorly differentiated tumor have poor outcomes. There are no specific clinical or radiological features to differentiate renal synovial sarcoma from Wilms’ tumor. Common immunohistochemical markers that are positive in synovial sarcoma include epithelial membrane antigen (EMA) (90%), Bcl-2 (93%), vimentin (80%), CD99 (48%), keratin (50-80%), and S100 (40-63%).[7] However, these markers can also be positive in Ewing's sarcoma and hemangiopericytoma.[7] The gold standard for diagnosing synovial sarcoma remains the demonstration of SS18-SSX fusion gene using polymerase chain reaction to identify the presence of a t (x,18) translocation.[8] We were able to demonstrate the translocation in our patient. Synovial sarcoma can be differentiated from Wilms’ tumor based on morphological features and the absence of WT-1 staining on IHC.[7]

Our case highlights the importance of obtaining tissue diagnosis in all patients with Wilms’ tumor prior to the initiation of neoadjuvant chemotherapy. The rates of wrong diagnosis when patients were started on neoadjuvant chemotherapy without biopsy confirmation were 5% in SIOP 9 trial.[9] A trucut biopsy performed prior to starting neoadjuvant chemotherapy does not upstage the patient and is routinely used in the United Kingdom Wilms’ tumor studies.[10] FNAC of the renal mass will also help in diagnosis of Wilms’ tumor and IHC can be performed on the FNAC specimen to confirm the diagnosis. There are no specific guidelines for the management of synovial sarcomas of the kidney. Surgery and chemotherapy with or without radiotherapy is required for the treatment of synovial sarcoma. Our patient did not receive postoperative radiotherapy as her tumor was completely excised with negative margins and in view of her young age. However, our patient expired within 5 months of completing treatment due to disease relapse, attesting the aggressive nature of primary renal synovial sarcoma. This case is being presented for its rarity and the importance of obtaining tissue diagnosis before starting neoadjuvant chemotherapy in patients with suspected Wilms’ tumor.

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Conflicts of interest

There are no conflicts of interest.