Kidney tumor
Childhood tumors
Metanephric stromal tumor
Editorial Board Members: Maria Tretiakova, M.D., Ph.D., Bonnie Choy, M.D.
Topic Completed: 4 May 2021
Minor changes: 4 May 2021
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PubMed Search: Metanephric stromal tumor kidney
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Pathophysiology | Etiology | Clinical features | Diagnosis | Laboratory | Prognostic factors | Case reports | Treatment | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Molecular / cytogenetics description | Sample pathology report | Differential diagnosis | Additional references | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2Cite this page: D'Hooghe E, Vujanic GM. Metanephric stromal tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumormetastromal.html. Accessed January 19th, 2022.
Definition / general
- Benign pure mesenchymal renal neoplasm
- Belongs to the group of metanephric tumors
- First described by Argani and Beckwith in 2000 (Am J Surg Pathol 2000;24:917)
Essential features
- Rare benign purely mesenchymal renal tumor
- Belongs to metanephric tumors
- 67% of patients between 6 months and 10 years (range 2 days to 56 years)
- Multifocal in ~10% of cases; never bilateral in cases reported to date
- Characteristic alternating cellularity resulting in a nodular appearance
- CD34 positive
- Associated with BRAF V600E mutations
- Treated with radical or partial nephrectomy
- Only 1 recurrence and 1 death (related to vascular abnormalities) reported
Terminology
- Adult mesoblastic nephroma (in the old literature)
ICD coding
- ICD-O: 8935/1 - stromal tumor, NOS
Epidemiology
- Rare tumor, < 50 cases reported in the literature (J Pediatr Urol 2020;16:822)
- Age 2 days to 56 years (median 2 years, mean < 4 years)
- 67% between 6 months and 10 years
- 3 adult cases
- M:F = 1.2:1
Sites
- Kidney; multifocal in ~10% of cases
- Never bilateral
Pathophysiology
- Unknown
- Cytogenetic and molecular studies found no evidence that it is linked to Wilms tumor (Cancer Genet 2011;204:340, Am J Surg Pathol 2016;40:719)
Etiology
- Not known
Clinical features
- Asymptomatic abdominal mass (~53% of patients) (J Pediatr Urol 2020;16:822)
- Always unilateral in reported cases to date
- Abdominal discomfort or pain (~21%)
- Hematuria (17%)
- High blood pressure (~10%)
Diagnosis
- No distinguishing imaging features
- Diagnosed as a renal mass, some with cystic and solid components
- Biopsy unhelpful
Laboratory
- No abnormalities
Prognostic factors
- Benign clinical course
- Only 1 recurrence reported (Urology 2011;78:1411)
- 1 death associated with extrarenal vascular abnormalities (Am J Surg Pathol 2000;24:917)
Case reports
- 2 year old boy presented with a tumor extending into the bladder (J Urol 2003;169:1095)
- 6 year old boy with a cystic and solid renal mass (J Pediatr Surg 2011;46:e7)
- 15 year old boy with a renal tumor (Urology 2001;58:462)
- 53 year old woman with a renal tumor (J Urol 2002;168:1482)
Treatment
- Surgery (radical nephrectomy) is regarded as the only mode of treatment necessary
- Some cases treated with partial nephrectomy
- No chemotherapy necessary
- Reference: J Pediatr Urol 2020;16:822
Gross description
- Centrally located in the renal medulla
- Lobulated, often cystic (~55% of cases)
- Multifocal in ~10% of cases
- 2.5 - 12 cm (median 5 cm)
- Rarely protrudes into renal pelvis (botryoid growth)
- In 5 - 6% of cases, renal artery aneurysms found (Int J Surg Pathol 2011;19:667)
Gross images
Contributed by Ellen D’Hooghe, M.D. and Gordan M. Vujanic, M.D., Ph.D.
Gross appearance
Microscopic (histologic) description
- Well circumscribed and unencapsulated tumor (Am J Surg Pathol 2000;24:917)
- No major infiltration of the renal parenchyma; instead, has a scallop-like border
- Nodular appearance on low power view due to alternating cellularity
- "Onion skin" cuffing around entrapped tubules, which may show:
- Cystic dilatation
- Embryonal hyperplasia
- Intraluminal growth (fibroadenoma-like pattern)
- Vascular changes:
- Angiodysplasia of entrapped arterioles
- Juxtaglomerular cell hyperplasia
- Heterologous elements in ~20% of cases (glial, chondroid but never skeletal muscle)
Microscopic (histologic) images
Contributed by Ellen D’Hooghe, M.D. and Gordan M. Vujanic, M.D., Ph.D.
Nodularity
Alternating cellularity
"Onion skinning"
Cysts
Intratubular growth
Angiodysplasia
Tumor - kidney interface
CD34
Positive stains
- CD34 (97% of cases) (J Pediatr Urol 2020;16:822)
- Vimentin (72%)
Negative stains
Molecular / cytogenetics description
- BRAF V600E mutations reported in ~70% of cases (Am J Surg Pathol 2016;40:719, Hum Pathol 2017;60:32, J Pediatr Urol 2020;16:822)
Sample pathology report
- Kidney, total nephrectomy:
- Metanephric stromal tumor (see comment)
- Comment: Tumor shows a nodular appearance on the low power view due to alternating hypo and hypercellularity of spindle cells. Entrapped renal tubules are surrounded by concentric layers of the same cells ("onion skinning"). There are some blood vessels showing angiodysplasia. The tumor - kidney interface is clearly demarcated with only subtle infiltration. Tumor does not infiltrate the renal sinus or perirenal fat. Tumor cells show strong and diffuse CD34 positivity. Molecular studies show a BRAF V600E mutation. This is a benign tumor, which requires no further treatment.
Differential diagnosis
- Mesoblastic nephroma:
- Up to 3 years of age
- Tumor - kidney border is irregular and infiltrative, with entrapped renal parenchyma
- No nodular appearance
- No vascular changes
- CD34 negative
- No BRAF V600E mutations
- Metanephric adenofibroma:
- Stromal component identical to metanephric stromal tumor
- Epithelial component present (identical to metanephric adenoma)
- Clear cell sarcoma of the kidney:
- Stromal type Wilms tumor:
- Often contains rhabdomyoblasts
- Often associated with nephrogenic rests
- More sampling might reveal epithelial or blastemal elements
Additional references
Board review style question #1
A 3.5 year old boy presented with an abdominal mass. Imaging studies revealed a left sided renal mass. Total left nephrectomy was performed. The tumor was composed of hypocellular and hypercellular areas of spindled cells. Which finding is most characteristic for this entity?
- BCOR+
- CD34 positivity of tumor cells
- ETV6-NTRK3 gene fusion
- Infiltrative tumor - kidney border
Board review style answer #1
Board review style question #2
Which of the following is correct regarding metanephric stromal tumor?
- It contains a stromal and an epithelial component
- It is associated with BRAF V600E mutations
- It is treated with surgery and chemotherapy
- It never occurs after 3 years of age
Board review style answer #2
