Indian Journal of Urology
: 2013  |  Volume : 29  |  Issue : 1  |  Page : 53--55

Metanephric stromal tumour: A rare pediatric benign stromal specific renal neoplasm

Seema D Khutti1, Ramani P Kumar1, Karl Sampath2,  
1 Department of General Pathology, Christian Medical College and Hospital, Vellore, Tamilnadu, India
2 Department of Pediatric Surgery, Christian Medical College and Hospital, Vellore, Tamilnadu, India

Correspondence Address:
Seema D Khutti
Department of General Pathology, 84-10 Main Street, Apartment - 457, Briarwood, New York - 11435, United States America


A case of incidentally detected Metanephric Stromal Tumour (MST) is reported here. This is a rare, recently recognized pediatric benign stromal specific renal neoplasm. A review of the English literature revealed only five cases after its original description by Argani et al. Recognition of this entity can spare a child from potentially toxic adjuvant chemotherapy that might be used to treat malignant lesions which are part of the differential diagnosis, particularly clear cell sarcoma of kidney (CCSK).

How to cite this article:
Khutti SD, Kumar RP, Sampath K. Metanephric stromal tumour: A rare pediatric benign stromal specific renal neoplasm.Indian J Urol 2013;29:53-55

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Khutti SD, Kumar RP, Sampath K. Metanephric stromal tumour: A rare pediatric benign stromal specific renal neoplasm. Indian J Urol [serial online] 2013 [cited 2020 Aug 14 ];29:53-55
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Metanephric Stromal Tumour (MST), first described in 2000 by Argani et al., [1] is a rare, purely stromal specific renal neoplasm that mainly affects children. Its characteristic microscopic appearance and immunohistochemical profile helps to differentiate it from congenital mesoblastic nephroma (CMN) and clear cell clear cell sarcoma of kidney (CCSK). Since then, there have been only five case reports of this tumour in the English literature. Its recognition is essential as it spares the patient from unnecessary potentially toxic adjuvant chemotherapy. A case of paediatric metanephric stromal tumour is described and the clinical presentation, radiological and pathological findings, differential diagnoses and biological behaviour are discussed.

 Case Report

A three year old boy presented with a complaint of dribbling of urine. He had one episode of hematuria at two years of age but no other complaints such as abdominal pain, fever, loss of appetite or weight loss. On systemic examination, there were no palpable masses or any other abnormalities. As part of the initial work up, an ultrasonography of abdomen was performed, this showed a partly exophytic hypo-echoic mass arising from the interpolar region, measuring 4.7 × 4.8 × 5.3 cm. Vascularity was noted within the mass, suggestive of Wilm's tumour. Ultrasound guided biopsy of the renal mass was performed, which on microscopic examination showed a tumour composed of sheets of spindle shaped cells with oval to elongated nuclei and moderate amounts of cytoplasm. There was no obvious atypia or any other feature of malignancy. Occasional tubules were noted, lined by cuboidal cells. The biopsy was reported as a spindle cell lesion with occasional tubular structures. The cells were negative for WT-1 and S-100 on immunohistochemistry. Based on the biopsy report and the radiological findings, the patient underwent nephroureterectomy. The operation was uneventful and the patient recovered appropriately.

A kidney measuring nine cm in maximum dimension was received in the laboratory. The external surface was smooth. Sectioning revealed a firm white tumour, 7.5 × 5.5 × 4.5 cm replacing most of the kidney. There were a few small cystic areas containing serous fluid. The neoplasm appeared to abut the pelvis but there was no infiltration into pelvic or perirenal fat [Figure 1]. Microscopically the tumour had a slightly nodular architecture due to varying cellularity and was composed of spindle cells with thin tapered bland nuclei an indistinct cytoplasm [Figure 2]. Focally, a concentric arrangement around entrapped tubules and vessels, imparting 'the onion skin' morphology, was noted [Figure 3]. A few entrapped glomeruli were also present. The tumour was well demarcated from the adjacent kidney, but without a definite capsule [Figure 4]. Some blood vessels showed hypercellularity around the endothelium with thickened walls but there were no features of dysplasia [Figure 5]. Mitotic activity and necrosis were absent. There was no evidence of capsular or vascular invasion, heterologous differentiation or neoplastic epithelium. There were no nephrogenic rests either. On immunohistochemistry, the cells were positive for Vimentin, focally positive for CD-34 [Figure 6] and negative for WT-1, Desmin and Smooth muscle actin. The entrapped tubules showed positivity for Cytokeratin. These findings were consistent with MST. Patient's initial complaint of 'dribbling of urine' subsided after undergoing nephroureterectomy. Patient had come for follow-up after six months of operation. Ultra-sound done during this visit showed no local recurrence.{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}


The origin of MST is not entirely clear, but it is thought to be related to Wilm's Tumour, unlike other renal stromal tumours such as CMN, CCSK and rhabdoid tumour of kidney (RTK). Beckwith has postulated that MST may represent the result of maturation of intralobar nephrogenic rests (INR) with the loss of any active blastemal component. [1],[2] Characteristic histological features of MST include (a) alternating cellularity that imparts a nodular low power appearance (b) onion skin cuffing around entrapped renal tubules (c) heterologous differentiation and vascular alterations (d) juxta glomerular cell hyperplasia and (e) patchy positivity of tumour cells for CD 34, though variable. The last three features are not present in all the cases. [1],[2],[3],[4] Our case did not show heterologous differentiation, angiodysplasia of the vessel wall or juxta glomerular cell hyperplasia. However, the other histological features and patchy positivity for CD34 and negativity for Desmin helped to exclude other neoplasms in the differential diagnosis. MST is differentiated from CMN by its scalloped, subtly infiltrative border, in contrast with the deeply invasive nature of most CMN. Also MST stains for CD34, while CMN is reported to be positive for Desmin. Clinically, patients of MST are older than the known upper limit for those with CMN (CMN is usually a tumour of infancy). MST can be differentiated from CCSK by the regular branching capillary vascular pattern which is characteristic of CCSK but absent in MST. Also, CCSK are uniformly negative for CD34 and S-100. The distinction between MST and metanephric adenofibroma (MAF) was possible due to the absence of discrete epithelial nodules, more characteristic of MAF. [1],[4] The most common presentation as described by Argani et al. [1] is an abdominal mass followed by hematuria, recurrent urinary tract infection (UTI), incontinence, fever, anemia and hypertension. [5] Our patient presented with the complaint of dribbling of urine. As part of the initial work up, ultrasound of the abdomen was performed, revealing a hypo echoic mass arising from the interpole of kidney. MST is a benign tumour that is centered in medulla, but, in one case continous extension through bladder into the prostatic urethra has been reported. The maximum diameter of our tumour was 7.5 cm. Only three cases, out of the thirty one cases described by Argani et al. [1] had a maximum dimension greater than 7.5 cm, the largest in his series measuring 10 cm. None of the five cases reported thereafter [Table 1] were larger than 5.5 cm in diameter. MST mainly affects children; Mc Donald OG et al. [5] and Langer BR et al. [6] have described adult presentations of MST. Most MSTs were previously classified as congenital mesoblastic nephroma until recently, when Beckwith and others re-characterized this neoplasm after reviewing the files of the National Wilm's Tumour Study Pathology Centre. We agree that treatment of these patients should continue to be nephrectomy. An accurate radiological diagnosis is impossible and the role of partial nephrectomy is unclear at this time. At present, all clinical MST should be fully excised in order to establish a definitive diagnosis. Once the diagnosis is confirmed, no further adjuvant therapy is required. Thorough evaluation by an experienced pathologist is essential for the correct diagnosis.{Table 1}


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