Kidney tumor
Childhood tumors
Metanephric stromal tumor


Topic Completed: 4 May 2021

Minor changes: 4 May 2021

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: Metanephric stromal tumor kidney

Ellen D’Hooghe, M.D.
Gordan M. Vujanic, M.D., Ph.D.
Page views in 2020: 1,711
Page views in 2021 to date: 801
Cite this page: D'Hooghe E, Vujanic GM. Metanephric stromal tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumormetastromal.html. Accessed May 7th, 2021.
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
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
Case reports
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

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

Nodularity

Alternating cellularity

Alternating cellularity

"Onion skinning"

"Onion skinning"

Cysts

Cysts


Angiodysplasia

Intratubular growth

Tumor - kidney interface

Angiodysplasia

Intratubular growth

Tumor - kidney interface

CD34

CD34

Positive stains
Negative stains
Molecular / cytogenetics description
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:
    • Characteristic branching capillary vascular pattern
    • Cyclin D1, BCOR positive
  • Stromal type Wilms tumor:
    • Often contains rhabdomyoblasts
    • Often associated with nephrogenic rests
    • More sampling might reveal epithelial or blastemal elements
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?

  1. BCOR+
  2. CD34 positivity of tumor cells
  3. ETV6-NTRK3 gene fusion
  4. Infiltrative tumor - kidney border
Board review style answer #1
B. CD34 positivity of tumor cells

Comment Here

Reference: Metanephric stromal tumor
Board review style question #2
Which of the following is correct regarding metanephric stromal tumor?

  1. It contains a stromal and an epithelial component
  2. It is associated with BRAF V600E mutations
  3. It is treated with surgery and chemotherapy
  4. It never occurs after 3 years of age
Board review style answer #2
B. It is associated with BRAF V600E mutations

Comment Here

Reference: Metanephric stromal tumor
Back to top
Image 01 Image 02